Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Cactus Ferruginous Pygmy-Owl as Threatened or Endangered With Critical Habitat, 61856-61894 [2011-25565]
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questions regarding this finding to the
above address.
DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
FOR FURTHER INFORMATION CONTACT:
50 CFR Part 17
[FWS–R2–ES–2011–0086; MO 92210–0–
0008]
Endangered and Threatened Wildlife
and Plants; 12-Month Finding on a
Petition To List the Cactus
Ferruginous Pygmy-Owl as Threatened
or Endangered With Critical Habitat
We, the U.S. Fish and
Wildlife Service (Service), announce a
12-month finding on a petition to list
the cactus ferruginous pygmy-owl
(Glaucidium brasilianum cactorum) as
threatened or endangered and to
designate critical habitat under the
Endangered Species Act of 1973, as
amended (Act). Additionally, the
petition requested that we recognize and
list a western subspecies of the cactus
ferruginous pygmy-owl (Glaucidium
ridgwayi cactorum), or, alternatively,
two potential distinct population
segment (DPS) configurations. After
review of all available scientific and
commercial information, we find that
Glaucidium ridgwayi cactorum is not a
valid taxon, and, therefore, not a listable
entity under the Act. Additionally,
using the currently accepted taxonomic
classification of the pygmy-owl
(Glaucidium brasilianum cactorum), we
find that listing the pygmy-owl is not
warranted at this time throughout all or
a significant portion of its range,
including the petitioned and other
potential DPS configurations. However,
we ask the public to submit to us at any
time any new information concerning
the taxonomy or status of the pygmyowl, as well as any new information on
the threats to the pygmy-owl or its
habitat.
SUMMARY:
The finding announced in this
document was made on October 5, 2011.
ADDRESSES: This finding is available on
the Internet at https://
www.regulations.gov at Docket Number
FWS–R2–ES–2011–0086. Supporting
documentation we used in preparing
this finding is available for public
inspection, by appointment, during
normal business hours at the U.S. Fish
and Wildlife Service, Arizona Ecological
Services Office, 2321 West Royal Palm
Road, Suite 103, Phoenix, AZ 85021–
4951. Please submit any new
information, materials, comments, or
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SUPPLEMENTARY INFORMATION:
Background
Fish and Wildlife Service,
Interior.
ACTION: Notice of 12-month petition
finding.
AGENCY:
DATES:
Steve Spangle, Field Supervisor,
Arizona Ecological Services Office (see
ADDRESSES); telephone 602–242–0210;
or by facsimile 602–242–2513. If you
use a telecommunications device for the
deaf (TDD), please call the Federal
Information Relay Service (FIRS) at
800–877–8339.
Section 4(b)(3)(B) of the Endangered
Species Act (Act) (16 U.S.C. 1531 et
seq.) requires that, for any petition to
revise the Federal Lists of Endangered
and Threatened Wildlife and Plants that
contains substantial scientific and
commercial information that listing a
species may be warranted, we make a
finding within 12 months of the date of
receipt of the petition. In this finding,
we determine whether the petitioned
action is: (1) Not warranted, (2)
warranted, or (3) warranted, but
immediate proposal of a regulation
implementing the petitioned action is
precluded by other pending proposals to
determine whether species are
threatened or endangered, and
expeditious progress is being made to
add or remove qualified species from
the Lists of Endangered and Threatened
Wildlife and Plants. Section 4(b)(3)(C) of
the Act requires that we treat a petition
for which the requested action is found
to be warranted but precluded as though
resubmitted annually on the date of
such finding. Therefore, a new finding
is to be made within 12 months and
subsequently thereafter until we take
action on a proposal to list or withdraw
our original finding. We must publish
these 12-month findings in the Federal
Register.
Previous Federal Actions
On March 20, 2007, we received a
petition dated March 15, 2007, from the
Center for Biological Diversity and
Defenders of Wildlife (petitioners)
requesting that we list the cactus
ferruginous pygmy-owl (Glaucidium
brasilianum cactorum) (pygmy-owl) as a
threatened or endangered species under
the Endangered Species Act (Act) (CBD
and DOW 2007). Additionally, the
petition requested the designation of
critical habitat concurrent with listing.
The petition clearly identified itself as
a petition and included the
identification information, as required
in 50 CFR 424.14(a). We acknowledged
the receipt of the petition in a letter to
the petitioners dated June 25, 2007,
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stating that we were proceeding with a
review of the petition.
The petitioners described three
potentially listable entities of the
pygmy-owl: (1) An Arizona distinct
population segment (DPS) of the pygmyowl; (2) a Sonoran Desert DPS of the
pygmy-owl; and (3) the western
subspecies of the pygmy-owl, which
they identified as Glaucidium ridgwayi
cactorum. As an immediate action, the
petitioners requested that we
promulgate an emergency listing rule for
the pygmy-owl. In our June 25, 2007,
response letter to the petitioners, we
described our evaluation of the need for
emergency listing and stated our
determination that emergency listing
was not warranted for the pygmy-owl.
We also stated that the designation of
critical habitat would be considered if
listing of the pygmy-owl was found to
be warranted.
In the Federal Register of June 2, 2008
(73 FR 31418), we published a 90-day
finding in which we determined that the
petition presented substantial scientific
and commercial information to indicate
that listing the pygmy-owl may be
warranted. A more thorough summary
of previous Federal actions related to
the pygmy-owl can be found in the June
2, 2008 90-day finding (73 FR 31418).
Following the publication of our 90day finding on this petition, we initiated
a status review to determine if listing of
the pygmy-owl was warranted. During
our status review, we solicited and
received information from the general
public and other interested parties on
the status of the pygmy-owl. We
consulted with experts, agencies,
countries, and tribes to gather pertinent
information, and ensure that experts
and affected parties were aware of the
status review and of the opportunity to
provide input. We identified, contacted,
and consulted with a diverse group of
experts and interested persons in an
effort to ensure that we gathered and
evaluated the best available scientific
and commercial information on this
subspecies to inform our 12-month
finding.
On December 12, 2009, we received a
60-day Notice of Intent to Sue from the
petitioners for failure to produce a
timely 12-month finding on their
petition. They subsequently filed suit on
February 17, 2010, in the U.S. District
Court for the District of Arizona. That
complaint was subsequently
consolidated in the U.S. District Court
for the District of Columbia along with
another case filed by the Center for
Biological Diversity and thirteen cases
filed by Wild Earth Guardians, all
related to petition finding deadlines.
The court in the consolidated case
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approved two settlement agreements
between the parties on September 9,
2011. In re Endangered Species Act
Deadline Litigation, Misc. Action No.
10–377 (EGS), MDL Docket No. 2165
(D.D.C. Sept. 9, 2011) (Docs. 55 & 56).
The settlement agreements stipulate that
the Service will submit to the Federal
Register a proposed listing rule or a not
warranted finding for the cactus
ferruginous pygmy-owl no later than the
end of Fiscal Year 2011, which is
September 30, 2011.
This notice constitutes a 12-month
finding for the petition to list the
pygmy-owl as threatened or endangered.
We base our finding on a review of the
best scientific and commercial
information available, including all
substantive information received during
our status review.
In this finding, we first provide
background information on the biology
of the pygmy-owl. Included in this
background is our analysis of the
petitioner’s request that we recognize a
western subspecies of the pygmy-owl
(Glaucidum ridgwayi cactorum), which
represents a proposed change in the
taxonomic classification of the pygmyowl. Then, we consider each of the five
factors listed in section 4(a)(1) of the
Act. For each factor, we first determine
whether any negative impacts appear to
be affecting the pygmy-owl anywhere in
the subspecies’ range, and whether any
of these impacts rise to the level of
threats such that the pygmy-owl is
endangered or threatened throughout its
range, according to the statutory
standard.
After the rangewide assessment, we
evaluate the validity of the petitioned
distinct population segments (DPSs), as
well as other potential DPS
configurations suggested by information
submitted during the status review or by
the ecology, occurrence, and
distribution of the pygmy-owl. This
analysis determines whether any of the
DPS configurations meet the criteria for
discreteness and significance under our
DPS policy (see Distinct Vertebrate
Population Segment section below). We
then evaluate whether there is a
significant portion of the pygmy-owl’s
range that warrants further evaluation,
consistent with the Act’s definitions for
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‘‘endangered species’’ and ‘‘threatened
species,’’ which requires analysis of
whether a ‘‘species’’ is endangered or
threatened within ‘‘a significant portion
of its range’’ (see Significant Portion of
the Range section below). Finally, we
make our finding with regard to the
petitioned action and our evaluation as
described above.
Species Information
Description
The pygmy-owl is in the order
Strigiformes and the family Strigidae. It
is a small bird, approximately 17
centimeters (cm) (6.75 inches (in)) long.
Generally, male pygmy-owls average 58
grams (g) to 66 g (2.0 to 2.3 ounces (oz))
and females average 70 g to 75 g (2.4 to
2.6 oz) (AGFD 2008b, p. 3; Proudfoot
and Johnson 2000, p. 16; Johnsgard
1988, p. 159). The pygmy-owl is reddish
brown overall, with a cream-colored
belly streaked with reddish brown.
Color may vary, with some individuals
being more grayish brown (Proudfoot
and Johnson 2000, pp. 15–16). The
crown is lightly streaked, and a pair of
dark brown or black spots outlined in
white occurs on the nape, suggesting
‘‘eyes,’’ leading to the name ‘‘Cuatro
Ojos’’ (four eyes), as it is sometimes
called in Mexico (Oberholser 1974, p.
451). The species lacks ear tufts, and the
eyes are yellow. The tail is relatively
long for an owl and is reddish brown in
color, with darker brown bars. Pygmyowls have large feet and talons relative
to their body size.
Taxonomy
The petitioners requested that we
recognize a change in the taxonomic
classification of the pygmy-owl (CBD
and DOW 2007, pp. 1–2). In considering
taxonomic data, the Service relies ‘‘on
standard taxonomic distinctions and the
biological expertise of the Department
and the scientific community
concerning the relevant taxonomic
group’’ (50 CFR 424.11(a)) and on ‘‘the
best available scientific and commercial
information’’ (50 CFR 424.11(b)). The
use of specific taxonomic data is at the
discretion of the Service, as long as the
information is reliable and meets the
above standards. With regard to the
pygmy-owl, existing avian checklists
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attempt to present the most current
taxonomic classifications, but
discrepancies among checklists
demonstrate that there is scientific
debate and disagreement over some
accepted taxonomic designations.
Taxonomic changes within these
checklists generally occur as a result of
a proposal to change the existing
taxonomy. Lack of reference to a
proposed taxonomic change within
these checklists cannot be interpreted as
rejection (or acceptance) of a proposed
change. It may simply mean a proposal
has not been submitted or evaluated.
Absolute reliance on one or more of
these avian checklists, absent
consideration of recent studies, would
be arbitrary on the part of the Service.
The Service has the responsibility for
deciding what taxonomic entities are to
be protected under the Act, based on the
best available scientific information. We
address any conflicting information or
conflicting expert opinion by carefully
evaluating the underlying scientific
information and weighing its reliability
and adequacy according to the
considerations of the Act and our
associated policies and procedures.
When we previously listed the
pygmy-owl as endangered in 1997 (62
FR 10730; March 10, 1997), and in all
subsequent regulatory and legal actions,
we followed the currently accepted
taxonomic classification, Glaucidium
brasilianum cactorum. We considered
G. b. cactorum to occur from lowland
central Arizona south through western
Mexico to the Mexican states of Colima
´
and Michoacan, and from southern
Texas south through the Mexican states
of Tamaulipas and Nuevo Leon,
consistent with most of the
contemporary literature (Johnsgard
1988, p. 159; Millsap and Johnson 1988,
p. 137; Oberholser 1974, p. 452;
Friedmann et al. 1950, p. 145), and the
last American Ornithologist Union
(AOU) list that addressed avian
classification to the subspecies level
(AOU 1957) (Figure 1). The AOU
checklist is generally accepted as the
primary authority for avian taxonomic
classification, and the 1957 AOU
checklist description is the currently
accepted taxonomic classification of the
pygmy-owl at the subspecies level.
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The petitioners requested a revised
taxonomic consideration for the pygmyowl based on Proudfoot et al. (2006a, p.
¨
9; 2006b, p. 946) and Konig et al. (1999,
pp. 160, 370–373), classifying the
northern portion of Glaucidium
brasilianum’s range as an entirely
separate species, G. ridgwayi, and
recognizing two subspecies of G.
ridgwayi—G. r. cactorum in western
Mexico and Arizona and G. r. ridgwayi
in eastern Mexico and Texas (Figure 1).
Other recent studies proposing or
supporting the change to G. ridgwayi for
the northern portion of G. brasilianum’s
range have been published in the past
15 years (Heidrich et al. 1995, p. 2, 25;
Navarro-Siguenza and Peterson 2004,
p. 5).
Groups classified within species, such
as subspecies, are important in the
discussion of biodiversity because they
represent the evolutionary potential
within a species. Recognizing this, a
number of existing lists of threatened,
endangered, or special status species
include subspecific groups (Haig et al.
2006, p. 1585). We considered the
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information in these existing lists and
other literature as we evaluated the
petitioned taxonomic classification. The
1957 AOU checklist is the last AOU
checklist that described subspecies.
Subsequent AOU checklists have
limited their descriptions to the species
level only and are, therefore, not helpful
in our evaluation.
In our 90-day finding for this petition
(73 FR 31418), we indicated that the
petition presented reliable and
substantive information that a
taxonomic revision may be warranted.
The suggested taxonomic change is
based on recently published
recommendations (Proudfoot et al.
¨
2006a, p. 9; 2006b, p. 946; Konig et al.
1999, pp. 160, 370–373) to revise
pygmy-owl taxonomy. Various other
publications also provide evidence that
the taxonomic status of the pygmy-owl
has not been resolved (Proudfoot and
¨
Johnson 2000, pp. 4–5; Konig et al.
1999, p. 373; Phillips 1966, p. 93;
Buchanan 1964, p. 107). Information
received during our status review also
indicates that pygmy-owl taxonomy
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needs additional work to resolve current
questions (Johnson and Carothers
2008b, pp. 5–6; Robbins 2008, p. 1;
Voelker 2008, p. 1).
Taxonomic nomenclature for the
pygmy-owl has changed over time.
Originally called Glaucidium
ferrugineum in 1872 by Coues (Coues
1872, p. 370), the pygmy-owl has also
been known as G. ferrugineus (Aiken
1937, p. 29) and G. phalo(a)enoides
(Fisher 1893, p. 199; Gilman 1909, p.
115, Swarth 1914, p. 31; Kimball 1921,
p. 57). Since the 1920’s, the pygmy-owl
has been classified as G. brasilianum
(van Rossem 1937, p. 27; Bent 1938, p.
435; Peters 1940, p. 130; Brandt 1951, p.
653; Sutton 1951, p. 168). We will focus
our discussion at the subspecies level
since the petitioned entity is at the
subspecies level of classification. As
such, we will not evaluate or discuss
whether the appropriate species
classification is G. brasilianum or G.
ridgwayi.
The petitioners asked the Service to
recognize a subspecies, Glaucidium
ridgwayi cactorum, described by
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Mexico, the Lower Rio Grande Valley of
Texas, and northeastern Mexico, for a
general distribution that runs from
central Mexico northward on both sides
of the Sierra Madre mountains into
Arizona and Texas. The range of the
proposed G. r. cactorum does not extend
as far south as G. b. cactorum. The two
G. ridgwayi subspecies proposed by the
petition encompass the northwestern (G.
r. cactorum) and northeastern (G. r.
ridgwayi) extensions of the range of G.
b. cactorum. Specifically, the petition
describes the range of the suggested
subspecies, G. r. cactorum, as extending
from Arizona on the north through the
States of Sonora and Sinaloa in Mexico
(Figure 2).
Our analysis of whether to accept the
petitioners’ proposed Glaucidium
ridgwayi cactorum subspecies as a
listable entity includes an evaluation of
whether there are historical or current
descriptions or studies of the proposed
subspecies that would support the
description of the petitioned subspecies
based on Proudfoot et al. (2006a,
2006b). A number of subspecies of G.
brasilianum have been described or
suggested (Proudfoot and Johnson 2000,
p. 4; Friedmann et al. 1950, pp. 145–
147), including various descriptions of a
cactorum subspecies, the distribution of
some of which generally match the
petitioned subspecies. Therefore, the
delineation of a cactorum subspecies as
petitioned is not a new classification,
but one that has been described
previously in the literature under G.
brasilianum.
With regard to existing literature, van
Rossem (1937, pp. 27–28) described the
earliest cactorum subspecies that
approximates the distribution of the
petitioned subspecies. This was a newly
described subspecies of ferruginous
pygmy-owl and was described from a
‘‘giant cactus grove between Empalme
and Guaymas * * * Sonora, Mexico’’
(van Rossem 1937, p. 27). Van Rossem
restricted this new subspecies to
northwestern Mexico and Arizona
(Figure 3). Van Rossem also included a
more southern and eastern subspecies,
ridgwayi, that was described as
occurring in southern Mexico and
central America, but also Texas (van
Rossem, 1937, pp. 27–28). He
specifically excluded the Texas
population from cactorum, about which
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Proudfoot et al. (2006a, pp. 9–10; 2006b,
p. 2, 9) as the listable entity in the
petition. The primary difference
between the petitioned subspecies and
the currently accepted description of G.
brasilianum cactorum is the latter’s
more extensive distribution to the south
and east (Figure 1). The range of the G.
b. cactorum subspecies we originally
listed in 1997 is Arizona, northwestern
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he wrote ‘‘they approximate very closely
the measurements and tail characters of
cactorum * * * in color they are best
referred to ridgwayi’’ (van Rossem 1937,
pp. 27–28; italics added). The 1944
AOU checklist accepted this
classification and described its
distribution as southern Arizona to
Nayarit, in western Mexico (AOU 1944,
p. 50) (Fig. 3). However, in a later
publication van Rossem (1945, p. 111)
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indicated that cactorum extended only
to the Sonora and Sinaloa border in
Mexico (Figure 3), perhaps excluding
Nayarit, because his 1937 publication
indicates that the specimen from
Nayarit was not typical (van Rossem
1937, p. 28). Karalus and Eckert (1971,
p. 223) give a southern distribution for
cactorum of western and northwestern
Sonora (Figure 3). Proudfoot et al.
(2006a, p. 9; 2006b, p. 7) indicate the
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state of Sinaloa is the southern extent of
¨
the range, while Konig et al. (1999, p.
373) extend the distribution of cactorum
into Nayarit and Jalisco in western
Mexico (Figure 3). Freethy (1992, p.
121) simply states that western Mexico
is the southern limit of cactorum.
Clements (2007, p. 171) recognizes the
cactorum subspecies, but gives no
distribution.
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The chronology described in the
previous paragraph, which excludes the
currently accepted distribution of
Glaucidium brasilianum cactorum,
focuses on descriptions in the literature
which generally approximate the
petitioned description of G. ridgwayi
cactorum, and there is consensus that
cactorum extended northward into
Arizona. However, it is evident there is
inconsistency regarding the southern
extent of the subspecies. With the
exception of van Rossem (1937, pp. 27–
28), who uses morphological
characteristics to describe the
subspecies, most of the above
descriptions of the cactorum subspecies
do not indicate why they have ascribed
the subspecies to the ranges indicated in
¨
these publications. Konig et al. (1999, p.
373) simply uses the morphological
characters of van Rossem (1937, pp. 27–
¨
28). Konig et al. (1999, entire) and
Proudfoot et al. (2006a; 2006b, entire)
do classify cactorum using genetic data,
but draw different conclusions with
regard to the southern boundary. The
incremental southward extension of the
various cactorum ranges may provide
some support for the idea of a clinal
pattern of differentiation in which
genetic and morphological differences
occur in an incremental manner, as
opposed to more abrupt changes that are
more likely to represent a boundary
between two distinct subspecies
groupings. The data presented in the
petition (Proudfoot et al. 2006a; 2006b,
entire) are not sufficient to clarify the
groupings in the literature, nor does it
allow us to determine if the subspecies
ranges are distinct because there is a
lack of adequate sampling in southern
and eastern Mexico. The uncertainty of
the southern boundary would suggest
that additional sampling is needed to
refine this portion of the range of
cactorum. In the presence of unresolved
inconsistencies, the Service relies upon
the ‘‘standard taxonomic distinctions
(50 CFR 424.11(a)); in this case, the
currently accepted taxonomic
classification (AOU 1957).
In addition to reviewing historical
and current descriptions of the
subspecies, we requested review and
input on the issue of taxonomic
classification of the petitioned entity
from 10 individuals with biological
expertise and background in this issue.
Of the 10 we consulted, 5 provided
comments on specific questions we
asked regarding the issues of taxonomic
classification, genetic differentiation,
and genetic diversity based on recent
and historical studies and publications
related to pygmy-owl taxonomic
classification. Information submitted by
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all five experts indicated that, while
there are certain aspects of the
information presented in the petition
that support acceptance of the
petitioned entity, there is insufficient
information regarding how to define a
distinct subspecies. Additional work is
needed to clarify the distribution of the
subspecies, especially in regards to the
southern boundary (Voelker 2008, p. 1;
Cicero 2008, p. 2; Robbins 2008, p. 1;
Oyler-McCance 2008, pp. 1–2;
Dumbacher 2008, pp. 2–8). A summary
of their comments is presented below.
Dumbacher (2008, p. 7) provided a
summary of considerations in response
to our request for input on this issue:
‘‘In summary, Proudfoot et al. 2006a
and 2006b do not provide a critical test
for the subspecies Glaucidium ridgwayi
ridgwayi or G.r. cactorum or their
geographical ranges. The data are
consistent with current subspecies
names in that they show: (1) Isolation by
distance across the range, albeit with
larger genetic breaks in the region that
corresponds with the subspecies names
[as described by van Rossem 1937]; (2)
and significant variation among major
geographical areas that broadly
correspond to present subspecies names
[van Rossem 1937]. However, it is not
clear: (1) Where exactly the subspecies
boundaries occur; (2) whether the
boundary will be geographically distinct
or correspond to characters used in the
original subspecies designation, such
that the two groups would qualify for
subspecies under the 75 percent rule [75
percent of individuals in a new
subspecies (or region) are diagnosably
different from the other possible
subspecies]; or (3) whether a broad
hybrid zone or cline would be
discovered that might call the two
subspecies into question. Further data
are needed to critically test the validity
of the subspecies and to identify the
most appropriate geographic boundary
between them. Proudfoot et al. (2006b)
make a plea for more data in critical
areas, such as between Sonora and
Sinaloa, and I would argue further south
as well.’’
Cicero (2008, p. 2) adds, ‘‘On the basis
of these data, I would argue that Arizona
and Texas populations should be
managed as separate units. However,
further study of the variation in
morphology and plumage (the
characters originally used to describe
cactorum) is needed before we can
reliably apply names to these
populations. Thus, in my opinion, the
molecular data provided by Proudfoot et
al. (2006a and 2006b) do not clarify
subspecific limits and ranges in North
American populations of G.
brasilianum’’. Similarly, Oyler-McCance
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(2008, p. 2) indicates that, ‘‘within the
United States, it is clear that the Arizona
group is much different from the Texas
group and should not be considered as
one group. What is less clear, however,
is where exactly to draw the boundary
between the two subspecies * * *. It
would be informative to look at other
characteristics (morphology, behavior,
geographic distribution) and see how
well they fit with the patterns provided
by the genetic data. Only then, using all
those characteristics, would it be
prudent to make a decision.’’
Robbins (2008, p. 1) indicated that
work on a molecular-based phylogeny of
New World pygmy-owls is about to be
completed that will inform this issue.
He suggested that acceptance of the
petitioned entity be delayed until this
work has been published. However, the
study to which Robbins refers will focus
on species-level analyses, and it may
not provide additional information
regarding the distribution of subspecies
and, as of the date of this finding, has
not yet been published.
Recently, the Committee on
Classification and Nomenclature on
North and Middle American birds (the
Checklist Committee) of the AOU
considered a proposal to separate
Glaucidium brasilianum ridgwayi as a
distinct species, but rejected that
proposal, citing the need to wait for
additional work (AOU 2009).
In fairness to Proudfoot and his
collaborators, their two 2006 studies are
more general in nature and did not have
the objective of defining pygmy-owl
classification to the subspecies level. In
addition, Proudfoot and his fellow
authors, similar to the authors of many
other publications related to pygmy-owl
taxonomy, pointed out the need for
additional work to clarify the taxonomic
classification of pygmy-owls. Therefore,
when we consider the recent
information provided by Proudfoot et al.
¨
(2006a; 2006b, entire) and Konig et al.
(1999, entire), in combination with the
historical descriptions of distributions
for the subspecies cactorum, there is
evidence of a general nature that the
petitioned subspecies may have merit.
However, after reviewing the best
available information, we find that
uncertainty and inconsistency exists
with regard to the delineation of the
range of these subspecies.
The peer reviewers who provided
information to the Service regarding this
issue represent respected experts with
considerable knowledge of the current
science regarding avian taxonomy and
classification. They point out that a
combination of factors, including
morphological, vocal, and genetic, need
to be considered in greater depth, with
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additional sampling, to determine if the
petitioned taxonomic classification
should be accepted, and we are in
agreement with these comments. Given
the uncertainty and lack of clarification
found in the best available scientific and
commercial information, we rely on the
‘‘biological expertise of the Department
and the scientific community
concerning the relevant taxonomic
group’’ (50 CFR 424.11(a)).
In summary, we find that there is
considerable uncertainty as to whether
the genetic differentiation found at the
far ends of the pygmy-owl’s distribution
represented by Arizona and Texas are
adequate to define the eastern and
western distributions as separate
subspecies. These differences may
simply represent isolation by distance
with a clinal gradation of genetic
differentiation between the two
extremes of the range, which would be
inconsistent with the existence of two
different subspecies. Therefore, the best
available scientific and commercial
information does not suggest that
genetic differentiation reported by
Proudfoot et al. (2006a; 2006b, entire)
¨
and Konig et al. (1999, entire) supports
their proposed Glaucidium ridgwayi
cactorum subspecies classification at
this time. Future work and studies may
clarify and resolve these issues, but, in
the meantime, we will continue to use
the currently accepted distribution of G.
brasilianum cactorum as described in
the 1957 AOU checklist and various
other publications (Johnsgard 1988, p.
159; Millsap and Johnson 1988, p. 137;
Oberholser 1974, p. 452; Friedmann et
al. 1950, p. 145). The Service accepted
this information under the previous
listing of the pygmy-owl (62 FR 10730).
We, therefore, reject the petitioned
listing of a western subspecies of
pygmy-owl, G. r. cactorum, as an
insufficiently supported taxonomic
subspecies at this time.
The following discussion will
examine the potentially listable entities
of Glaucidium brasilianum cactorum,
the currently recognized subspecies of
pygmy-owl.
Distribution and Status
The currently accepted distribution of
the pygmy-owl is described as south
central Arizona and southern Texas in
the United States, south through the
Mexican States of Sonora, Sinaloa,
´
Nayarit, Jalisco, Colima, and Michoacan
on the west and Nuevo Leon and
Tamaulipas on the east (Figure 1).
Available information on the specific
distribution of the pygmy-owl within
this general area is not comprehensive,
especially in the southern portions of
Mexico. As described below, we have
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relatively detailed information on
pygmy-owl distribution in the United
States and Sonora, Mexico. The
following is a description of the
available information we have related to
the distribution of the pygmy-owl.
The cactus ferruginous pygmy-owl is
the northernmost subspecies of the
ferruginous pygmy-owl. This subspecies
was originally described as being
common in the lower Rio Grande River
in southern Texas (Oberholser 1974, p.
452) and along the Salt and Gila Rivers
in central Arizona (Fisher 1893, p. 199;
Breninger 1898, p. 128; Gilman 1909, p.
148). In Arizona and Texas, apparent
range and population declines have
occurred, reducing the current
distribution of the pygmy-owl in these
areas (Oberholser 1974, p. 452; Monson
and Phillips 1981, p. 72; Proudfoot and
Johnson 2000, p. 3). Historical records
for the pygmy-owl in Arizona span at
least five counties in southern and
south-central Arizona, including
Maricopa, Pima, Pinal, Santa Cruz and
Yuma Counties (Johnson et al. 2003, p.
394). Most of the historical (pre-1900)
and recent (post-1990) records are from
Pima County. Between 1872 and 1971,
a total of 56 published records or
specimens were recorded for Arizona.
Of those, almost half (27) were from
Pima County (Johnson et al. 2003, pp.
392–395). Although the pygmy-owl was
historically recorded primarily from
lowland riparian habitats, all recent
records are from upland and
xeroriparian (vegetation community in
drainages associated with seasonal or
intermittent water) Sonoran desertscrub
(Abbate et al. 2000, pp. 15–16, Service
2009b, p. 1: 2011, p. 1).
Some information provided by the
public suggested that the pygmy-owl is
an obligate wet riparian species in
south-central Arizona and a preferential
wet riparian species in southern
Arizona, tying its distribution to these
types of areas. In addition, the
information states that recent records in
upland habitats have occurred primarily
in areas associated with ‘‘cultivated
riparian’’ habitats resulting from the
human influences of irrigation and
ornamental plantings, such as in
suburban areas of Tucson (Johnson and
Carothers 2008b, pp. 13–14). We agree
that riparian ecosystems provide
important pygmy-owl habitat within its
range. However, we disagree with the
suggestion that pygmy-owls are riparian
obligates, and thus limited in
occurrence to these areas. For example,
there are numerous recent locations in
which pygmy-owls were detected in
Sonoran desert uplands and semi-desert
grasslands of southern Pinal County,
Avra Valley, Altar Valley, Cabeza Prieta
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National Wildlife Refuge, Organ Pipe
Cactus National Monument, and
northern Sonora that are not in
proximity to ‘‘cultivated riparian’’ or
naturally occurring hydro- or
mesoriparian (wet riparian) habitats.
Two members of the public provided
extensive information in support of the
idea that pygmy-owls have never been
common in Arizona; therefore, the
current low numbers and reduced
distribution are not sufficient reason to
determine that the pygmy-owl is
endangered in Arizona (James 2008, pp.
8–10; Parker 2008, pp. 2–10). This
conclusion is based on the historical
records from early naturalists and
ornithologists regarding their
observations or collections of pygmyowls or their nests or eggs, or the lack
thereof. Specifically, this information
points out that a number of early
naturalists or ornithologists that made
trips of various lengths and in various
locations in Arizona where pygmy-owls
would have been expected to occur did
not make mention of observing pygmyowls in their trip reports (James 2008,
pp. 46–48; Parker 2008, pp. 6–8). We
appreciate the effort and research
represented by this information. It
provides an excellent summary of
historical ornithological efforts in
Arizona. In assessing the information
provided, we must determine if it is
comparable to the information currently
available on pygmy-owl numbers and
distribution in Arizona. Current
information comes from extensive
surveys focused on locating only
pygmy-owls using tape-playback or call
imitation to locate the owls. We can find
no evidence from the information
provided that this same effort or
methodology was used to locate pygmyowls in the historical record; thus
comparison with current surveys is not
appropriate.
We do not discount the ability of early
naturalists and ornithologists to find
and identify pygmy-owls. However,
finding pygmy-owls was not the
objective of the trips reported in the
literature, and unfortunately, most of
these early reports do not contain
enough information for us to determine
that the effort was adequate to find
pygmy-owls if they were present or that
the absence of documentation of pygmyowls truly means that no pygmy-owls
were encountered. Additional
information received from the public
points out the problems in interpreting
these early reports, ‘‘While certainly
instructive as to the critical value of
surface water diversions, irrigation, and
agriculture to Cactus ferruginous pygmy
owls, lack of necessary specific
information prevents Breninger’s 1898
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account from serving as a source of
support for the petitioner’s claim that
this owl was historically common across
the lowlands of central and southern
Arizona. This is because Breninger
neither shows how much time he spent
in the field nor the locations he actually
visited along either the Salt and Gila
Rivers that caused him to conclude that
Cactus ferruginous pygmy owls were
then ‘‘of common occurrence’’ ‘‘among
the growth of cottonwood’’ that fringed
both on a highly localized basis’’ (Parker
2008, pp. 3–4).
While early records provide
information that shows the range of the
pygmy-owl has contracted in Arizona,
this conclusion relies on information at
a large scale and is not dependent on
specific population numbers, only
presence or absence. The logical
assumption may follow that pygmy-owl
numbers are likely reduced as well.
However, these early records do not
have enough specific information for us
to quantify historical pygmy-owl
population numbers in a way that
allows comparison to our current
information. Glinski (1998, p. 3)
provides a summary of this issue in The
Raptors of Arizona, ‘‘From the
perspective of the variety and numbers
of raptors, what did Arizona’s landscape
harbor two centuries ago? Is the answer
to this question in the early literature?
Unfortunately, no. Detailed records that
accurately depict the status of Arizona
raptors before 1970 are entirely lacking.
The records of early explorers are full of
errors, and later interpretations of them
have added to the problem (G.P. Davis
1982).’’
We received information from various
agencies and municipalities that
contained survey results from Arizona
indicating that the pygmy-owl is likely
absent from some areas in Maricopa and
Pima Counties. Survey data submitted
by the USDA Forest Service covering
over 4,050 hectares (ha) (10,000 acres
(ac)) in a 6-year period on the Tonto
National Forest in Maricopa County
detected no pygmy-owls (USFS 2008, p.
1). Burger (2008, p.1) indicated that the
Arizona Game and Fish Department
(AGFD) had conducted 3 years of
surveys in Maricopa County without
any pygmy-owl detections. Annual
pygmy-owl surveys have been
conducted by the Air Force on the Barry
M. Goldwater Range of southwestern
Arizona from 1993 to the present with
no verified pygmy-owl detections (Uken
2008, p. 1). The Pima County
Department of Transportation conducts
pygmy-owl surveys for their capital
improvement projects. These pygmyowl surveys are associated with specific
projects, and do not represent
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systematic surveys throughout Pima
County. To date, they have conducted
383 surveys at 152 locations in Pima
County with no detections (Pima
County 2008, p.1). Some of the above
surveys, and other negative surveys
conducted throughout Arizona since
1997, occurred in areas where the
pygmy-owl was historically located.
This provides strong evidence that the
current range of the pygmy-owl in
Arizona has contracted.
Currently in Arizona, the pygmy-owl
is found only in portions of Pima and
Pinal Counties. The Arizona Breeding
Bird Atlas reports confirmed
occurrences of the pygmy-owl in only
three blocks distributed in Pima and
Pinal Counties (Arizona Breeding Bird
Atlas (ABBA) 2005, p. 219). Twelve
other blocks recorded probable (3) or
possible (9) occurrences, but none
occurred outside of Pima and Pinal
Counties (ABBA 2005, p. 219). Recent
surveys indicate that probably fewer
than 50 adult pygmy-owls exist in the
state, with 10 or fewer nest sites on an
annual basis (Abbate et al. 2000, pp. 15–
16, AGFD unpublished data). However,
since the pygmy-owl was delisted in
2006 (71 FR 194521; April 14, 2006),
surveys, monitoring, and other research
on pygmy-owls has declined. Limited
survey and monitoring in Arizona from
2009 to 2011 documented that pygmyowls still occupy historical locations in
the Altar Valley, Avra Valley, and Organ
Pipe Cactus National Monument, all
within Pima County (Service 2009b, p.
1; Tibbitts 2011, p. 1; Service 2011, p.
1). Comprehensive surveys have not
been conducted on the Tohono
O’odham Nation (Nation), which is
located in the central portion of both the
historical and current distribution of
pygmy-owls in Arizona. However, a
number of surveys have been completed
for various utility projects on the
Nation, and the pygmy-owl is known to
occur there. Distribution of the data
from these surveys has been restricted
by the Nation and is not available for
analysis. There are large areas of
suitable habitat on the Nation, but the
information we have indicates that
pygmy-owls are patchily distributed,
just as in other areas of the State, and
occur at similar densities.
In summary, because the early records
found in the literature provide no basis
for consistent interpretation, the
statements that the pygmy-owl was ‘‘not
uncommon,’’ ‘‘of common occurrence,’’
and ‘‘fairly numerous’’ in lowland
central and southern Arizona may be as
appropriate as the commenter’s
interpretation that the pygmy-owl was
never common in Arizona. The bottom
line is that these early records provided
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no quantifiable information on which to
base trends in pygmy-owl populations.
Consequently, we must base our
evaluation of the current pygmy-owl
status on the best available scientific
and commercial data, which is the
information that does, at least, provide
some ability to quantify pygmy-owl
population numbers. Regardless of the
lack of quantified historical data, the
early records found in the literature give
us some idea of the historical
distribution of the pygmy-owl in
Arizona that, when compared to the
current distribution, has unquestionably
been reduced.
In Texas, the pygmy-owl was formerly
common in the Rio Grande delta.
Griscom and Crosby (1926, p. 18)
reported that the pygmy-owl was
considered a ‘‘common breeding
species’’ in the Brownville region of
southern Texas. Even as late as 1950,
Friedman et al. (1950, p. 145)
considered the pygmy-owl to be ‘‘a very
common breeding bird.’’ However,
Oberholser (1974, pp. 451–452)
indicates that agricultural expansion
and subsequent loss of native woodland
and thornscrub habitat, beginning in the
1920s, preceded the rapid demise of the
pygmy-owl populations in the Rio
Grande delta. By the 1970s, the pygmyowl was encountered only rarely in
Texas.
Nonetheless, Wauer et al. (1993, pp.
1074–1076) indicate that private
ranches in Kenedy and Brooks Counties
in Texas support a ‘‘large and
apparently thriving population of
ferruginous pygmy-owls.’’ Currently, the
pygmy-owl is most consistently found
only in the southernmost counties in
Texas, mainly in Starr and Kenedy
Counties (Tewes 1992, p. 21; Oberholser
1974, p. 451). More recent work
documents occupancy in Brooks and
Kenedy Counties on the King Ranch and
adjacent ranches in Texas (Proudfoot
1996, p. 6; Mays 1996, p. 29).
Population estimates in Texas include
estimates of greater than 100 owls in
Kleberg County (Tewes 1992, p. 24), 654
pairs in Kenedy, Brooks, and Willacy
Counties (Wauer et al. 1993, p. 1074),
and 745 to 1,823 pygmy-owls on
ranches in Kenedy and Brooks Counties
(Mays 1996, p. 32).
Recent concern about the populations
in Texas has been raised because of an
apparent decline in the number of
pygmy-owl nestlings banded as part of
an ongoing nest box study in Texas
(Proudfoot 2010, p. 1). The numbers of
nestlings banded at more than 200 nest
boxes in 2003 and 2004 were 84 and 96
respectively. The numbers suggest a
steady decline from 2004 to 2010, with
25 and 24 nestlings banded in 2009 and
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2010, respectively (Proudfoot 2010, p.
1). This represents an approximate 70
percent decline in the number of
nestlings banded over an 8-year period.
Proudfoot (2011b, p. 1) indicates this
decline is likely the result of the loss of
suitable habitat around nest boxes due
to recent hurricanes and fires. Without
a more comprehensive survey effort in
southern Texas, we cannot definitively
state that the overall population of
pygmy-owls in south Texas matches the
decline of nestlings documented during
this nest box study. However, it does
raise our level of concern for this
population. More work is needed in
Texas to determine the overall
population status and the extent of
habitat loss and fragmentation. It may
simply be that the pygmy-owls in these
areas have moved to adjacent suitable
habitat as former habitat and the
associated nest boxes have been
destroyed.
The pygmy-owl occurs in portions of
eight States in Mexico. The pygmy-owl
was thought to be uncommon
throughout much of Sonora (Russell and
Monson 1998, p. 141; Hunter 1988, pp.
1–6). However, recent surveys and
capture efforts have shown that the
pygmy-owl commonly occurs in both
northern and southern Sonora, but is
uncommon or absent in central Sonora
(Flesch 2003, p. 39; AGFD 2008a, p.6;
Service 2009a, p. 1). The highest
densities of pygmy-owls occurred in the
Sinaloan deciduous forest of southern
Sonora (Flesch 2003, p. 42). Flesch
(2003, p. 39) documented 438 males, 74
females, and 12 pygmy-owls of
unknown sex along 1,113 kilometers
(km) (1,780 miles (mi)) of transects in
Sonora, and an additional 112 pygmyowls incidentally detected.
During capture efforts in 2008, AGFD
(2008a, p. 6) documented multiple
pygmy-owls commonly responding at
capture sites in the thornscrub and
tropical deciduous forests of southern
Sonora. In areas of central Sonora
sampled by AGFD, some sites had no
pygmy-owl responses, but responses
increased as sampling moved into
northern Sonora. These results are
similar to patterns of occupancy
documented by Flesch (2003, p. 40).
However, it is clear that the number and
density of pygmy-owls is higher in the
thornscrub and deciduous forest
community types than in the Sonoran
desert community type. This occurrence
and distribution agrees with
conclusions found in the literature
(Hunter 1988, p. 7; Russell and Monson
1988, p. 141; Shaldach 1963, p. 40). A
total of 119 pygmy-owls were captured
by AGFD over 15 days of trapping in
northern Sinaloa and Sonora (AGFD
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2008a, p. 6). The most recent monitoring
of pygmy-owls in northern Sonora
showed that, in 2010, sites sampled had
the highest occupancy rates in the past
10 years at nearly 64 percent (Flesch
2011, p. 1). However, early results from
the 2011 monitoring show occupancy of
these same sites at around 50 percent,
not far from the 10-year low of 45.7
percent (Flesch 2011, p. 1).
In summary, recent surveys and
research in northwestern Mexico
indicate that numbers and density of
pygmy-owls are higher in thornscrub
and tropical deciduous forest
communities of southern Sonora and
Sinaloa than in the Sonoran desertscrub
and semi-desert grassland vegetation
communities of the Sonoran Desert
Ecoregion (Flesch 2003, pp. 39–42;
AGFD 2008a, p. 6).
The best available information we
have from the literature for the southern
portion (areas south of Sonora and
northern Sinaloa) of the pygmy-owl
range indicates that pygmy-owls are one
of the most common birds collected in
these areas (Cartron et al. 2000, p. 5;
Enriquez-Rocha et al. 1993, p. 154;
Binford 1989, p. 132; Hunter 1988, p. 7;
Johnsgard 1988, p. 161; Oberholser
1974, p. 451; Schaldach 1963, p. 40). It
is important to note, however, that most
of these references apply to the
ferruginous pygmy-owl as a species and
not to the cactorum subspecies
specifically. However, the more recent
survey, monitoring, and capture work
discussed above all occurred within the
range of the cactorum subspecies.
Tewes (1993, pp. 15–16) provides the
most current information on pygmyowls in northeastern Mexico. During
surveys in 1991, he estimated 96
pygmy-owls in association with 142
plots at 12 locations (Tewes 1993, pp.
15–16). He concludes that no published
empirical evidence suggests any change
in the distribution of this species in
Texas or northeastern Mexico, although
the likelihood of finding pygmy-owls is
low in some historically occupied areas
(Tewes 1993, p. 22).
In addition, pygmy-owls are not
evenly distributed across their current
range; rather they tend to be patchily
distributed across the landscape.
Pygmy-owl populations, particularly in
the northern portion of its range, likely
function as metapopulations (a group of
spatially separated populations that act
at some levels as a single large
population). Genetic and population
support for individual groups of pygmyowls likely occurs as a result of
dispersal. Therefore, habitat
connectivity among these population
groups is important to maintain genetic
diversity, as well as demographic
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support. Interaction among these
population groups likely varies with
distance, but pygmy-owls have been
documented to disperse up to 260 km
(161 mi.) (AGFD 2008a, p. 5). Individual
pygmy-owl groups throughout the range
are important to the survival of the
subspecies as a whole in providing
metapopulation support.
In conclusion, pygmy-owl
distribution in the United States has
contracted, with pygmy-owls no longer
found in Maricopa, Cochise, Yuma, and
Santa Cruz Counties in Arizona, nor in
the Lower Rio Grande Valley in Texas.
Despite this range contraction in the
United States, pygmy-owls remain in
Arizona and Texas. Survey results for
Arizona indicate that approximately 50
adult pygmy-owls remain. In addition,
there are a few large expanses of
Arizona with suitable pygmy-owl
habitat that have not been completely
surveyed or for which pygmy-owl
information is not available for
evaluation. Pygmy-owl populations in
Texas are estimated to range up to 1,800
birds, although there have been some
declines in pygmy-owl nestlings
associated with a nest box study in
Texas. Pygmy-owls are still found in
Sonora and northern Sinaloa, with
higher densities reported in thornscrub
and dry tropical forested areas
compared to the arid desert areas. Based
on Tewes study (1993, entire), pygmyowls still occupy suitable habitat in
northeastern Mexico and the pygmyowl’s distribution remains unchanged in
Texas and northeastern Mexico. In
addition, it appears that pygmy-owls
still occur in the same areas of Mexico
reported in the literature, suggesting
that the current distribution is similar to
the historical distribution. The available
information, although dated, suggests
that pygmy-owls remain common in the
southern portion of their range.
Habitat
Pygmy-owls are found in a variety of
vegetation communities, including
Sonoran desertscrub and semidesert
grasslands in Arizona and northern
Sonora, thornscrub and dry deciduous
forests in southern Sonora south to
´
Michoacan, and Tamaulipan brushland
in Texas and northeastern Mexico.
However, available information
regarding specific pygmy-owl habitat
elements within these vegetation
communities is limited to Arizona,
Texas, and northern Sonora.
In Arizona, pygmy-owls rarely occur
below 300 meters (m) (1,000 feet (ft)) or
above 1,200 m (4,000 ft) (Proudfoot and
Johnson 2000, p. 5), except perhaps
during dispersal (AGFD 2008b, p. 3).
Historically, in Arizona, the pygmy-owl
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nested in Fremont cottonwood-mesquite
forests and mesquite bosques
(woodlands) associated with major
drainages and their tributaries and the
subspecies is considered by some to be
a preferential riparian nesting species.
The pygmy-owl in Arizona also
occupies upland Sonoran desertscrub,
often associated with xeroriparian areas.
Species associated with these areas are
Prosopis spp. (mesquite), Parkinsonia
spp. (palo verde), Acacia spp. (acacia),
Olneya tesota (ironwood), and
Carnegiea gigantea (saguaro cactus)
(Proudfoot and Johnson 2000, p. 5).
In Texas, the pygmy-owl was
historically found in Prosopis spp.,
Ebenopsis ebano (ebony), and
Arundinaria gigantea (cane) along the
Rio Grande River, and a more general
distribution in riparian trees, brush,
palm, and mesquite thickets (Oberholser
1974, p. 451). It is now found primarily
in undisturbed live oak-mesquite forests
and mesquite brush, ebony, and riparian
areas of the historical Wild Horse Desert
north of Brownsville, Texas (Proudfoot
and Johnson 2000, p. 5).
In Mexico, the pygmy-owl occurs
from sea level to 1,200 m (4,000 ft)
(Friedmann et al. 1950, p. 145). In
Sonora, it was originally common in the
lower Sonoran and Tropical Zones,
primarily in giant cactus associations
(van Rossem 1945, p. 111). The
subspecies is resident throughout most
of the desertscrub, tropical thornscrub,
and dry subtropical forests of Sonora,
being most common in the latter
association (Russell and Monson 1998,
p. 141). The pygmy-owl is absent from
tropical deciduous forests and higher
vegetation zones in west Mexico, where
it is replaced by the least pygmy-owl
(Glaucidium minutissimum) and the
northern pygmy-owl (G. gnoma)
(Schaldach 1963, p. 40; Buchanan 1964,
pp. 104–105), as well as the Colima
pygmy-owl (G. palmarum) (Howell and
Robbins 1995, pp. 19–20). Dry,
subtropical forests provide important
pygmy-owl habitat elements, as
evidenced by pygmy-owls being more
common in this vegetation community
type than in other community types in
Mexico. The dry, subtropical forests
comprise the majority of the pygmyowl’s southern range in Mexico. The
presence of large trees and columnar
cacti for nesting, and diversity of cover
and prey types, contribute to the value
of dry subtropical forests as pygmy-owl
habitat.
The pygmy-owl is a creature of edges
found in semi-open areas of thorny
scrub and woodlands in association
with giant cacti, scattered patches of
woodlands in open landscapes, mostly
dry woods, and evergreen secondary
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¨
growth (Konig et al. 1999, p. 373). It is
often found at the edges of riparian and
xeroriparian drainages and even habitat
edges created by villages, towns, and
cities (Proudfoot and Johnson 2000, p. 5;
Abbate et al. 1999, pp. 14–23). The
pygmy-owl is a secondary cavity nester,
and nests occur within woodpecker
holes and natural cavities in giant cacti,
but also in trees and even in a sand bank
(Flesch 2003, pp. 130–132; Proudfoot
and Johnson 2000, p. 11; Russell and
Monson 1998, p. 141; Johnsgard 1988, p.
162). Tewes (1992, p. 22) contends that
status and occurrence of the pygmy-owl
is related to the availability of nest
cavities.
While native and nonnative plant
species composition differs among the
various locations within the range of the
pygmy-owl, there are certain unifying
characteristics such as the presence of
vegetation in fairly dense thickets or
woodlands; the presence of trees,
saguaros, Stenocereus thurberi (organ
pipe cactus), or other columnar cacti
large enough to support cavities for
nesting; and elevations typically below
1,200 m (4,000 ft) (Swarth 1914, p. 31;
Karalus and Eckert 1974, p. 218;
Monson and Phillips 1981, pp. 71–72;
Johnsgard 1988, Enriquez-Rocha et al.
1993, p. 158; Proudfoot 1996, p. 75;
Proudfoot and Johnson 2000, p. 5).
Large trees provide canopy cover and
cavities used for nesting, and the
density of mid- and lower-story
vegetation provides foraging habitat and
protection from predators and
contributes to the occurrence of prey
items (Wilcox et al. 2000, pp. 6–9).
Life History
Usually, pygmy-owls first nest as
yearlings (Proudfoot and Johnson 2000,
p. 13; Abbate et al. 1999, pp. 17–19),
and both sexes breed annually
thereafter. Territories normally contain
several potential nest and roost cavities
from which responding females select a
nest. Hence, cavities per unit area may
be a fundamental criterion for habitat
selection. Historically, pygmy-owls in
Arizona used cavities in cottonwood,
mesquite, and ash trees, and saguaro
cacti for nest sites (Millsap and Johnson
1988, pp. 137–138). Recent information
from Arizona indicates nests were
located in cavities in saguaro cacti for
all but two of the known nests
documented from 1996 to 2002 (Abbate
et al. 1996, p. 15; 1999, p. 41; 2000, p.
13; AGFD 2003, p. 1). Pygmy-owl nests
in Texas were primarily in mesquite and
live oak trees (Proudfoot 1996, pp. 36–
38), and nests in Sonora, Mexico, were
nearly always in columnar cacti (Flesch
and Steidl 2002, p. 6). Pygmy-owls will
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also use nest boxes for nesting
(Proudfoot 1996, p. 67).
Pygmy-owls begin courtship and
advertisement calls early in the year
from January into February. Nest
selection then occurs, with eggs
typically being laid from late March into
June. Average clutch size as reported by
Johnsgard (1988, p. 162) for the United
States and Mexico was 3.3 (range 2 to
5, n = 43). In Texas, Proudfoot and
Johnson (2000, p. 11) report an average
clutch size of 4.9 (range 3 to 7, n = 58).
First eggs hatch generally around midMay, and fledging occurs from late-May
through June. The first dispersal of
fledglings in Arizona and Texas was
documented as July 24th and August
14th, respectively (Proudfoot and
Johnson 2000, p. 10). Pygmy-owl
juveniles typically disperse at 8 weeks
post-fledging. Males typically disperse
shorter distances than females.
Dispersal distance ranges from 2.5 to
20.91 km (1.55 to 13.00 mi) in Arizona
(Abbate et al. 2000, p. 21) and 16 to 31
km (9.6 to 18.6 mi) in Texas (Proudfoot
and Johnson 2000, p. 13). One juvenile
female pygmy-owl in Arizona recently
dispersed a total of 260 km (161 mi)
between August 2003 and April 2004
(AGFD 2008a, p. 5). In Sonora, Mexico,
Flesch and Steidl (2007, p. 37)
documented dispersal distances ranging
from 1.1 to 19.2 km (0.7 to 11.5 mi).
Pygmy-owls are considered
nonmigratory throughout their range.
There are winter (November to January)
pygmy-owl locations from throughout
their historical range in Arizona
(University of Arizona 1995, pp. 1–2;
Snyder 2005, pp. 4–5; Abbate et al.
1999, pp. 14–17; 2000, pp. 12–13) and
also in Texas (Proudfoot 1996, p. 19;
Mays 1996, p. 14). These winter records
suggest that pygmy-owls are found
within their home ranges throughout the
year and that they do not migrate
seasonally. The pygmy-owl is primarily
diurnal (active during daylight) with
crepuscular (active at dawn and dusk)
tendencies.
The pygmy-owl is a perch-and-wait
hunter. It is largely a generalist with
regard to prey and diet. Oberholser
(1974, p. 451) indicated that the pygmyowl’s diet included lizards, large
insects, rodents, and birds (some as
large as the owl). In Texas, insects,
reptiles, birds, small mammals, and
amphibians, to a lesser extent, are eaten
by pygmy-owls (Proudfoot and Johnson
2000, p. 6). In Arizona, reptiles, birds,
small mammals, and insects have all
been recorded in the diet of the pygmyowl (Abbate et al. 1999, pp. 35–40).
Seasonal and annual variations in diet
occur throughout its range (Proudfoot
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and Johnson 2000, p. 6; Abbate et al.
1999, pp. 35–40).
The pygmy-owl is commonly mobbed
(harassed) by many species of
passerines, presumably in response to
being a regular predator on those
species (Proudfoot and Johnson 2000, p.
10; Abbate et al. 1999, pp. 25–26;
Hunter 1988, p. 1). The mobbing
behavior of birds can often aid in
locating a well hidden pygmy-owl, as
multiple individuals and species will
often participate in the mobbing and
identify the perch of the pygmy-owl.
The dark eye-spots on the back of the
pygmy-owl’s head may act to fend off
mobbing or increase predatory
efficiency by confusing prey (Heinrich
1987 in Proudfoot and Johnson 2000, p.
10).
Due to their small size and occurrence
in similar habitats as many of their
predators, pygmy-owls are preyed upon
by a variety of species. Documented and
likely predators in Texas and Arizona
include raccoons (Procyon lotor), great
horned owls (Bubo virginianus),
Cooper’s hawks (Accipiter cooperii),
Harris’ hawks (Parabuteo unicinctus),
western screech owls (Megascops
kennicottii), bull snakes (Pituophis
melanoleucus), and domestic cats (Felis
domesticus) (Abbate et al. 1999, p. 27;
Proudfoot and Johnson 2000, p. 10).
Pygmy-owls may be particularly
vulnerable to predation and other
threats during and shortly after fledging
(Abbate et al. 1999, p. 50). Lifespan has
been documented to be 7 to 9 years in
the wild (Proudfoot 2009b, p. 1) and 10
years in captivity (AGFD 2009, p. 1).
Summary of Information Pertaining to
the Five Factors Affecting the PygmyOwl Throughout Its Range
Section 4 of the Act (16 U.S.C. 1533)
and implementing regulations (50 CFR
424) set forth procedures for adding
species to, removing species from, or
reclassifying species on the Federal
Lists of Endangered and Threatened
Wildlife and Plants. Under section
4(a)(1) of the Act, a species may be
determined to be endangered or
threatened based on any of the
following five factors:
(A) The present or threatened
destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial,
recreational, scientific, or educational
purposes;
(C) Disease or predation;
(D) The inadequacy of existing
regulatory mechanisms; or
(E) Other natural or manmade factors
affecting its continued existence.
In making our 12-month finding on
the petition we considered and
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evaluated the best available scientific
and commercial information.
In considering whether the five
statutory factors in section 4(a) might
constitute threats, we must look beyond
the mere exposure of the species to the
factor and determine whether the
species responds to the factor in a way
that causes actual negative impacts to
the species. If there is exposure to a
factor, but no response, or only a
positive response, that factor is not a
threat. If there is exposure and the
species responds negatively, the factor
may be a threat and we then attempt to
determine how significant a threat it is.
If the threat is significant, it may drive
or contribute to the risk of extinction of
the species such that the species
warrants listing as threatened or
endangered as those terms are defined
by the Act. This does not necessarily
require empirical proof of a significant
threat. The combination of exposure and
some corroborating evidence of how the
species is likely impacted could suffice.
The mere identification of factors that
could impact a species negatively is not
sufficient to compel a finding that
listing is appropriate; we require
evidence that these factors are operative
threats that act on the species to the
point that the species meets the
definition of threatened or endangered
under the Act. A species may be
threatened or endangered based on the
intensity or magnitude of one operative
threat alone or based on the synergistic
effect of several operative threats acting
in concert.
Through our five-factor analysis, we
identified a number of factors negatively
impacting the pygmy-owl or its habitat.
To determine whether these impacts
individually or collectively rise to the
level of threats such that the pygmy-owl
is in danger of extinction throughout its
range, or likely to become so in the
foreseeable future, we first considered
whether these impacts to the subspecies
were causing long-term, range-wide,
population-scale declines in pygmy-owl
numbers, or were likely to do so in the
foreseeable future. Although some of
these impacts seem significant
individually, we found these impacts to
be localized in their effects, but not
placing the pygmy-owl in danger of
extinction throughout its range now or
in the foreseeable future. In other words,
the severe impacts were restricted to an
area that constitutes a relatively small
portion of the pygmy-owl’s range.
The detailed information we have on
impacts covers only about 27 percent of
the pygmy-owl’s range. For this area,
which includes Arizona and Texas in
the United States, and Sonora and
northern Sinaloa in Mexico, information
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describing the impacts to pygmy-owls
was relatively complete. For the
remaining 73 percent of the pygmy-owl
range in Mexico, information regarding
impacts to pygmy-owls was relatively
sparse. The best available scientific and
commercial information indicates that
the impacts to pygmy-owls in the
northern portion of their range are
severe. However, the best available
information indicates that pygmy-owls
in the southern portion of their range
remain common and that some of the
threats that are severe in the northern
portion of the species’ range appear to
be less severe or non-existent in the
southern portion. Thus we conclude
that pygmy owls are not threatened
throughout their range, or likely to
become so. The details supporting our
conclusion are found in the following
analysis.
Factor A: Present or Threatened
Destruction, Modification, or
Curtailment of Its Habitat or Range
For this factor, we evaluate available
information related to impacts to
pygmy-owl habitat throughout its range.
Our evaluation identified general
activities affecting or potentially
affecting pygmy-owl habitat that
included urbanization, nonnative
species invasions, fire, agricultural
development, wood cutting, improper
grazing, border issues, and off-highway
vehicle use. However, with the
exception of the United States and
Sonora, Mexico, detailed information
related to these activities is limited, and
we were unable to specifically evaluate
the effects of many of these activities for
much of the pygmy-owl’s range in
Mexico. The following discussion
presents the best available information
regarding these activities and their
effects to pygmy-owl habitat.
Urbanization
Increasing human populations result
in expanding urban areas. Urbanization
causes permanent impacts on the
landscape that potentially result in the
loss and alteration of pygmy-owl
habitat. Residential, commercial, and
infrastructure development replace and
fragment areas of native vegetation
resulting in the loss of available pygmyowl habitat and habitat connectivity
needed to support pygmy-owl dispersal
and metapopulation function.
Increasing human populations require
additional water, and increasing water
consumption can reduce available
surface and ground water needed to
support pygmy-owl and pygmy-owl
prey habitats. Added human presence
on the landscape can potentially lead to
increased pygmy-owl mortality through
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introduced predators, collisions, etc.
The following discussion presents the
available information related to pygmyowl habitat impacts associated with
urbanization.
Human population growth results in
the expansion of urbanization (Travis et
al. 2005, p. 2). Arizona’s population
increased by 394 percent from 1960 to
2000, and was second only to Nevada as
the fastest growing State during this
timeframe (Social Science Data Analysis
Network (SSDAN) 2000, p. 1). Since
1990, Arizona’s population has grown
by 44 percent. From 1960 to 2000,
population growth rates in Arizona
counties where the pygmy-owl occurs,
or recently occurred, have varied by
county, but all are increasing: Maricopa
(463 percent); Pima (318 percent); Pinal
(54 percent); and Santa Cruz (355
percent) (SSDAN 2000).
Urban expansion and human
population growth trends in Arizona are
expected to continue into the future.
The Maricopa-Pima-Pinal County areas
of Arizona are expected to grow by as
much as 71 percent in the next 15 years,
creating rural-urban edge effects across
thousands of acres of pygmy-owl habitat
(AIDTT 2000, p. 10; BLM files-Lands
Livability Initiative). In another
projection, the Arizona population is
expected to more than double within
the next 20 years, compared to the 2000
population estimate (U.S. Census
Bureau 2005, p. 1). Many cities and
towns within the historical distribution
of the pygmy-owl in Arizona already
experienced substantial growth during
the 8-year time span from 2000 to 2008:
Town of Carefree (30.5 percent); Casa
Grande (56 percent); Town of Cave
Creek (44.2 percent); City of Eloy (22.3
percent); City of Florence (20.3 percent);
City of Mammoth (45 percent); Town of
Marana (139.9 percent); Town of Oro
Valley (32.5 percent); and the Town of
Sahuarita (507.3 percent) (U.S. Census
Bureau 2008, pp. 1–4).
This population growth has spurred a
significant increase in urbanization and
development in these areas. Regional
development is predicted to be high in
certain areas within the distribution of
the pygmy-owl in Arizona. In particular,
a wide area from the international
border in Nogales, through Tucson,
Phoenix, and north into Yavapai County
(called the Sun Corridor ‘‘Megapolitan’’
Area) is predicted to have 8 million
people by 2030, an 82.5 percent increase
from 2000 (Gammage et al. 2008, pp. 15,
22–23). If build-out occurs as expected,
it will encompass a substantial portion
of the current and historical distribution
of the pygmy-owl in Arizona.
Development pressure across Arizona
has slowed due to the recent economic
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downturn and decline in the housing
market. However, development will
likely continue in the future, although
perhaps at a slower pace than in the
earlier part of this century. We also
recognize that economic trends are
difficult to predict into the future. The
most recent draft Pinal County
Comprehensive Plan (February 2009)
acknowledges that the county is in the
middle of the Sun Corridor Megapolitan
and proposes four shorter-term growth
areas in defining where development
will likely occur over the next decade,
but does not discourage growth outside
of these areas (Pinal County
Comprehensive Plan 2009, p. 109).
Areas within two of the four growth
areas (West Pinal and Red Rock) support
historically occupied and recently
occupied areas.
Because most of the pygmy-owl
habitat in Texas occurs on private ranch
lands, the impact of habitat loss and
fragmentation of the remaining pygmyowl habitat due to urbanization is
greatly reduced. Some housing, ranch
facilities, roadways, and utilities will
undoubtedly be constructed with
changing ranch plans, and this may
affect individual pygmy-owl territories.
However, the overall impact to pygmyowl habitat from current rates of
urbanization in Texas is much less than
that in Arizona and parts of Mexico.
In Mexico, the greatest increases in
population have occurred mostly in
coastal resort areas, State capitals, and
along the United States-Mexico border.
In the Sonoran Desert Ecoregion of
Mexico (a relatively homogeneous
ecological area defined by similarity of
climate, landform, soil, potential natural
vegetation, hydrology, or other
ecologically relevant variables), the
human population nearly doubled
between 1970 and 1990, to a total
population of 6.9 million (Gorenflo
2002, p. 13). The Sonoran capital,
Hermosillo, grew by 116 percent. When
considering urban growth within
individual biotic communities, the
human population more than doubled
in three of the seven major
biogeographic communities of Mexico
(Arizona Upland and Lower Colorado
River Valley, Plains of Sonora, and
Magdalena Plain) (Gorenflo 2002, p. 28),
all of which provide important pygmyowl habitat.
The United States-Mexico border
region has a distinct demographic
pattern of permanent and temporary
development related to warehouses,
exports, and other border-related
activities, and patterns of population
growth in this area of northern Mexico
have been accelerated relative to other
Mexican States (Pineiro 2001, pp. 1–2).
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This focuses development, and potential
barriers or impediments to pygmy-owl
movements, in a region that is important
for pygmy-owl metapopulation support
and other movements such as dispersal.
The Arizona-Sonora border region’s
population growth is expected to reach
2.1 million (Walker and PavlakovichKochi 2003, p. 1) in an area that will
affect cross-border movement by pygmyowls and other important population
linkages needed to support the pygmyowl metapopulation structure. Based on
1990 human population numbers, the
land cover types currently most
valuable to the pygmy-owl—Mesquite
Bosque and Palo Verde-Mixed Cactus—
were the most heavily human-populated
in the Sonoran Desert Ecoregion. The
Mesquite Bosque type makes up 8.2
percent of the area, but supports 10.4
percent of the human population.
Similarly, the Palo Verde-Mixed Cactus
type covers 29 percent of the area, but
supports 49.4 percent of the population
(Gorenflo 2002, p. 28).
Human activity, most notably in the
past century, has dramatically altered
the landscape of the Arizona-Sonora
border, affecting both the quantity and
quality of its ecological resources.
Urbanization not only reduces the
amount of open space, but impacts the
biological value of areas (Walker and
Pavlakovich-Kochi 2003, p. 3). The
Sonoran border population has been
increasing faster than that State’s
average and faster than Arizona’s border
population; between 1990 and 2000, the
population in the Sonoran border
municipios increased by 33.4 percent,
compared to Sonora’s average (21.6
percent) and the average increase of
Arizona’s border counties (27.8
percent). Urbanization has increased
habitat conversion and fragmentation,
which, along with immigration,
population growth, and resource
consumption, were ranked as the
highest threats to the Sonoran Desert
Ecoregion (Nabhan and Holdsworth
1998, p. 1).
Urbanization has also affected pygmyowl habitat in other parts of Mexico.
Trejo and Dirzo (2000, p. 133) indicate
that areas of dry subtropical forests,
important habitat for pygmy-owls in
southwestern Mexico, have been used
by humans through time for settlement
and various other activities. The longterm impact of this settlement has
converted these dry subtropical forests
into shrublands and savannas lacking
large trees, columnar cacti, and cover
and prey diversity that are important
pygmy-owl habitat elements Trejo and
Dirzo (2000, p. 134) state that in Mexico
dry tropical forest is the major type of
tropical vegetation in the country,
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covering over 60 percent of the total
area of tropical vegetation. According to
official governmental maps, about 8
percent (approximately 160,000 square
km (61,776 square mi)) of this forest
remained intact by the late 1970s, and
an assessment made at the beginning of
the present decade suggested that 30
percent of these tropical forests have
been altered and converted to
agricultural lands and cattle grasslands.
The remaining forests are restricted to
steep slopes where it is not likely that
land will be cleared for additional
agricultural or development purposes
(Allnutt 2001, p.3). However, the
information about the current actual
extension and condition of dry tropical
forests in Mexico is unclear due to
confusion in their classification and
difficulty using remote sensing to
delineate intact dry forest (Allnutt 2001,
p. 3). The best available information
indicates that there are still expanses of
dry tropical forest along the Pacific
coast in Mexico, including some areas
below 1,200 m (4,000 ft) where pygmyowls are found, but there has been loss
of this forest type throughout Mexico.
The actual effects of urbanization on
biodiversity are many and mutually
reinforcing, including the aggravation of
the ‘‘urban heat island effect’’; the
channelization or disruption of riverine
corridors; the proliferation of exotic
species; the killing of wildlife by
automobiles, toxins, and pets; and the
fragmentation of remaining patches of
natural vegetation into smaller and
smaller pieces that are unable to support
viable populations of native plants or
animals (Ewing and Kostyack 2005, pp.
1–2; Nabhan and Holdsworth 1998, p.
2). Human-related mortality (e.g.,
shooting, collisions, and predation by
pets) increases as urbanization increases
(Banks 1979, pp. 1–2; Churcher and
Lawton 1987, p. 439). The above
statements, while general in their
nature, point out the vulnerability of
habitats that support pygmy-owls and
the impacts that urbanization can have
on the extent and quality of available
habitat. We would expect these types of
impacts in areas that have experienced
or are experiencing urban growth in or
near pygmy-owl habitats. Not all areas
in the United States and Mexico are
experiencing this type of growth,
especially in the southern portion of the
pygmy-owl’s range.
Development of roadways and their
contribution to habitat loss and
fragmentation is a particularly
widespread impact of urbanization
(Nickens 1991, p. 1). Data from Arizona
and Mexico indicate that roadways and
other open areas lacking cover affect
pygmy-owl dispersal (Flesch and Steidl
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2007, pp. 6–7; Abbate et al. 1999, p. 54).
Nest success and juvenile survival were
lower at pygmy-owl nest sites closer to
large roadways, suggesting that habitat
quality may be reduced in those areas
(Flesch and Steidl 2007, pp. 6–7).
Currently, most roadways in Sonora
are relatively narrow. However, the
Sonoran government is starting to
implement plans to build new highways
and other infrastructure improvements.
Governor Bours of Sonora formed the
Sonoran Strategic Projects Operator, in
conjunction with other investors, to
carry out the construction of highway
improvements (Wild Sonora 2009, p. 2).
Of specific concern related to pygmyowl impacts is the recent improvement
of the road between Saric, in the upper
Rio Altar valley, and Sasabe, in the
heart of the distribution of the pygmyowl in northern Sonora. Instead of just
paving the existing Altar/Sasabe road, a
new highway was constructed resulting
in an increase of habitat impacts and
fragmentation (Wild Sonora 2009, p. 2).
Another development project proposed
for northern Sonora is the Quitovac
toxic waste dump south of Organ Pipe
Cactus National Monument that could
accept up to 45,000 tons of toxic waste
per year (Wild Sonora 2009, p. 7). The
proposed site for this project is located
in the vicinity of a rare spring in this
very arid region that supports pygmyowl habitat. There are documented
pygmy-owls nesting at Quitovac (Flesch
2003, pp. 40–41). While this project is
currently on hold, it represents the
potential for impacts to pygmy-owls
related to development and
urbanization in Sonora.
Significant human population
expansion and urbanization in the
Sierra Madre foothill corridor may
represent a long-term risk to pygmyowls in northeastern Mexico. In Texas,
the pygmy-owl occurred in good
numbers until approximately 90 percent
of the mesquite-ebony woodlands of the
Rio Grande delta were cleared in 1910–
1950 (Oberholser 1974, p. 452). Habitat
removal in northeastern Mexico is
widespread and nearly complete in
northern Tamaulipas (Hunter 1988, p.
8). The pygmy-owl metapopulation
structure is threatened by ongoing loss
and fragmentation of habitat in this area.
Urbanization has the potential to
permanently alter the last major
landscape linkage between the pygmyowl population in Texas and those in
northeastern Mexico (Tewes 1992, pp.
28–29).
With regard to Mexico, for those areas
outside of Sonora and northeastern
Mexico discussed above, human
population growth in Sinaloa, Nayarit,
Colima, and Jalisco are relatively slow
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compared to Sonora. The Sinaloan
population grew at a rate of 0.9 percent
over the last decade. The population in
Nayarit grew at a rate of 1.8 percent over
the last decade. The Jalisco population
grew by 1.6 percent per year during
2000–2010. Colima, one of the smallest
States in Mexico, has a total population
of approximately 650,500 and grew
annually at a rate of 1.9 percent over the
last decade. These areas of Mexico are
not experiencing the high growth rates
of Sonora, and likely will not have the
concurrent spread of urbanization in the
foreseeable future. In addition, most of
the growth is taking place in the large
cities, and not the rural areas of these
countries (http:www.citypopulation.de/
Mexico-Cities.html). Also, some of the
large cities of the southern Mexican
States, such as Guadalajara in Jalisco
´
and Morelia in Michoacan, are not
within the range of the pygmy-owl, so
their growth would not be affecting
pygmy-owl habitat. The rural areas
likely contain the remaining habitat for
the pygmy-owl. It is reasonable to
assume that slow or stagnant population
growth will result in fewer
developments and infrastructure
projects, such as new highways, or
destruction and fragmentation of habitat
on a landscape scale. The impacts
associated with urbanization are,
therefore, much reduced and less severe
in this portion of the pygmy-owl’s
range. While the magnitude of the
impacts associated with urbanization
are significant in Arizona and northern
Mexico, we would expect these impacts
to be much reduced in the remaining 73
percent of the pygmy-owl’s range in
Mexico and we expect these impacts to
remain less significant in this part of its
range into the foreseeable future because
of the difference in population growth.
Nonnative Invasive Species
The invasion of nonnative vegetation,
particularly nonnative grasses, has
altered the natural fire regime over the
Sonoran portion of the pygmy-owl
range. As a result, fire has become a
significant threat to the native
vegetation of the Sonoran Desert. Esque
and Schwalbe (2002, pp. 180–190)
discuss the effect of wildfires in the
Arizona Upland and Lower Colorado
River subdivisions of Sonoran
desertscrub, which comprise the
primary portions of the pygmy-owl’s
range within Sonoran desertscrub. The
widespread invasion of nonnative
annual grasses appears to be largely
responsible for altered fire regimes that
have been observed in these
communities, which are not adapted to
fire (Esque and Schwalbe 2002, p. 165).
In areas comprised entirely of native
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species, ground vegetation density is
mediated by barren spaces that do not
allow fire to carry across the landscape.
However, in areas where nonnative
species have become established, the
fine fuel load is continuous, and fire is
capable of spreading quickly and
efficiently (Esque and Schwalbe 2002, p.
175). Nonnative annual plants prevalent
within the Sonoran range of the pygmyowl include Bromus rubens and B.
tectorum (brome grasses) and Schismus
spp. (Mediterranean grasses) (Esque and
Schwalbe 2002, p. 165). Brassica
tournefortii (Sahara mustard) is an Old
World forb that can cover 100 percent
of the ground under certain conditions
(ASDM 2009, p. 1). In 2006, fires that
burned thousands of acres of Sonoran
desertscrub in southwestern Arizona
had Sahara mustard as the primary fuel.
However, the nonnative species that is
currently the greatest threat to
vegetation communities in Arizona and
northern Sonora, Mexico is the
perennial Pennisetum ciliare
(buffelgrass), which is prevalent and
increasing throughout much of the
Sonoran range of the pygmy-owl
(Burquez and Quintana 1994, p. 23; Van
Devender and Dimmit 2006, p. 5).
Buffelgrass is an Indo-African grass
introduced to Mexico between 1940 and
1960 (Burquez et al. 1998, p. 25). The
distribution of this grass has been
supported and promoted by
governments on both sides of the United
States-Mexico border as a resource to
increase range productivity and forage
production. Buffelgrass is first
established by stripping away the native
desertscrub and thornscrub (Franklin et
al. 2006, p. 69). Following
establishment, it fuels fires that destroy
Sonoran desertscrub, thornscrub, and, to
a lesser extent, tropical deciduous
forest; the disturbed areas are quickly
converted to open savannas composed
entirely of buffelgrass. Buffelgrass is
now fully naturalized in most of Sonora,
southern Arizona, and some areas in
central and southern Baja California
(Burquez-Montijo et al. 2002, p. 131),
and now commonly spreads without
human cultivation (Arriaga et al. 2004,
pp. 1509–1511; Perramond 2000, p. 131;
Burquez et al. 1998, p. 26).
However, buffelgrass is adapted to
dry, arid conditions and does not grow
in areas with high rates of precipitation
or high humidity, above elevations of
1,265 m (4,150 ft), and in areas with
freezing temperatures. Areas that
support pygmy-owls south of Sonora
and northern Sinaloa typically are
wetter and more humid, and the best
available information does not indicate
that buffelgrass is invading the southern
portion of the pygmy-owl’s range.
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Buffelgrass is most often located on
steep, rocky, south-facing slopes, with
poor soil development (Van Devender
and Dimmitt 2006, pp. 25–26). Surveys
completed in Sonora and Sinaloa in
2006 noted buffelgrass was present in
Sonora and northern Sinaloa, but the
more southerly locations were noted as
sparse or moderate (Van Devender and
Dimmitt 2006, p. 7). This was in
comparison to northerly sites in Sonora
that were rated as dense with
buffelgrass. As such, this nonnative
species only significantly affects a
portion of the pygmy-owl’s range. The
best available information indicates that
buffelgrass is not significantly affecting
areas in Mexico beyond Sonora, and
northern Sinaloa.
Buffelgrass is not only fire-tolerant
(unlike native Sonoran Desert plant
species), but is actually fire-promoting
(Halverson and Guertin 2003, p. 13).
Invasion sets in motion a grass-fire cycle
where nonnative grass provides the fuel
necessary to initiate and promote fire.
Nonnative grasses recover more quickly
than native grass, tree, and cacti species
and cause a further susceptibility to fire
(D’Antonio and Vitousek 1992, p. 73;
Schmid and Rogers 1988, p. 442). While
a single fire in an area may or may not
produce long-term reductions in plant
cover or biomass, repeated wildfires in
a given area, due to the establishment of
nonnative grasses, are capable of
ecosystem type-conversion from native
desertscrub to nonnative annual
grassland, and render the area
unsuitable for pygmy-owls and other
native wildlife due to the loss of trees
and columnar cacti and reduced
diversity of cover and prey species
(Brooks and Esque 2002, p. 336).
Buffelgrass competes with neighboring
native species for space, water, and
nutrients (Halverson and Guertin 2003,
p. 13; Williams and Baruch 2000, pp.
128–135; D’Antonio and Vitousek 1992,
pp. 68–72). Buffelgrass conversion is
associated with increased soil erosion
and changes in nutrient dynamics and
primary productivity (Abbot and
McPherson 1999, p. 3). These changes
make it more difficult for native
vegetation to reestablish, even if the
conversion process or fires are
discontinued (Franklin et al. 2006, p.
69; Rogers and Steele 1980, pp. 17–18).
Within the past 15 years, the
establishment of nonnative grasslands
has been identified as the most serious
threat to the biological diversity of the
Sonoran Desert (Burquez and Quintana
1994, p. 23). Economic subsidies from
the State of Sonora and low-interest
loans from banks made funds available
for more widespread plantings of
buffelgrass in the 1980s (Camou-Healy
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1994). By 1997, more than 1 million ha
(2.5 million ac) of desertscrub and
thornscrub (both communities occupied
by the pygmy-owl) had been cleared in
central Sonora to plant buffelgrass, and
more than 2 million ha (5 million ac)
were scheduled for future vegetation
conversion (Burquez and Quintana
1994, p. 23; Johnson and Navarro 1992,
p. 118), often as part of government
programs to support the ranching
industry (Van Devender et al. 1997, p.
3). Researchers during this time period
predicted that, if not halted, this
practice of buffelgrass planting will
permanently change the landscape of
the Sonoran desert and deplete its
associated biological diversity (Burquez
and Quintana 1994, p. 23). Also, given
the government subsidies to establish
exotic grasslands in order to maintain
large cattle herds, and to support
marginal cattle ranching, it is less likely
that control measures will be
implemented, and the desertscrub and
thornscrub in Sonora will probably be
replaced in the near term by ecosystems
with significantly lower species
diversity and reduced structural
complexity (Burquez and MartinezYrizar 1997, p. 387).
More recent figures indicate that this
is indeed occurring, with buffelgrass
present in more than two-thirds of
Sonora, and 1.6 million ha (4 million ac)
having been deliberately cleared and
seeded with the species (BurquezMontijo et al. 2002, p. 132). A 2006
publication estimates that 1.8 million ha
(4.5 million ac) have been converted to
buffelgrass in Sonora, and that between
1990 and 2000, there was an 82 percent
increase in buffelgrass coverage
(Franklin et al. 2006, pp. 62, 66).
Buffelgrass pastures have doubled in
area in Sonora approximately every 10
years since 1973 (Franklin et al. 2006,
p. 67) and the conversion to buffelgrass
is expected to continue into the
foreseeable future.
It is not only Sonoran desertscrub
communities in Sonora and northern
Sinaloa that are impacted by the spread
of buffelgrass. Another unique
vegetation community in this region,
dry subtropical forests, are being lost
and fragmented due to the planting of
buffelgrass in association with cattle
ranching, which results in vast tracts of
forest being removed and replaced by
buffelgrass (Allnut et al. 2001, pp. 3–4).
Buffelgrass invasion in the United
States is such an urgent and significant
issue that the Governor of Arizona, and
nearly all southern Arizona
municipalities and agencies have joined
together to address the issue. The
Governor formed the Arizona Invasive
Species Advisory Council in 2005, and
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the Southern Arizona Buffelgrass
Working Group developed the Southern
Arizona Buffelgrass Strategic Plan in
2008 (Buffelgrass Working Group 2008)
in order to coordinate the control of
buffelgrass. Because of its negative
impacts to native ecosystems,
buffelgrass was declared a noxious weed
by the State of Arizona in March 2005.
It is not currently known whether these
programs will be successful in
controlling buffelgrass invasion.
The impacts of buffelgrass
establishment and invasion are
substantial for the pygmy-owl in the
United States and Sonora because
conversion results in the loss of all
important habitat elements, particularly
columnar cacti and trees that provide
nest sites. Buffelgrass invasion and the
subsequent fires eliminate most
columnar cacti, trees, and shrubs of the
desert (Burquez-Montijo et al. 2002, p.
138). This elimination of trees, shrubs,
and columnar cacti from these areas is
a significant negative impact and
potentially a threat to the survival of the
pygmy-owl in the northern portion of its
range, as these vegetation components
are necessary for roosting, nesting,
protection from predators, and thermal
regulation. Because tree canopy cover is
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an important pygmy-owl habitat feature,
the fact that buffelgrass fires reduce the
number of tree-dominated patches and
the recruitment opportunities for those
native species dependent on them [such
as saguaros] (Burquez and Quintana
1994, p. 11), is significant. Franklin et
al. (2010, p. 7) report significant
changes in vegetation structure as a
result of creating buffelgrass pastures for
grazing. There were 90 percent fewer
trees and shrubs of the size used by
pygmy-owls (2 to 5 m (6 to 15 ft) tall)
in buffelgrass pastures as compared to
native vegetation communities. Loss of
diversity and availability of prey species
due to conversion are also detrimental
(Franklin et al. 2006, p. 69; Avila
Jimenez 2004, p. 18; Burquez-Montijo et
al. 2002, pp. 130, 135).
Some information we received from
the public downplays the significance of
the conversion of Sonoran desertscrub
to buffelgrass savannas on pygmy-owl
habitat by stating that there is no
indication that the conversion is
occurring in areas occupied by the
pygmy-owl (Johnson and Carothers
2003, pp. 6–7). However, when
compared to the maps of current and
predicted buffelgrass invasion in Sonora
found in Arriaga et al. (2003, Figure 1),
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the distribution of pygmy-owl locations
from Flesch (2003, Figure 2), AGFD
(2008a, p. 1), and Westland Resources
(2008, Figure 4), as well as the known
pygmy-owl locations and the
documented occurrence of buffelgrass in
Tucson, Avra Valley, Altar Valley,
Organ Pipe Cactus National Monument,
Pinal County, the Tohono O’odham
Nation, and Sonora and northern
Sinaloa show that there is almost 100
percent overlap in the areas occupied by
pygmy-owls and the areas under
greatest threat from buffelgrass invasion.
One of the principle reasons that
nonnative plants pose such a significant
negative impact on the pygmy-owl in its
northern range, and the native plant
communities on which they depend, is
because few, if any, reasonable methods
currently exist to control the ongoing
invasion of these plants or to remediate
areas where they are already
established. Mechanical removal,
herbicides, and fire have all been tested
for their effectiveness in control of this
nonnative grass. However, none have
proven effective at the scale of the
current invasion.
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In Texas and other portions of the
pygmy-owl’s range in the United States,
such as semi-desert grasslands, invasive
species and fire are not as significant in
their impact because the vegetation
communities in these areas are adapted
to periodic fire. However, while fire
may not be a primary issue, nonnative
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species can cause other effects to
pygmy-owl habitat elements. For
example, in Texas, studies indicate that
the spread and prevalence of the
nonnative grass, Bothriochloa
ischaemum (King Ranch bluestem),
results in this grass dominating native
grasses, forbs, and endemic species,
thus decreasing plant and animal
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species diversity and altering the
vegetative structure of the community
(Davis 2011, p. 4). It is not known if
these changes in plant community
structure affect pygmy-owls.
The best available scientific and
commercial information, as presented in
the discussion above, leads us to
conclude that conversion of Sonoran
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desertscrub to nonnative plant pastures
composed of buffelgrass, and the
subsequent change in the fire regime,
has resulted in the loss of large areas of
pygmy-owl habitat in the northern range
of the pygmy-owl, is negatively
impacting the remaining areas of
pygmy-owl habitat in the Sonoran
desert and tropical thornscrub/dry
deciduous forest communities of
Arizona, Sonora, and northern Sinaloa,
and is expected to continue to do so in
the foreseeable future. Other areas in
Texas and the United States, such as
semidesert grassland, are not as affected
by buffelgrass and subsequent changes
in fire behavior, but may be invaded by
other nonnative species. However, the
effect, if any, on pygmy-owls, has not
been studied.
In contrast to the severity of
buffelgrass invasion as a significant
negative impact to the pygmy-owl in the
northern portions of its range, it appears
to have less impact or no impact at all
further south. The area in Mexico that
is susceptible to buffelgrass invasion
and planting represents only just over
22 percent of the pygmy-owl’s range.
The magnitude of the impact diminishes
in the southern portion of the range
where buffelgrass has not been reported
in the dry tropical forests, which
comprise the majority of pygmy-owl
habitat in the southern portion of its
range. In addition, buffelgrass is not
likely to invade and persist in these
areas in the foreseeable future because
it is adapted to dry, arid savannahs and
grasslands in its native Africa (Burquez
et al. 1998, p. 25). The elevational
conditions, canopy coverage, and
precipitation patterns of the dry tropical
forest communities are not as suitable
for the establishment of buffelgrass as
the arid desert and semi-desert
vegetation communities (Arriaga et al.
2004, pp. 1508–1510.). The best
available scientific and commercial
information suggests that buffelgrass
invasion should not be an issue in the
southern portions of the pygmy-owls
range, nor should it become an issue in
the future.
Agricultural Production and Wood
Harvesting
Agricultural development and wood
harvesting can result in substantial
impacts to the availability and
connectivity of pygmy-owl habitat.
Conversion of native vegetation
communities to agricultural fields or
pastures for grazing has occurred within
historical pygmy-owl habitat in both the
United States and Mexico, and not only
removes existing pygmy-owl habitat
elements, but also can affect the longterm ability of these areas to return to
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native vegetation communities once
agricultural activities cease. Wood
harvesting has a direct effect on the
amount of available cover and nest sites
for pygmy-owls and is often associated
with agricultural development. Wood
harvesting also occurs to supply
firewood and charcoal, and to provide
material for cultural and decorative
wood carvings. While we do not have
detailed information regarding the
impacts of agricultural development and
wood harvesting for all areas within the
range of the pygmy-owl, the following
provides a discussion of the extent of
the impacts from these activities for
areas for which we do have sufficient
information.
The extent of agricultural
development and woodcutting as a
current or ongoing impact to pygmy-owl
habitat differs between the United States
and Mexico. For example, in the United
States, habitat loss and conversion due
to agricultural development is more of
a historical issue because less area is
being used currently for agriculture, and
wood cutting is primarily for personal,
rather than commercial use. However,
impacts to pygmy-owl habitat from
historical agricultural use and wood
harvesting are still evident. The
vegetation and soils of many valleys in
the Sonoran Desert were shaped by the
periodic flooding of dynamic wash
systems, which partially recharged a
shallow, fluctuating groundwater table.
Because of agricultural development,
these valleys no longer experience these
defining processes and there has been a
permanent loss of meso- and xeroriparian habitat (Jackson and Comus
1999, pp. 233, 249). These riparian
habitats are important pygmy-owl
habitat, especially within drier upland
vegetation communities like Sonoran
desertscrub and semi-desert grasslands.
In Arizona, although new agricultural
development is limited and is expected
to remain limited in the foreseeable
future, the effects to historical habitat
are still evident. Jackson and Comus
(1999, pp. 249–250) describe the longterm effects of agricultural development
on native vegetation communities, ‘‘The
groundwater has been mined, river
flows have been relocated, tributaries
have been channelized, and smaller
waterways are blocked by roads or the
canals of the Central Arizona Project.
Soil-surface characteristics have been
greatly altered by field leveling and
irrigation ditches. Compounding these
large-scale changes, soil in some areas
has increased salinity, pesticide
residues, or loss of physical structure
due to repeated tillage, soil compaction,
and irrigation.’’ There have been
important biological losses and
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introductions as well. Seed sources of
native plants in these old agricultural
fields are now rare. Natural regeneration
of many of the old agricultural fields is
unlikely because they are no longer near
to a native seed source (Jackson and
Comus 1999, pp. 243–247, 250).
It is not known to what extent the loss
of certain pollinators, predators,
detritivores (organisms that obtain
nutrients by consuming decomposing
organic matter), cryptogamic crusts (soil
with crusts formed by an association of
algae, mosses, and fungi; such crusts
stabilize desert soil, retain moisture, and
protect germinating seeds), mycorrhizae
(a fungus that grows in a symbiotic
association with plant roots), etc., as
well as the addition of exotic species,
will have on recovery of habitat.
Because of these profound changes, we
believe that habitat recovery, either by
natural succession or through various
attempts at ecological restoration, will
be very limited (Jackson and Comus
1999, p. 250). The significance of this
lies in the fact that many acres of
pygmy-owl habitat have been lost to
agricultural development, especially
along valley bottoms and drainages that
were important for pygmy-owls as they
supported higher quality meso- and
xero-riparian habitats. A well-known
example of this is the huge mesquite
bosque (woodland) south of Tucson on
the San Xavier District of the Tohono
O’odham Nation that comprised oldgrowth mesquites supporting cavities
for pygmy-owl nests, adequate cover,
and prey diversity, and which was lost
due to groundwater pumping and
diversion for agriculture and urban
growth (Stromberg 1993, pp. 117–119).
Mesquite bosques provide important
pygmy-owl habitat. The viability of
these bosques is dependent upon the
ability of native trees, like mesquite, to
reach the water table with their taproots.
Only then can they grow to sizes that
provide habitat for pygmy-owls. Even
when abandoned and left to return to
their natural state, there has been such
extensive alteration of soils, drainage
patterns, and contamination that these
impacted bosques are unlikely to ever
regain the historical habitat values.
Restoration of old agricultural areas
often meets with either limited success
or failure.
Historically, agriculture in Sonora,
Mexico, was restricted to small areas
with shallow water tables, but it had,
nonetheless, seriously affected riparian
habitats by the end of the nineteenth
century. Large-scale agriculture was
introduced in the 1940s, with the
construction of dams in the Rio Yaqui
and Rio Mayo watersheds. By the late
1970s, the delta regions and alluvial
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plains of these rivers were almost
entirely converted to field crops. Huge
expanses of natural vegetation had been
cleared. The vast mesquite forests of the
Llanos de San Juan Bautista in the
plains of the Rio Sonora disappeared
with the development of the Costa De
Hermosillo irrigation district. In the Rio
Mayo and Rio Yaqui coastal plains,
nearly one million ha (2.5 million ac) of
mesquite, cottonwood, and willow
riparian forests and coastal thornscrub
disappeared after dams upriver started
to operate (Burquez and Martinez-Yrizar
2007, p. 543). In 1980, a national food
system was initiated and the total area
under cultivation in northern Mexico
increased significantly (Stoleson et al.
2005, p. 59).
Based upon the amount of area
currently in irrigated agriculture,
Sonora, with 530,000 ha (1.3 million
ac), ranks second among the States in
Mexico to Sinaloa (747,800 ha (1.85
million ac)), a State which is also
occupied by pygmy-owls. The area
equipped for agricultural irrigation in
Sonora is 668,900 ha (1.65 million ac),
resulting in the potential future loss of
approximately 139,000 ha (343,000 ac)
of natural vegetation communities
(AQUASTAT 2007, p. 2) if these areas
are developed for agriculture. Other
Mexican States within the range of the
pygmy-owl show similar potential for
habitat loss. For example, in
Tamaulipas, area under irrigation
increased from 174,400 to 494,472 ha
(431,000 to 1.22 million ac) between
1998 and 2004, with an area of 668,872
ha (1.65 million ac) equipped for
´
irrigation. Michoacan supports 24,900
ha (61,500 ac) of irrigated lands with a
potential infrastructure for 222,800
additional ha (550,600 ac). Although the
amount of land converted to agriculture
seems to be on the increase, we do not
know where these areas are in relation
to pygmy-owl habitat. Dry tropical
forests on steeper slopes are not likely
to be used for agricultural production.
In addition, agricultural development in
the States of Colima, Jalisco, Nayarit,
and Nuevo Leon had substantial
decreases in the amount of irrigated
lands over the same period. Colima
dropped from 64,100 ha (158,394 ac) to
37,800 ha (93,406 ac), Jalisco went from
161,600 ha (399,322 ac) to 95,600 ha
(236,233 ac), Nayarit decreased from
55,400 ha (136,896 ac) to 43,200 ha
(106,749 ac), and Nuevo Leon dropped
from 143,000 ha (353,361 ac) to 32,484
ha (80,270 ac). These numbers indicate
that continuing destruction of habitat
for agricultural production is not
occurring with the same intensity
throughout the range of the pygmy-owl,
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and may be declining in large parts of
its southern range (AQUASTAT 2007, p.
2).
Agricultural development is declining
in some parts of the pygmy-owl’s range,
but seems concentrated in the northern
portion of the range. In certain localities
in northwestern Mexico, especially
Sonora, it has remained the same and
even increased over the past few
decades. In the Sonoyta Valley of
Sonora flanking Organ Pipe Cactus
National Monument across the United
States-Mexico border, cropland
quadrupled in extent between 1977 and
1987, due in part to governmentsupported agricultural development.
Proximity to U.S. fruit and vegetable
markets, inexpensive labor, good quality
water, and government agency interest
in increased fruit and vegetable crops in
the area mean that agricultural
production and the associated descent
of groundwater levels will likely
continue in the future (Nabhan and
Holdsworth 1998, p. 36). Some
scientists surveyed noted that clearing
for agriculture was becoming more
severe in portions of the Lower
Colorado River Valley, Central Gulf
Coast, and Viscaino. Current Sonoran
Desert cropland is most extensive in the
border municipality of Mexicali and the
extreme southern end of the Sonoran
Desert where most municipalities have
from one-quarter to three quarters of
their land surface as cropland. The
central section around Hermosillo,
Sonora, is 15 to 25 percent cropland,
and the rest of the area is less than 15
percent (Nabhan and Holdsworth 1998,
p. 36). However, these figures do not
include the millions of hectares (acres)
of abandoned agricultural land. While
not all the area converted for agriculture
was or could be suitable pygmy-owl
habitat, agricultural development has
typically occurred along river bottoms
and other drainages that support
important riparian habitat for pygmyowls (Flores-Villela and Fernandez
1989, p. 2). Additionally, associated
habitat fragmentation exacerbates the
actual impacts to available pygmy-owl
habitat through loss of habitat
connectivity (Stoleson et al. 2005, p. 60;
Saunders et al. 1991, pp. 23–24).
Prescribed burning to reduce
mesquite invasion into rangelands
represents another potential threat to
pygmy-owl habitat associated with
agriculture. In general, improved
grassland health adjacent to pygmy-owl
habitat should benefit pygmy-owls
through improved hydrology and
enhance prey habitat. However, if
woodlands providing important pygmyowl habitat are not protected during
prescribed burns, impacts to pygmy-owl
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habitat can be significant due to the loss
of nest structures, predator and thermal
cover, and prey habitat. For example, in
Texas, two prescribed burns over the
past 3 years have consumed 1,200 to
1,600 ha (3,000 to 4,000 ac) respectively,
including areas that supported natural
pygmy-owl nests, as well as pygmy-owl
nest boxes (Proudfoot 2011b, p. 1).
Other documented fires on the King
Ranch consumed from several hundred
up to 3,200 ha (8,000 ac) over this same
time period (Caller 2009, NOAA 2011,
Texas-Fire.com 2011, Firerescue 2008).
While the loss of woodlands to fire is
often a temporary impact, it can take
many years for trees to reach adequate
size to once again support cavities used
for nesting by pygmy-owls.
Mesquite harvesting also has negative
impacts on pygmy-owl habitat.
Mesquite wood is a valuable
commodity. Historically in Arizona,
mesquite trees have been harvested for
decades. In the late 1800s through the
early 1900s, Arizona saw large-scale
harvesting for fuel and for mining.
Fuelwood cutting once had a major
impact on the riparian forests, mesquite
thickets, and evergreen woodlands near
most of southeastern Arizona’s major
cities and mining centers (Bahre 1991,
p. 143). This whole-scale harvest may
explain the scarcity of riparian trees in
early (1890) photographs of southern
rivers such as the San Pedro (Stromberg
1993, p. 119). In the Sonoran Desert of
Mexico, the mesquite tree is being
harvested in order to fulfill the demand
for mesquite charcoal, and former
mesquite forests have disappeared at an
alarming rate (Burquez and Martinez
Yrizar 2007, p. 545). Ironwood trees are
also being harvested in Mexico where
the wood is cherished for its hardness
and carving potential for native artwork
by groups such as the Seri Indians.
Mesquite and ironwood woodlands
provide pygmy-owl habitat elements
related to tree canopy cover and a
diverse prey base. Unfortunately,
woodcutters and charcoal makers do not
use scrubby-type mesquite, but rather
take advantage of large, mature mesquite
and ironwood trees growing in riparian
areas (Taylor 2006, p. 12), the exact tree
class that is of most value as pygmy-owl
habitat. From the time ‘‘mesquite
charcoal’’ became popular in U.S.
restaurants in the early 1980s, both
mesquite and ironwood have been
harvested from the same lands, with as
much as 15 to 40 percent of each
mesquite charcoal bag consisting of
ironwood prior to 1991. As a result,
both trees were locally overexploited in
Sonora and Baja California Sur (Taylor
2006, p. 12).
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Sonora supports 1,888,000 ha
(4,665,000 ac), or 46 percent of total
mesquite woodlands in Mexico; more
than double that of any other State in
Mexico. This also means that much of
the mesquite harvested in Mexico comes
from Sonora (Taylor 2006, p. 12).
Current estimates suggest that ironwood
is being rapidly depleted across an area
roughly equivalent to twice the size of
Massachusetts. In northern Mexico, over
202,000 ha (500,000 ac) of mesquite
have been cleared to meet the growing
demand for mesquite charcoal (Haller
1994, p. 1). Haller (1994, p. 3) predicted
that, if this trend continued, the entire
ecosystem of the Sonoran Desert could
crumble, and used the examples of the
degraded ecosystem along the coast of
Sonora near Kino Bay where most of the
mesquite and ironwood had already
been removed and virtually all plant
and animal life has disappeared.
Declining tree populations in the
Sonoran Desert as a result of
commercial uses and land conversion
threatens other plant species, and may
alter the structure and composition of
the vertebrate and invertebrate
communities as well (Bestelmeyer and
Schooley 1999, p. 644). This has
implications for pygmy-owl prey
availability because pygmy-owls rely on
a seasonal diversity of vertebrate and
invertebrate prey species; loss of tree
structure and diversity reduces prey
diversity and availability.
In the Sonoyta region of Sonora, an
area occupied by pygmy-owls, more
than 193,000 ha (478,000 ac) have been
affected by deforestation related to
charcoal production, brick foundries,
tourist crafts, and pasture conversion
(Nabhan and Suzan 1994, p. 64). The
accelerated rate of legume tree (trees
belonging to the family Leguminosae
whose characteristic fruit is a seed pod,
including the mesquite and ironwood)
depletion for charcoal and carvings in
the Mexican States of Sonora and Baja
California has clearly affected the health
of ironwood populations and associated
plant communities (Suzan et al. 1997, p.
955). This is evidenced by an increased
number of damaged and dying trees, as
well as generally small size classes for
sampled areas (Suzan et al. 1997, pp.
950–955).
Pressure for fuelwood and crafts
materials has been so intense in Mexico
south of Organ Pipe Cactus National
Monument that wood harvest,
especially ironwood, has been detected
more than 500 m (1600 ft) into the
Monument as supplies have been
depleted south of the border (Suzan et
al. 1999, p. 1499). The structure of both
wash and upland habitats in the
Monument have been affected by this
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harvest (Suzan et al. 1999, p. 1499).
Organ Pipe Cactus National Monument
is one of four areas in Arizona that has
been consistently occupied by pygmyowls. In the arid environment of the
Monument, tree canopy and structure
are particularly important pygmy-owl
habitat features.
Mesquite used as fuelwood is a
thriving cross-border trade, although not
on the same scale as charcoal. However,
local impacts can be significant in the
areas where the fuelwood is harvested.
For example, Mexican trucks loaded
with mesquite cross the border to
Arizona at Sasabe. Interviews with these
truck drivers indicated that most of the
wood they haul comes from ejidos
(communally owned lands) within a 20km (12.4-mi) radius of the Town of
Sasabe, an area occupied by nesting
pygmy-owls (Taylor 2006, p. 5; Flesch
2008, p. 2).
In 2008, during field work in Sonora
to gather pygmy-owl genetic samples,
large areas of charcoal production were
observed near Hermosillo. Impacts to
vegetation were not limited to just the
removal of the trees, but a significant
area around the production sites was
covered with fine, black charcoal dust
covering all native vegetation (Service
2009, p. 1). The effects of these
production areas are verified by reports
of the complete removal of a dense
mesquite bosque to the axe and charcoal
pits just east of Hermosillo (Taylor 2006,
p. 5). The immediate area around
charcoal pits is often treeless. Walking
transects away from charcoal pits
revealed that all trees within a 1-km
(0.6-mi) radius bear the scars of the
chainsaw (Taylor 2006, p. 7).
Native woodlands in Sonora are
additionally threatened as ranchers and
charcoal producers team up to first clear
the land of native trees for planting
buffelgrass, and then use the dead trees
to produce charcoal (Taylor 2006, pp. 6–
7). The end result is the incentive to
clear more native woodlands.
Professional woodcutters are only
permitted to harvest dead wood.
However, dead wood to meet export
demands is hard to come by. A simple
solution practiced by many wood
cutters is to ring trees and let them die;
then the dead wood can be legally
harvested (Taylor 2006, p. 7).
Impacts to pygmy-owl habitat in
northwestern Mexico from these
activities are resulting in the loss and
fragmentation of habitat in this part of
Mexico, and the inability to recover or
restore habitats and habitat connectivity
in Arizona. Impacts related to surfaceand groundwater loss and channel
diversions are long-term and are
particularly significant as riparian
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habitat, both meso- and xero-riparian,
are crucial for maintaining viable
pygmy-owl populations in the arid
portions of their range in Arizona and
Sonora, Mexico. Loss of leguminous
trees results in long-term effects to the
soil as they add organic matter, fix
nitrogen, and add sulfur and soluble
salts, affecting overall habitat quality
and quantity (Rodriguez Franco and
Aguirre 1996, p. 6–47). Ironwood and
mesquite trees are important nurse
species for saguaros, the primary nesting
substrate for pygmy-owls in the
northern portion of their range (Burquez
and Quintana 1994, p. 11). Demand for
mesquite charcoal and firewood
contributes to the loss of extensive,
mature mesquite forests in riparian
areas of northern Mexico.
The harvest of mature mesquites in
the Sonoran Desert for charcoal and
firewood permanently alters desert
ecosystems because leguminous trees
like mesquite and ironwoods are such
important anchors for these systems and
their associated flora and fauna (Taylor
2006, p. 8). Thus, ongoing wood
harvesting can reduce or eliminate
pygmy-owl habitat in the Sonoran
Desert region of Arizona and Mexico by
perpetuating scrubby trees that are
unsuitable for nest substrates,
supporting increased fire frequency
associated with nonnative grass
invasion, eliminating important nurse
trees for saguaro protection, reducing
tall canopy coverage important for
pygmy-owl cover, and altering prey
availability through the reduction of
structural diversity.
Once common in areas of the Rio
Grande delta, significant habitat loss
and fragmentation due to woodcutting
have now caused the pygmy-owl to be
a rare occurrence in this area of Texas.
Oberholser (1974, p. 452) concluded
that agricultural expansion and
subsequent loss of native woodland and
thornscrub habitat, begun in the 1920’s,
preceded the rapid demise of pygmyowl populations in the Lower Rio
Grande Valley of southern Texas.
Because much of the suitable pygmyowl habitat in Texas occurs on private
ranches, habitat areas are subject to
potential impacts that are associated
with ongoing ranch activities such as
grazing, herd management, fencing,
pasture improvements, construction of
cattle pens and waters, road
construction, and development of
hunting facilities. Brush clearing, in
particular, has been identified as a
potential factor in present and future
declines in the pygmy-owl population
in Texas (Oberholser 1974, p. 452).
However, relatively speaking, the
current loss of habitat is much reduced
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in comparison to the historic loss of
habitat in Texas. Conversely, ranch
practices that enhance or increase
pygmy-owl habitat to support
ecotourism can contribute to
conservation of the pygmy-owl in Texas
(Wauer et al. 1993, p. 1076). The best
available information does not indicate
that current ranching practices are
significantly affecting pygmy-owl
habitat in Texas.
Tamaulipan brushland is a unique
ecosystem that is found only in the
Lower Rio Grande Valley of south Texas
and northeastern Mexico. This
vegetation community has historically
supported occupancy by pygmy-owls.
Brush clearing, pesticide use, and
irrigation practices associated with
agriculture have had detrimental effects
on the Lower Rio Grande Valley
(Jahrsdoerfer and Leslie 1988, p. 1).
Since the 1920’s, more than 95 percent
of the original native brushland in the
Lower Rio Grande Valley has been
converted to agriculture or urban use.
Along the Rio Grande River below
Falcon Dam, 99 percent of the land has
been cleared for agriculture and
development. Cook et al. (2001, p. 3)
indicated that both banks of the Rio
Grande are now completely developed
with homes or farms, and that the only
remaining natural habitat areas south of
the river are salt marshes and mudflats,
both communities that are not used by
pygmy-owls. A large percentage of
similar habitat has been cleared in
Mexico (Jahrsdoerfer and Leslie 1988, p.
17). This is supported by Tewes’ (1992,
p. 29) conclusion that most of the Rio
Grande delta of Texas and Mexico has
been developed over the past 60 years.
Hunter (1988, p. 8) states, ‘‘Habitat
removal in Mexico is widespread and
nearly complete in northern
Tamaulipas.’’
Habitat fragmentation in northeastern
Mexico is extensive, with only about
two percent of the ecoregion remaining
intact, and no habitat blocks larger than
250 square km (96.5 square mi), and no
protected areas (Cook et al. 2001, p. 4).
This has the potential to limit pygmyowl movements and dispersal,
exacerbating the effects of small,
isolated populations. Fire is often used
to clear woodlands for agriculture in
this area of Mexico, and many of these
fires are not adequately controlled.
There may be fire-related effects to
native plant communities (Cook et al.
2001, p. 4); however, there is no
available information of how much area
may be affected by this activity.
The best available scientific and
commercial information indicates that
historical land clearing, as a result of
wood harvesting and agricultural
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development has caused the loss and
alteration of a considerable area of
pygmy-owl habitat in Arizona, Sonora,
Texas, and northeastern Mexico. Past
impacts continue to affect the extent of
available pygmy-owl habitat in these
areas, because of the extended time it
takes for these lands to recover, even if
negative actions cease, and impacts are
expected to continue in many of these
same areas into the foreseeable future.
However, based on our review of the
best available scientific and commercial
information, we conclude that these
impacts are limited in magnitude,
because they are significant only in the
northern portion of the range (Arizona,
Texas, northwestern and northeastern
Mexico). Moreover, the best available
scientific and commercial data indicate
that habitat loss due to woodcutting or
agriculture is primarily historical in
Texas, and these activities are not
currently impacting habitats occupied
by pygmy-owls on the private ranches
in Texas. Further, the impacts in the
southern portion of the range are less
extensive, both because woodcutting
and agricultural development appear to
have less impact in the southern portion
of the pygmy-owl’s range, and because
the pygmy-owl seems to be common
throughout this area. Therefore, after
reviewing and evaluating the best
available scientific and commercial
data, we conclude that woodcutting and
agricultural development are not threats
to the continued existence of the
pygmy-owl rangewide, and are not
likely to become so in the future.
Improper Livestock Grazing
Probably no single land use has had
a greater effect on the vegetation of
southeastern Arizona or has led to more
changes in the landscape than improper
livestock grazing and range-management
programs (Carothers 1977, p. 4).
Undoubtedly, grazing since the 1870s
has led to soil erosion, destruction of
those native plants most palatable to
livestock, changes in the regional fire
ecology, the spread of both native and
alien plants, and changes in the age
structure of evergreen woodlands and
riparian forests (Bahre 1991, p. 123).
Many areas of pygmy-owl habitat have
recovered from these historical effects of
grazing; however, other areas are slow to
recover and may never recover due to
the arid nature of the Sonoran Desert.
Livestock grazing in northwestern
Mexico is probably the most widespread
human use of Sonoran ecoregional
landscapes. Grazing by cattle, goats, and
other livestock has reduced vegetation
cover and helped change grasslands to
shrublands. Livestock grazing in the
Sonoran Desert has fluctuated greatly in
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the last few centuries from being
relatively confined and intensive to
being extensive and intensive. In the
19th century, repeated Apache raids on
ranchers and the paucity of water
limited cattle production to relatively
small areas (Bahre 1991, pp. 114–115).
However, the late 19th century saw the
largest stocking rates in history;
extensive cattle production played a
major role in the transformation of
grasslands to scrublands, down-cutting
of arroyos, the spread of nonnative
plants, and degradation of riparian
areas. Stocking rates are now much
lower than in the 1890s because
regulations such as those of the Taylor
Grazing Act of 1934 helped improve
rangeland quality in the United States.
However, overstocking still continues in
parts of northwestern Mexico, and
´
Mexico’s COTECOCA (Comision
´
Tecnico Consultiva de Coeficientes de
Agostadero) statistics confirm that 2 to
5 times the recommended stocking rates
occur with regularity on the Sonoran
side of the border (Walker and
Pavlakovich Kochi 2003, p. 14; Nabhan
and Holdsworth 1998, p. 2).
Available information on livestock
grazing in Mexico that we evaluated was
focused primarily on the border areas
adjacent to the United States and in the
arid areas of northwestern Mexico, such
as Sonora. In Sonora, rangelands are
often heavily grazed, with effects
particularly apparent during drought
(Rorabaugh 2008, p. 25). Sonora’s higher
stocking rate is likely due to its greater
amounts of private and ejidal
(communal) land, less regulation, and
the greater dependence on ranching and
farming in Mexico. Demand in North
America drives the number of cattle in
Sonora. The number of cattle in Sonora
nearly doubled between 1950 and 1960.
The Sonoran cattle population was
1,652,771 in 1990 according to official
government statistics (Hawks 2003, p.
5). Other authors estimate the
overstocking at 177 percent (Lopez
1992), with 60 to 400 percent
overstocking in some areas (BurquezMontijo et al. 2002, p. 134). Excessive
grazing of vegetation by livestock,
especially when combined with
conversion of plant cover to exotic
pasture grasses, ranked as number four
on a list of threats to the Sonoran Desert
Ecoregion (Nabhan and Holdsworth
1998, p. 1).
One research study showed that
overgrazing in Sonora leaves the
Mexican landscape more exposed and,
as a result, it dries out more rapidly
following summer convective
precipitation. After about 3 days,
depletion of soil moisture evokes a
period of higher surface and air
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temperatures in northwestern Mexico
(Bryant et al. 1990, pp. 254–258). These
drier soils and higher temperatures can
result in impacts to vegetation survival
and persistence. Effects of poorly
managed livestock grazing in Sonora
include changes in plant species
composition and vegetation cover and
structure, soil compaction, erosion,
altered fire regimes, and nonnative plant
species introductions and invasions
(Stoleson et al. 2005, pp. 61–62). With
regard to pygmy-owl habitat, improper
stocking rates can result in reduced
saguaro reproduction through trampling
and alteration of microclimates
(Abouhaider 1989, pp. 40–48), reduced
tree cover and reproduction through
grazing of seedlings and seed pods, and
impacts to prey availability from
reduced vegetation structural diversity
and species composition.
One of the most significant adverse
impacts within western riparian systems
has been the perpetuation of improper
grazing practices. Belsky et al. (1999, p.
419) found that grazing by livestock has
damaged 80 percent of the streams and
riparian ecosystems in the arid regions
of the western United States. The initial
deterioration of western riparian
systems began with the severe
overgrazing in the late nineteenth
century. Livestock grazing can affect
four general components of riparian
systems: (1) Streamside vegetation; (2)
stream channel morphology; (3) shape
and quality of the water column; and (4)
structure of streambank soil. Vegetation
impacts include: (1) Compaction of soil,
which increases runoff and decreases
water availability to plants; (2) herbage
removal, which allows soil temperatures
to rise, thereby increasing evaporation;
(3) physical damage to vegetation by
rubbing, trampling, and browsing; and
(4) alteration of growth form of plants by
removing terminal buds and stimulating
lateral branching (Fleischner 1994, p.
635).
In a summary of studies investigating
the impacts of livestock grazing on
riparian areas, Belsky et al. (1999, p.
425) found that none of the studies
showed positive impacts or ecological
benefits that could be attributed to
livestock activities when grazed areas
were compared to protected areas. It
was mostly negative effects that were
reported, and there was little debate
about those effects. Most of these
studies tended to agree that improper
livestock grazing can damage stream
and riparian ecosystems. All types of
riparian habitats provide important
pygmy-owl habitat elements due to the
increased size, diversity, and structure
associated with riparian communities
and enhanced moisture availability.
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Larger trees provide substrates for nest
cavities. Structure diversity provides
important predator and
thermoregulatory cover, as well as an
increased number and diversity of prey
species. A reduction of the extent or
quality of riparian habitats within the
range of the pygmy-owl represents
direct impacts on the availability and
quality of pygmy-owl habitat.
Although proper management has
greatly improved riparian communities
in some areas, field data compiled in the
last decade showed that riparian areas
throughout much of the West were in
the worst condition in history due
mainly to the complications initiated by
improper grazing techniques (Krueper
1993, p. 322). However, information
submitted during the public comment
period supports the idea that, in certain
areas, riparian habitat has returned and,
perhaps, even increased in certain areas
in Arizona, including areas that are
being grazed by livestock. Parker (2008,
p. 13) points out that Webb et al. (2007,
pp. 388–389, 404–408) conclude that, in
the drainages they studied, increases in
riparian vegetation from 24 percent to
49 percent had occurred since the late
1800s and early 1900s, and that
increases in the density of riparian
plants appear to have accelerated in the
1970s. We are encouraged by this
positive information indicating that
riparian habitats in some areas may
become suitable for pygmy-owls in the
future if grazing continues to be
properly managed. It is not our
contention that grazing per se has a
negative effect on riparian areas, but
that improper or overgrazing can have
detrimental effects. Parker (2008, p. 14)
reiterates this by stating, ‘‘While there is
little question that overgrazing can
degrade riparian ecosystems, the
question here is whether grazing has
had long-term negative effects on woody
riparian vegetation in Arizona.’’ We
acknowledge that, with proper
management, riparian areas can recover
and provide habitat for the pygmy-owl.
In Mexico, increasing human
population numbers and the extent of
subsistence agriculture threatens the
future of Mexico’s extensive riparian
systems. Grazing impacts include
contamination and an increasing
demand for agricultural and forage
production (Deloya 1985, pp. 9–11).
Riparian destruction is evident
throughout Mexico, but especially in
areas of denser human population. Of
particular relevance to the pygmy-owl
has been the loss and destruction of
virtually all of the dense woodlands
within the Rio Grande River valley.
Despite the evident destruction of
riparian systems, little information
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exists on the problem and there is
apparently no strategy at a national level
to solve the problem. The present trends
pose serious concerns for the future of
Mexico’s riparian ecosystems (Deloya
1985, pp. 11–12).
In Texas, areas occupied by pygmyowls are primarily on large, private
ranches where livestock production is a
primary objective. However, alternative
sources of revenue for these ranches
also include hunting and ecotourism. As
a result, habitat management for the
benefit of wildlife is also a high priority
for these ranchers. Livestock
management is often conducted with
consideration of impacts to wildlife.
Pygmy-owls are known to exist in
areas that are grazed. Grazing, itself,
does not appear to negatively affect
pygmy-owls. Properly managed grazing
can enhance certain pygmy-owl habitat
elements (Loeser et al. 2007, p. 96;
Holechek et al. 1982, p. 208). Climatic
variation is important in determining
the ecological effects of grazing
practices in arid rangelands (Loeser et
al. 2007, pp. 93–96). However, improper
grazing at inappropriate stocking rates
or during seasons or years when drought
and other conditions reduce forage
availability can affect pygmy-owls
directly through the loss of important
habitat elements (e.g., saguaros, tree
cover, riparian vegetation, vegetation
reproduction) and prey availability. No
studies specifically related to the effects
of livestock grazing on pygmy-owls have
been conducted; however, impacts to
pygmy-owls can be determined
indirectly from studies on related
species or issues. For example, studies
in Arizona and Sonora show that the
number of lizard species and abundance
of lizards declined significantly in
heavily grazed areas (Jones 1981, p.
111); there is also a likely loss of lizard
species in areas invaded by buffelgrass.
Lizards are an important food resource
for pygmy-owls; therefore, impacts to
lizard abundance can affect pygmyowls.
An additional concern related to
grazing lands is that, faced with rising
land prices, unstable markets, and
unpredictable climate, many ranchers in
the United States are choosing or are
forced to sell their private lands to real
estate developers or subdivide it
themselves. This results in these lands
being subject to the threats described
above related to urbanization. There was
no available information to determine if
these same pressures apply to grazing
lands in Mexico.
Improper livestock grazing has a
negative impact on pygmy-owl habitat
under some circumstances in Arizona
and Sonora. While we expect that
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continued implementation of improved
grazing-management techniques will
reduce grazing impacts on pygmy-owls
in Arizona and Texas, we expected that
overgrazing will continue to negatively
impact pygmy-owls in Sonora and other
parts of northern Mexico. Within the
Sonoran desert, over grazing can result
in loss of structural habitat components
important to pygmy-owls, as well as
reducing prey availability and diversity.
Additionally, improper grazing during
droughts can affect the long-term
viability of riparian habitats, which are
an important habitat type for pygmyowls in Arizona and Sonora. However,
there is no indication that livestock
grazing precludes occupancy by pygmyowls in any part of its range. While
improper livestock grazing can have
negative impacts to local pygmy-owl
populations, we do not believe livestock
grazing is significantly affecting pygmyowl populations throughout its range.
The best available scientific and
commercial information does not appear
to indicate that improper grazing is
affecting pygmy-owl populations in
Texas. We have no readily-available
information to determine whether the
effects of livestock grazing on pygmyowl habitat in Mexico outside of Sonora
are greater or more harmful than in
Arizona and Sonora, but we suspect
impacts are similar. Based on the best
available scientific and commercial
data, we conclude that improper
livestock grazing is not a threat to the
continued existence of the pygmy-owl
rangewide, nor is it likely to become so.
Border Issues
One of the most pressing issues for
the Arizona-Sonora border is the impact
of illegal human and vehicular traffic
through these unique and
environmentally sensitive areas. Many
of these locations now bear the scars of
wildcat trails, abandoned refuse, and
trampled vegetation (Marris 2006, p.
339; Walker and Pavlakovich-Kochi
2003, p. 15). Monitoring activities by the
U.S. National Park Service (NPS)
estimate that, annually, 300,000
individuals illegally cross through
Organ Pipe Cactus National Monument
in southwestern Arizona. Video
surveillance equipment erected at
Coronado National Memorial, in
southeastern Arizona, indicates traffic
volumes ranging from 100 to 150
immigrants per night (Walker and
Pavlakovich-Kochi 2003, p. 15). In the
Cabeza Prieta National Wildlife Refuge,
located in southwestern Arizona, which
supports resident pygmy-owls, there are
over 640 km (400 mi) of illegal roads
plus another 1,280 km (800 mi) of
unauthorized foot trails as a result of
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illegal border activities (Cohn 2007, p.
96). These activities result in direct
impacts to pygmy-owl habitat.
Additional information from the NPS
indicates a significant issue ‘‘* * * is
the increasing drug smuggling, illegal
immigrants, and law enforcement
activity which results in much greater
human disturbance of the birds.’’
Further elaboration shows that the NPS
believes ‘‘* * * that cactus ferruginous
pygmy-owls within the Monument have
been subject to repeated disturbance
events and some habitat degraded as a
result of long-term drought and impacts
associated with illegal migration, drug
smuggling, and law enforcement
interdiction efforts’’ (Snyder 2005, pp.
1–3). Trails and roadways remove
pygmy-owl habitat features, noise and
disturbance from people and vehicles
disrupt important behaviors, and there
is an increased risk of fire in important
habitats resulting from cooking and
warming fires, as well as signal fires
used by cross-border immigrants and
smugglers. Areas occupied by pygmyowls in Organ Pipe Cactus National
Monument have been abandoned by the
owls, likely due, at least in part, to
heavy illegal immigrant traffic and
associated enforcement actions.
There is fear that efforts to curb illegal
border activities through the
construction of infrastructure such as
fences and barrier will fragment the
Sonoran Desert ecosystem, damage the
desert’s plant and animal communities,
and prevent free movement of wildlife
between the United States and Mexico
(Cohn 2007, p. 96). During the time the
pygmy-owl was listed under the Act, we
consulted on the effects of Federal
border infrastructure projects and
identified a number of potential impacts
(Service 2003, pp. 66–85). The
construction of new border
infrastructure in the form of pedestrian
fences, vehicle barriers, and patrol roads
create impediments to pygmy-owl
movement across the border due to
pygmy-owl flight patterns and behavior
(Marris 2006, p. 239; Vacariu 2005, p.
354). The fences and vehicle barriers,
when considered in conjunction with
patrol roads, drag roads, and vegetation
removal, result in a combination of
nonvegetated area with a raised
structure in the middle causing an
impediment to pygmy-owl movement,
particularly given their normal flight
patterns, where normal flights are
generally less than 30 m (100 ft) and
typically only 1.5 to 3.0 m (5 to 11 ft)
above the ground (Flesch and Steidl
2007, p. 35; AGFD 2008b, p. 5). Flesch
et al. (2009, pp. 7–9) show that the
vegetation gaps, in association with the
tall fences, may limit transboundary
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movements by pygmy-owls. Raptors are
often attracted to artificial hunting
perches, especially in areas that lack tall
trees (Oles 2007, p. 1; Heintzelman
2004, p. 35; Askham 1990, p. 147).
Border fences can provide open hunting
areas and improved hunting perches for
a variety of raptors that are potential
predators of pygmy-owls. This
combination of perches, open area, and
an impediment to movement may result
in increased predation of pygmy-owls,
particularly dispersing juvenile pygmyowls. Because the overall population of
pygmy-owls likely functions as a
metapopulation, the pygmy-owl
depends on dispersal, emigration, and
immigration to maintain the genetic and
demographic fitness of regional
populations. To the extent that border
infrastructure and activities reduce or
prevent such movements, and increase
the likelihood of pygmy-owl predation,
it follows that population-level impacts
may result.
Impacts to pygmy-owls from border
infrastructure and illegal activities are
likely limited to the immediate border
areas of Arizona and northern Sonora.
Information was not readily available so
that we could determine the extent of
these impacts in Texas and northeastern
Mexico, although they are likely to be
similar (habitat gaps, perches for
raptors, etc.). Nevertheless, these
impacts are restricted to the border
regions of Arizona and Texas, and only
affect a relatively-small portion of the
pygmy-owl range. This localized effect
reduces the magnitude of this impact to
the overall pygmy-owl population.
Therefore, based on the best available
scientific and commercial data, we
conclude that effects associated with
border activities are not a threat to the
continued existence of the pygmy-owl
rangewide, and are not likely to become
so in the future.
Off-Highway Vehicle (OHV) Use
The information we have on impacts
to the pygmy-owl from OHV use relates
primarily to Arizona. Information was
not readily available on any potential
OHV impacts to pygmy-owls or pygmyowl habitat in Texas and Mexico.
OHV use is widespread in Arizona
and occurs on lands under a variety of
management entities including the
Forest Service, Bureau of Land
Management, State Land Department,
Tribes, and private individuals. The use
of OHVs has grown considerably. For
example, as of 2007, 385,000 OHVs
were registered in Arizona (a 350
percent increase since 1998) and 1.7
million people (29 percent of Arizona’s
population) engaged in off-road activity
from 2005 to 2007 (Sacco 2007). Over
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half of OHV users reported that merely
driving off the paved road was their
primary activity, versus using the OHV
for the purpose of seeking a destination
to hunt, fish, or hike (Sacco 2007).
Specific impacts to the pygmy-owl or its
habitat from OHV use when driving off
road include disturbance from noise and
human activity, vegetation damage,
changes in plant abundance and species
composition, reduced habitat
connectivity, soil compaction, soil
erosion, reduced water infiltration,
higher soil temperatures, destruction of
cryptogamic soils (soil with crusts
formed by an association of algae,
mosses, and fungi; such crusts stabilize
desert soil, retain moisture, and protect
germinating seeds), and increased firestarts (Boarman 2002, pp. 46–47; Ouren
et al. 2007, pp. 6–7, 11, 16).
Of specific concern is the regular use
by OHV operators to utilize xeroriparian washes as travel ways. These
washes provide important habitat
elements for pygmy-owls due to the
increased structure and productivity of
vegetation resulting from the presence
of increased moisture. Pygmy-owls use
these wash areas for foraging, dispersal,
thermal and predator cover, and for
movements within their home range.
Wash areas are often narrow and
constrained, resulting in OHV impacts
to vegetation and concentrated noise
and disturbance, affecting the use and
suitability of these areas as pygmy-owl
habitat.
Pygmy-owls may be affected by OHV
use in riparian areas. However, this
effect is temporary and not continuous.
Pygmy-owls may leave the area if
disturbed by noise and return once the
activity has ceased. Pygmy-owl habitat
destruction in Arizona may result from
OHV activity, but the magnitude and
severity of this impact is relatively
minor. Based on our evaluation of the
best available scientific and commercial
data, we conclude that OHV use does
not threaten the continued existence of
pygmy-owl, and is not likely to do so in
the future.
Summary of Factor A
In summary, pygmy-owls require
habitat elements such as mature
woodlands that include appropriate
cavities for nest sites, adequate
structural diversity and cover, and a
diverse prey base. A number of negative
impacts described in Factor A are
affecting pygmy-owl habitat within
portions of its range. However, the best
available scientific and commercial
information indicates that most of these
impacts are either restricted to or are
greater in a smaller subset of the pygmyowl’s range (approximately 27 percent).
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For instance, we have detailed
information that in the Arizona and
Sonoran Desert Ecoregion, pygmy-owl
habitat loss and fragmentation resulting
from urbanization, changing fire regimes
due to the invasion of buffelgrass,
agricultural development and
woodcutting, overgrazing, and border
issues have had significant negative
impacts on pygmy-owl habitat in these
areas and will likely continue to do so
to varying degrees in the foreseeable
future. In Texas, which comprises
approximately five percent of the
pygmy-owl’s range, historical loss of
habitat has reduced the pygmy-owl
range, but current impacts, such as
livestock grazing and the invasion of
nonnative plants, are reduced in their
magnitude and severity.
For the larger part of the pygmy-owl’s
ranger in Mexico (the remaining 73
percent south of Sonora), the best
available data indicates that many
impacts to pygmy-owl habitat are
reduced in their magnitude and severity
or absent altogether. The rate of growth
in these southern Mexican States is
relatively slow compared with growth
in Sonora and the Arizona border region
and is expected to remain that way.
Agricultural development has decreased
in these areas, and buffelgrass is not a
known threat to pygmy-owl habitat in
this area and is not expected to become
a threat in the future because of
unfavorable growth conditions for
buffelgrass. Historical loss of pygmy-owl
habitat in northeastern Mexico has
occurred, but there is no available
evidence that significant habitat
destruction is currently taking place. In
addition, pygmy-owls are still
considered common in the southern
portion of their range. This information
indicates that the negative impacts to
pygmy-owl habitat discussed herein
have different levels of effects on the
populations of pygmy-owls throughout
their range, and are much reduced or
absent in the southern portion of the
pygmy-owl’s range. Based on the best
available scientific and commercial
information, we conclude that the
present or threatened destruction,
modification, or curtailment of its
habitat or range is not a threat to the
pygmy-owl rangewide now or in the
foreseeable future.
Factor B: Overutilization for
Commercial, Recreational, Scientific, or
Educational Purposes
We are unaware of any overutilization
of pygmy-owls for commercial,
scientific, or educational purposes.
However, the pygmy-owl is highly
sought after by birders, who concentrate
at several of the remaining known
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locations of pygmy-owls in the United
States. For example, in 1996, a resident
in Tucson reported a pygmy-owl
sighting (documented pair) that
subsequently was added to a local
birding hotline, and the location was
added to their website on the internet.
Several carloads of birders were later
observed in the area of the reported
location (AGFD 1999, p. 12). As recently
as 2003, property owners in Tucson
have expressed concerns that birders
and others have been documented
trying to get photos or see pygmy-owls
at occupied sites (AGFD 2003, p. 1).
In Texas, Tewes (1992, p. 28) states,
‘‘Frequent disruption by wellintentioned bird enthusiasts with call
imitations may produce a local risk to
the pygmy-owls, especially during
breeding season.’’ We believe this
disturbance problem is most significant
in southern Texas. Oberholser (1974, p.
452) made a similar observation: ‘‘They
[pygmy-owls] are considerably
disturbed by hordes of bird watchers,
some of whom keep their portable tape
recorders hot for hours at a time in
hopes that one of these rare birds will
answer.’’ Recreational disturbance of
pygmy-owls in Texas is particularly an
issue in the side patches of mesquite,
ebony, and cane in Starr and Hidalgo
Counties (Oberholser 1974, p. 452).
Oberholser (1974, p. 452) and Hunter
(1988, p. 6) suggest that recreational
birding may disturb pygmy-owls in
highly visited areas, affecting their
occurrence, behavior, and reproduction.
Tewes (1992, p. 12) indicates that many
amateur and professional ornithologists
have strictly controlled or eliminated
their use of taped calls to locate pygmyowls because of the potential to affect
the pygmy-owl’s behavior.
Currently, a number of ranches in
Texas offer the opportunity to view and
photograph pygmy-owls. An internet
search revealed invitations to birders to
view pygmy-owls on the Canelo, King,
and San Miguelito ranches.
Additionally, both the AGFD and the
Service continue to get requests to view
and photograph pygmy-owls in Arizona.
Summary of Factor B
In summary, impacts to pygmy-owls
from over-zealous birdwatchers have
been documented in some areas within
the range of the pygmy-owl. While
pygmy-owls continue to be a highly
sought after species by birders, there is
some indication that compliance with
etiquette related to use of tape-playback
or call imitation has improved. We were
unable to find any information on the
effects of birding on pygmy-owls in
Mexico, but we do not believe that it is
a significant issue in Mexico, except
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perhaps on local ranches or ejidos
where ecotourism and bird watching are
promoted. While the above impacts may
negatively affect individual pygmy-owls
on a local basis, landowners in areas
that promote ecotourism are also likely
to implement actions that have positive
effects for the pygmy-owl. We conclude,
based upon our review of the best
commercial and scientific data
available, that overutilization for
commercial, recreational, scientific, or
educational purposes is not a threat to
the pygmy-owl now or likely to become
so.
Factor C: Disease or Predation
Documentation of disease or
predation as a significant mortality
factor within a wildlife population
requires extensive monitoring and the
ability to observe individuals in hand.
With regard to pygmy-owls, monitoring
and capture has only occurred with any
regularity in Arizona and Texas within
the United States. This has included the
capture of hundreds of individual
pygmy-owls and subsequent monitoring
using radio telemetry. Consequently, all
of the available information on disease
and predation is from Arizona and
Texas. We are aware of only limited,
anecdotal information related to
predation for northwestern Mexico
(Flesch 2010, pers. comm.). The
following discussion outlines our
evaluation of the information related to
disease and predation that we have
available from Arizona and Texas.
Little is known about the rate or
causes of mortality in pygmy-owls;
however, they are susceptible to
predation from a wide variety of
species. Recent research indicates that
natural predation likely plays a key role
in pygmy-owl population dynamics,
particularly after fledging and during
the postbreeding season (AGFD 2003, p.
2). AGFD telemetry monitoring in 2002
indicated at least three of the nine
young produced that year were killed by
predators prior to dispersal during a
year when tree species failed to leaf out
due to drought conditions (AGFD 2003,
p. 2). Increased predation during a
particularly harsh drought year (2004)
in Arizona prompted a rescue effort by
the AGFD and the Service during which
two hatch-year pygmy-owls were
temporarily brought into captivity to
increase their chances of survival. They
were subsequently released when
habitat conditions improved (Service
2004, p. 1). Pygmy-owl predation by
screech owls has been identified as a
potential factor contributing to the
decline of regional pygmy-owl
population groups (AGFD 2008b, p. 9).
However, there is not enough
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information to conclusively support this
hypothesis. Predation is a significant
pygmy-owl nest mortality factor
associated with nest boxes and tree
cavities in Texas. Proudfoot (2011a, p.
1) indicates that predation rates on
natural cavities and unprotected nest
boxes have been as high as 40 to 60
percent, with an average of 25 to 30
percent.
Domestic cat predation of pygmy-owls
has been documented in both Texas and
Arizona (AGFD 2003, p. 1; Proudfoot
1996, p. 79). Human population growth
can increase the numbers of subsidized
predators, such as household cats, that
can affect pygmy-owl populations. As
the number of potential predators
increases, the chance of predation on
pygmy-owls increases. In addition,
domestic house cats consume
considerable quantities of birds,
reptiles, insects, and small mammals,
reducing available pygmy-owl prey
availability (Barratt 1995, p. 185;
Coleman et al. 1997, p. 2; Evans 1995,
p. 4). This introduction of additional
potential predators and a reduction in
prey availability negatively affects
pygmy-owls.
Ectoparasites have recently been
identified as a potential threat to
pygmy-owl populations (Proudfoot et al.
2005, pp. 186–187; Proudfoot et al.
2006c, pp. 874–875). These recent
investigations in Texas and Arizona
have indicated the regular occurrence of
avian parasites in the materials inside of
pygmy-owl nest cavities. The numbers
of parasites may be high enough to
affect nestling pygmy-owl health and
survival. Blood parasites have been
implicated in reduced body condition
and impacts to survival and dispersal in
small raptors (Dawson and Bortolotti
2000, pp. 3–5). Proudfoot et al. (2005,
pp. 186–187) could not rule out that
blood loss from external parasites, in
combination with other factors, may
have contributed to the loss of an entire
clutch of pygmy-owls in Arizona.
The West Nile virus has been
identified as the cause of a number of
raptor mortalities throughout the United
States, including Arizona. A number of
North American owl species have
documented mortality from West Nile
virus, including the northern pygmyowl (Gancz et al. 2004, p. 2139).
However, the West Nile virus has not
been documented in cactus ferruginous
pygmy-owls in either the United States
or Mexico, and no pygmy-owl
mortalities have been suspected to be
the result of an infection with the West
Nile virus.
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Summary of Factor C
In summary, our review of the best
available information suggests that
disease and predation clearly have the
potential to affect pygmy-owl
individuals and populations, and have
done so in local populations. However,
information related to these factors is
limited to pygmy-owl populations in the
United States. We have only limited,
anecdotal information related to
predation on pygmy-owls in Mexico.
Even in the United States, where
predation has been documented, we
conclude that it is not resulting in
significant effects to the status of the
pygmy-owl, because no disease or
predation effects have been identified as
having population-level effects on
pygmy-owls. Based upon our review of
the best commercial and scientific data
available, we conclude that disease and
predation are not threats to the pygmyowl now or in the future.
Factor D: Inadequacy of Existing
Regulatory Mechanisms
Regulations that could potentially
address conservation of the pygmy-owl
or pygmy-owl habitat in both the United
States and Mexico may occur at a
number of different levels of
government, from Federal to local. The
following discussion addresses the
existing regulatory mechanisms related
to the conservation of pygmy-owls and
pygmy-owl habitat based on the best
available information.
Although the pygmy-owl in Arizona
is considered nonmigratory, it is
protected under the Migratory Bird
Treaty Act (MBTA) (16 U.S.C. 703–712).
The MBTA prohibits ‘‘take’’ of any
migratory bird; however, unlike take
under the Endangered Species Act,
some Federal courts have concluded
that the MBTA does not apply to
indirect forms of take such as habitat
destruction, unless direct mortality or
destruction of an active nest occurs
during the activity that causes the
habitat destruction. Other Federal and
State regulations and policies, such as
the Clean Water Act, the Department of
Defense’s Integrated Natural Resources
Management Plans (Barry M. Goldwater
Range) (Uken 2008, p.1), National Park
Service policy, the inclusion of the
pygmy-owl on the State of Arizona’s list
of Species of Special Concern (AGFD
1996, p. 15), and various municipal
planning documents (Oro Valley 2008,
p. 1) provide varying levels of
protection, but have not been effective
in protecting the pygmy-owl in Arizona
from further decline. As a result of the
implementation of the 2005 Real ID Act,
the U.S. Department of Homeland
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Security has waived application of the
Endangered Species Act and other
environmental laws in the construction
of border infrastructure, including areas
occupied by the pygmy-owl (73 FR
5271). Some local conservation
mechanisms, such as habitat
conservation plans, are in development
in southern Arizona. These plans
include conservation measures for
pygmy-owls, but are at least a year from
completion, and as drafts, do not afford
the pygmy-owl any level of protection
or conservation (although some pygmyowl habitat has been conserved through
acquisitions related to these plans).
There are currently no statutory or
regulatory provisions under Arizona law
addressing the destruction or alteration
of pygmy-owl habitat.
One member of the public provided
information indicating that, because the
current distribution of pygmy-owls
occurs primarily on lands under
Federal, State, or Tribal control, these
lands are not at risk for the primary
threats that have been identified (James
2008, p. 8). However, activities occur on
all these lands that can result in all of
the negative impacts to pygmy-owls
identified in our 90-day finding and this
document. None of these types of lands
are immune to or restricted from
impacts of facilities development,
nonnative invasive species, changing
fire regimes, drought, climate change,
wood harvesting, bird watching, avian
disease and predation, border issues, or
any of the other impacts discussed
above. In fact, it is on these very lands
that many of these impacts, such as
border issues, nonnative species
invasions, fire, and recreation are
concentrated. As discussed above,
existing regulations governing these
lands do not specifically protect pygmyowls or their habitats, particularly
absent protection under the Act.
A potential regulatory effect not
specifically related to protection of the
pygmy-owl, but which will affect our
ability to conserve the pygmy-owl, has
recently come to light with regard to
Arizona State Trust lands. The Arizona
State Land Department is considering
restricting access to State Trust Lands
for the purposes of conducting wildlife
studies. Such access restrictions might
prohibit further surveys, research, and
monitoring of pygmy-owls on State
Trust lands, due to new permit
requirements and substantial cost. This
has not been formally adopted and may
be changed prior to finalization (Latimer
2010, p. 1). However, if implemented as
described by Latimer (2010, p. 1), these
proposed procedures and fees would
likely limit pygmy-owl research on State
Trust lands because of our and other
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biologists’ inability to meet the
requirements or pay the fees. This
would have a substantial negative effect
on our ability to conserve pygmy-owls
within Arizona.
The State of Texas lists the pygmyowl as threatened (TPWD 2009, p. 1).
This designation requires permits for
take of individuals for propagation,
zoological gardens, aquariums,
rehabilitation purposes, and scientific
purposes (Texas Parks and Wildlife
Code Chapters 67 and 68; Texas
Administrative Code Sections 65.171–
65.176, Title 31). There are no
provisions for habitat protection. The
pygmy-owl is also on the Texas
Organization for Endangered Species
(TOES) ‘‘watch list,’’ but this list
provides no regulatory protection for the
species or its habitat (TOES 1995, p. 1).
The establishment of protected areas
of habitat and management to enhance
or restore habitat are important to the
conservation of pygmy-owl populations
in both the United States and Mexico.
In the United States, this could
potentially be accomplished on lands
managed by Federal agencies such as
the Park Service, Bureau of Land
Management, Department of Defense,
and the Service. However, many of
these lands have a multiple-use
mandate and do not focus solely on
pygmy-owl conservation, or even
wildlife conservation in general. Similar
issues exist in Mexico as well. Goals
and objectives of wildlife management
in Mexico have primarily focused on
huntable or harvestable species.
A Mexican program to protect
sensitive habitats and species is the
National Natural Protected Areas
(NPAs) system. NPA designation is
supposed to protect areas that have not
been significantly altered by human
activities and that provide diverse
ecosystem services. However, prior to
1994, most NPAs lacked sound and
comprehensive management plans. By
2000, approximately 30 percent of new
and existing NPAs had developed
management plans. However, under the
NPA model, these plans lacked detailed
information, and in many cases could be
considered obsolete. NPA goals to
promote sustainable natural resources
were often unattainable because of
conflicting land ownership interests
(Valdez et al. 2006, p. 272). The
allocation of funds for management of
natural reserve areas in Sonora is
precarious, and some reserves have not
received protection other than that
given by government edicts or their
natural isolation (Burquez and
Martinez-Yrizar 1997, p. 378). Urban
development has taken its toll on
Sonora’s natural reserves. Three of the
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reserves have already disappeared,
which reflects the tenuous state of many
nature reserves in Mexico during the
1990s (Burquez and Martinez-Yrizar
2007, p. 546).
Another program set up to promote
wildlife management on private
property in Mexico is the development
of wildlife management units, or UMAs.
The UMA program in Mexico has not
been effective in promoting wildlife
management or biodiversity
conservation. It has increased the
introduction of exotic wildlife species to
meet hunting demands. There is a lack
of technical capability on private lands
to conduct proper wildlife monitoring
and management (Weber et al. 2006, p.
1482). In Mexico, the exploitation of
minerals and industrial development
has not been matched by strong
measures to protect the environment
(Burquez and Martinez-Yrizar 2007, p.
547). Riparian management in particular
seems to lack sufficient efforts (Kusler
1985, p. 6).
Summary of Factor D
In summary, Federal laws such as the
Migratory Bird Treaty Act and Arizona
and Texas State laws do address direct
take of pygmy-owls within the United
States. Existing regulations in Mexico
do not protect or conserve pygmy-owls.
Laws and regulations within the range
of the pygmy-owl in both the United
States and Mexico do not address the
loss of or impacts to pygmy-owl habitat.
However, within the majority of the
range of the pygmy-owl, the inadequacy
of existing regulations does not appear
to affect the frequency or magnitude of
impacts to pygmy-owls and their
habitat. Therefore, based on the best
scientific and commercial information
available, we find that, despite the lack
of specific laws or regulations
addressing impacts to and conservation
and protection of pygmy-owls and their
habitat, the inadequacy of regulatory
mechanisms does not threaten the
pygmy-owl rangewide, and is not likely
to do so in the future.
Factor E: Other Natural or Man-Made
Factors Affecting Its Continued
Existence
We briefly discussed the effects of
introduced predation on pygmy-owls by
domestic house cats in our Factor C
analysis above. While this is a manmade
factor affecting pygmy-owls, for Factor E
we will discuss human-caused mortality
that is not associated with any of the
other factors, for example, collisions
with fences, cars, and windows, and
shooting. Natural factors affecting
pygmy-owl habitat availability and
suitability not related to Factor A will
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also be discussed under Factor E. These
include drought, climate change,
hurricanes, and the effects of small
populations.
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Human-Caused Mortality
Direct and indirect human-caused
mortalities (e.g., collisions with cars,
glass windows, fences, power lines,
introduced competitors and predators,
etc.), while likely uncommon, are often
underestimated, and probably increase
as human interactions with pygmy-owls
increase (Banks 1979, pp. 13–14; Klem
1979, pp. 1–2; Churcher and Lawton
1987, p. 439). This may be particularly
important in areas of the pygmy-owl’s
range where pygmy-owls are located in
proximity to urban development.
Documentation exists of pygmy-owls
flying into windows and fences,
resulting in serious injuries or death to
the birds. In one incident, a pygmy-owl
collided with a closed window of a
parked vehicle; it eventually flew off,
but had a dilated pupil in one eye,
indicating neurological injury as a result
of this encounter (Abbate et al. 1999, p.
58). In another incident, an adult
pygmy-owl was found dead at a wire
fence; apparently it flew into the fence
and died (Abbate et al. 2000, p. 18).
AGFD also has documented an incident
of individuals shooting BB guns at birds
perched on a saguaro that contained an
active pygmy-owl nest. The information
we have related to human-caused
mortality is limited to the United States
and does not generally appear to be a
significant effect on pygmy-owl
populations. Information from Mexico
does not indicate that these activities
are affecting pygmy-owls in a manner
different than the United States.
Drought and Climate Change
‘‘Climate’’ refers to an area’s long-term
average weather statistics (typically for
at least 20- or 30- year periods),
including the mean and variation of
surface variables such as temperature,
precipitation, and wind, whereas
‘‘climate change’’ refers to a change in
the mean and/or variability of climate
properties that persists for an extended
period (typically decades or longer),
whether due to natural processes or
human activity (Intergovernmental
Panel on Climate Change (IPCC) 2007a,
p. 78). Although changes in climate
occur continuously over geological time,
changes are now occurring at an
accelerated rate. For example, at
continental, regional and ocean basin
scales, recent observed changes in longterm trends include: a substantial
increase in precipitation in eastern parts
of North American and South America,
northern Europe, and northern and
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central Asia, and an increase in intense
tropical cyclone activity in the North
Atlantic since about 1970 (IPCC 2007a,
p. 30); and an increase in annual
average temperature of more than 2° F
(1.1°C) across US since 1960 (Global
Climate Change Impacts in the United
States (GCCIUS) 2009, p. 27). Examples
of observed changes in the physical
environment include: An increase in
global average sea level, and declines in
mountain glaciers and average snow
cover in both the northern and southern
hemispheres (IPCC 2007a, p. 30);
substantial and accelerating reductions
in Arctic sea-ice (e.g., Comiso et al.
2008, p. 1), and a variety of changes in
ecosystem processes, the distribution of
species, and the timing of seasonal
events (e.g., GCCIUS 2009, pp. 79–88).
The IPCC used Atmosphere-Ocean
General Circulation Models and various
greenhouse gas emissions scenarios to
make projections of climate change
globally and for broad regions through
the 21st century (Meehl et al. 2007, p.
753; Randall et al. 2007, pp. 596–599),
and reported these projections using a
framework for characterizing certainty
(Solomon et al. 2007, pp. 22–23).
Examples include: (1) It is virtually
certain there will be warmer and more
frequent hot days and nights over most
of the earth’s land areas; (2) it is very
likely there will be increased frequency
of warm spells and heat waves over
most land areas, and the frequency of
heavy precipitation events will increase
over most areas; and (3) it is likely that
increases will occur in the incidence of
extreme high sea level (excludes
tsunamis), intense tropical cyclone
activity, and the area affected by
droughts (IPCC 2007b, p. 8, Table
SPM.2). More recent analyses using a
different global model and comparing
other emissions scenarios resulted in
similar projections of global temperature
change across the different approaches
(Prinn et al. 2011, pp. 527, 529).
All models (not just those involving
climate change) have some uncertainty
associated with projections due to
assumptions used, data available, and
features of the models; with regard to
climate change this includes factors
such as assumptions related to
emissions scenarios, internal climate
variability and differences among
models. Despite this, however, under all
global models and emissions scenarios,
the overall projected trajectory of
surface air temperature is one of
increased warming compared to current
conditions (Meehl et al. 2007, p. 762;
Prinn et al. 2011, p. 527). Climate
models, emissions scenarios, and
associated assumptions, data, and
analytical techniques will continue to
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be refined, as will interpretations of
projections, as more information
becomes available. For instance, some
changes in conditions are occurring
more rapidly than initially projected,
such as melting of Arctic sea ice
(Comiso et al. 2008, p. 1; Polyak et al.
2010, p. 1797), and since 2000 the
observed emissions of greenhouse gases,
which are a key influence on climate
change, have been occurring at the midto higher levels of the various emissions
scenarios developed in the late 1990’s
and used by the IPPC for making
projections (e.g., Raupach et al. 2007,
Figure 1, p. 10289; Manning et al. 2010,
Figure 1, p. 377; Pielke et al. 2008,
entire). Also, the best scientific and
commercial data available indicates that
average global surface air temperature is
increasing and several climate-related
changes are occurring and will continue
for many decades even if emissions are
stabilized soon (e.g., Meehl et al. 2007,
pp. 822–829; Church et al. 2010, pp.
411–412; Gillett et al. 2011, entire).
Changes in climate can have a variety
of direct and indirect impacts on
species, and can exacerbate the effects
of other threats. Rather than assessing
‘‘climate change’’ as a single threat in
and of itself, we examine the potential
consequences to species and their
habitats that arise from changes in
environmental conditions associated
with various aspects of climate change.
For example, climate-related changes to
habitats, predator-prey relationships,
disease and disease vectors, or
conditions that exceed the physiological
tolerances of a species, occurring
individually or in combination, may
affect the status of a species.
Vulnerability to climate change impacts
is a function of sensitivity to those
changes, exposure to those changes, and
adaptive capacity (IPCC 2007, p. 89;
Glick et al. 2011, pp. 19–22). As
described above, in evaluating the status
of a species, the Service uses the best
scientific and commercial data
available, and this includes
consideration of direct and indirect
effects of climate change. As is the case
with all potential threats, if a species is
currently affected or is expected to be
affected by one or more climate-related
impacts, this does not necessarily mean
the species is a threatened or
endangered species as defined under the
Act. If a species is listed as threatened
or endangered, this knowledge
regarding its vulnerability to, and
impacts from, climate-associated
changes in environmental conditions
can be used to help devise appropriate
strategies for its recovery.
While projections from global climate
model simulations are informative and
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in some cases are the only or the best
scientific information available, various
downscaling methods are being used to
provide higher-resolution projections
that are more relevant to the spatial
scales used to assess impacts to a given
species (see Glick et al, 2011, pp. 58–
61). With regard to the area of analysis
for the pygmy-owl, downscaled models
predict that the Sonoran Desert
Ecoregion will be drier through the 21st
century and that the transition to a more
arid climate is likely already under way
(Seager et al. 2007, p. 1181). Future
drought is projected to occur under
warmer temperature conditions as
climate change progresses. Seager et al.
(2007, p. 1181) predict that the recent
multiyear droughts, the Dust Bowl, and
1950s drought conditions will become
the new climatology of the American
Southwest with a timeframe of years to
decades. Already, the current, multiyear
drought in the western United States,
including most of the Southwest, is the
most severe drought recorded since
1900 (Overpeck and Udall 2010, p.
1642).
Although specifically looking at
pinyon-juniper communities, Breshears
et al. (2005, pp. 15147–15148) showed
that a particular concern under these
drought conditions is regional-scale
mortality of overstory trees, which
rapidly alters ecosystem type, associated
ecosystem properties, and land-surface
conditions for decades. Woodlands
providing important pygmy-owl habitat,
including meso- and xeroriparian trees,
thornscrub, and tropical deciduous
forests may respond in a similar
manner. Gitlin et al. (2006, p. 1482)
documented increased mortality of
Populus fremontii (Fremont
cottonwood) (an important riparian tree
in Sonoran Desert mesoriparian
communities) during the recent drought.
Northern areas of Mexico are most
vulnerable to droughts and
desertification because erosion and
drought severity will increase with
higher temperatures and rainfall
variations in these arid and semi-arid
regions (Conde and Gay 1999, p. 2). The
three Mexican regions most vulnerable
to climate change are, in order of
importance, Central, Northern (in areas
occupied by pygmy-owls), and the
Tabasco Coast (Conde and Gay 1999, p.
2). Magana and Conde (2000, p. 183)
showed the vulnerability of northern
Mexico, specifically Sonora, to
interannual climate variability and
climate change. They found that future
major challenges that will result from
climate change are increasing demand
for water, competition among water
users, and decline in water quality,
along with the resultant loss or
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reduction of riparian woodlands and
other pygmy-owl habitat elements.
Smith et al. (2000, p. 79) noted the
following with regard to nonnative grass
invasions and climate change, ‘‘This
shift in species composition in favor of
exotic annual grasses, driven by global
[climate] change, has the potential to
accelerate the fire cycle, reduce
biodiversity, and alter ecosystem
function in the deserts of western North
America.’’
Changes in the timing of precipitation
due to climate change may have effects
related to pygmy-owl prey availability
and abundance. Flesch (2008, p. 8)
found that timing and quantity of
precipitation affected both lizard and
rodent abundance in ways that
suggested rainfall is an important driver
of population and community
dynamics. In general, cool-season
rainfall had a positive correlation with
rodent populations and warm-season
rainfall was positively correlated with
lizard populations. Because various
climate change models predict that
climate conditions will become more
variable, lizard species that are most
affected by variations in precipitation
will tend to decline in abundance across
time. This is an important finding given
that lizards are the primary prey item
for pygmy-owls during the summer.
The majority of the current range of
the pygmy-owl occurs in tropical or
subtropical vegetation communities that
may be reduced in coverage if climate
change results in hotter, more arid
conditions. The Sonoran Desert
Ecoregion is already characterized by
hot, arid conditions, and pygmy-owls in
this portion of the range are already
adapted to the hotter, more arid
conditions that may prevail in the
future. This adaptation may be
important to the continued existence of
the subspecies as desertification spreads
in response to climate change, but may
be offset as some future model scenarios
predict a reduction in columnar cacti
densities, the primary pygmy-owl
nesting substrate within the Sonoran
Desert Ecoregion (Weiss and Overpeck
2005, p. 2074). Already studies have
documented a noticeable shift north of
bird species in association with
changing climates. Christmas Bird
Count data show a shift northward in 56
percent of the 305 most widespread,
regularly occurring wintering bird
species (NABCI 2010). This same report
indicates that bird species that are rare
or nonexistent in the United States at
present will expand their ranges into
our country from the south (NABCI
2009, p. 15).
Climate change may have a negative
impact on some pygmy-owl populations
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because it will exacerbate the current
and ongoing effects discussed above.
For example, drought has been
documented in Arizona and northern
Sonora to reduce juvenile pygmy-owl
survival. Under the predicted climate
change scenarios, drought will occur
more frequently and increase in
severity. The invasion of nonnative
species has been documented in the loss
of pygmy-owl habitat and native
vegetation communities. A common
prediction under climate change is for
conditions that will favor the increased
occurrence and distribution of
nonnative species. Riparian areas, both
permanent and ephemeral, support
important pygmy-owl habitat elements
such as thermal and predator cover, and
increased prey availability. Precipitation
events under most climate change
scenarios will decrease in frequency and
increase in severity. This may reduce
available cover and prey for pygmy-owls
by affecting riparian areas through
scouring flood events and reduced
moisture retention. However, the extent
to which changing climatic patterns will
affect the pygmy-owl is not known with
certainty at this time.
Hurricanes
Although not generally considered a
historical impact to pygmy-owl habitat,
the loss of habitat and nest structures as
a result of hurricanes has recently been
identified as a potential contributor to
an apparent decline in pygmy-owl
nestlings documented as part of an
ongoing pygmy-owl nest box study in
south Texas (Proudfoot 2011b, p. 1;
Proudfoot 2010, p. 1). Hurricanes within
the past five years have impacted
thousands of acres of occupied pygmyowl habitat by removing trees and
reducing cover and structural diversity.
Within the current range of the pygmyowl, hurricanes are most likely to affect
pygmy-owl habitat in southern Texas
and northeastern Mexico, although
hurricanes in the Pacific Ocean also
have the potential to affect pygmy-owl
habitat in western Mexico. Historically,
major hurricanes have made landfall in
southern Texas on average about once
every decade. However, more recently,
hurricanes (Erika in 2003, Dolly in 2008,
and Alex in 2010) have occurred more
often than in the past, suggesting that
major hurricanes may be occurring more
frequently now. If hurricanes continue
to occur every few years, this frequency
of hurricanes resulting in loss of
woodlands may not allow some areas of
previously suitable pygmy-owl habitat
to regenerate trees of adequate size to
support the cavities needed for nesting
by pygmy-owls. However, the effects are
expected to be localized.
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Scattered, Small Population Groups
An important principle of
conservation genetics is that small,
isolated populations will experience
reductions in the health of the
population due to the expression of
negative population characteristics as a
result of inbreeding. Loss of individual
adaptation can also occur and may
adversely affect population demography
and increase the risk of population
extinction (Caughley 1994, p. 217).
Inbreeding in small, isolated
populations often occurs because of a
lack of mates to choose from, not from
preferential mating among related
individuals. This can lead to increased
chances that both parents will
contribute genes containing harmful
traits, some of which may affect
important adaptive and physiological
characteristics, such as survival,
fertility, and physiological vigor (Soule
and Mills 1998, p. 1658).
Inbreeding has been documented
within the small pygmy-owl population
in Arizona (Abbate et al. 2000, p. 21).
Lack of genetic diversity has also been
documented during recent genetics
studies (Proudfoot and Slack 2001, pp.
5–7). Loss of isolated population groups
has occurred in Arizona due to lack of
productivity and inadequate dispersal
(AGFD 2008, p. 1). In 2008, a possible
genetic heart condition was diagnosed
in the mortality of three related pygmyowls in the captive breeding research
project, a possible expression of the
detrimental effects of the inbreeding of
pygmy-owls in Arizona (Fox 2008, p. 1).
In addition to genetic factors, habitat
degradation or human-caused mortality
can cause shifts in population
characteristics that drive population
decline. Genetic factors may simply
hasten the extinction process once a
population is small (Miller and Waits
2003, p. 4334). In the face of ongoing
loss and fragmentation of habitat, the
potential for inbreeding increases as
populations or groups of pygmy-owls
are increasingly isolated. This increases
the need for management that
maintains, restores, or substitutes for
historical patterns of betweenpopulation gene flow (Hogg et al. 2006,
p. 1491). In addition to inbreeding,
genetic drift (a change in the gene pool
of a population that takes place strictly
by chance) in small populations can
depress population fitness and increase
extinction risk (Tallmon et al. 2004, p.
489), as well as diminish future
adaptations to a changing environment
(Lande 1988, p. 1455). A significant loss
in genetic variation within small
populations may decrease population
health or limit the long-term capacity of
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a population to respond to
environmental challenges (Keller et al.
1994).
Similarly, chance environmental and
demographic events may pose a more
substantial threat to small populations
than to large populations (Westemeier et
al. 1998, p. 1695). Caughley and Gunn
(1996, p. 166) noted that small
populations can become extinct entirely
by chance even when their members are
healthy and the environment favorable.
Demographic characteristics of small
populations can be significant
contributors in determining minimum
viable population sizes. Viability of
small populations is likely dependent
on both demography and population
genetics and should not be considered
independently (Keller et al. 2002, p.
356; Lande 1988, p. 1459).
Consequently, for those areas of the
pygmy-owl’s range where local small
population size is an issue, if the result
of any of the above factors negatively
affects pygmy-owl demography or
genetics, effects, at least at the local
population scale, may be significant.
Genetic rescue within a
metapopulation structure can occur
through periodic immigration into
small, inbred, at-risk populations and
can alleviate inbreeding depression and
boost fitness, but habitat connectivity
and adequate dispersal opportunities
must be present. However, immigration
of genetically divergent individuals can
lead to the opposite effect—a reduction
in population fitness due to outbreeding
depression (when crosses between
individuals from different populations
have lower fitness than progeny from
crosses between individuals within the
same population) (Tallmon et al. 2004,
p. 489).
In conclusion, small population size
and inadequate dispersal, as well as a
reduced ability to adapt due to low
genetic diversity, can result in increased
vulnerability of extinction for pygmyowls in small, isolated populations. The
best information we have indicates that
small, isolated populations probably
occur in Arizona, Texas, and
northeastern Mexico. We know of no
small, isolated populations in southern
Mexico, and thus conclude that small
population size is not likely to be a
threat in that area.
pygmy-owl populations from factors
related to drought and small population
size have been documented in portions
of the pygmy-owl’s range, specifically
Arizona. All but one model evaluating
changing climatic patterns for the
southwestern United States and
northern Mexico predict a drying trend
for the region (Seager et al. 2007, pp.
1181–1184), which will negatively affect
riparian and other plant communities
that provide habitat for pygmy-owls.
The extent to which changing climatic
patterns will affect the pygmy-owl is not
known with certainty at this time.
However, predicted impacts of climate
change may exacerbate and intensify the
effects of long-term drought and other
negative impacts within the range of the
pygmy-owl identified under Factor A.
One concern in the northwestern
portion of the species’ range is the
potential decline in large columnar
cacti, an essential pygmy-owl habitat
element that provides nest sites.
However, given the persistence of
pygmy-owl populations in the more arid
areas of its range (northwestern Mexico
and Arizona), pygmy-owls in these areas
may provide the genetic adaptations
necessary to adapt to changing
conditions.
Given the current pygmy-owl
population status, the effects of small
population size are likely to continue,
especially in the northern portion of the
range. Reduced population connectivity
as a result of habitat impacts identified
under Factor A will likely continue to
increase the potential for inbreeding and
the associated loss of genetic diversity.
At least in Arizona, lack of dispersing
juveniles and floating nonbreeding
individuals in the population due to
low numbers of breeding pygmy-owls
will also affect long-term occupancy of
breeding territories and further erode
the metapopulation structure in Arizona
and northern Sonora. However, these
effects appear to be localized, and we do
not find that impacts under Factor E are
significantly affecting pygmy-owls
rangewide. Based upon our review of
the best commercial and scientific data
available, we conclude that other
natural and manmade factors are not
immediate threats to the pygmy-owl
rangewide, and are not likely to become
so in the future.
Summary of Factor E
In summary, direct, human-caused
mortality of pygmy-owls can occur and
may, locally, have some impact on
isolated population segments. However,
it is unlikely that direct human-caused
mortality will have significant
population-level impacts on the pygmyowl throughout its range. Impacts to
Pygmy-Owl Finding Throughout Its
Range
As required by the Act, we conducted
a review of the status of the species and
considered the five factors from section
4(a) in assessing whether the pygmy-owl
is threatened or endangered throughout
all of its range. We examined the best
scientific and commercial information
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available regarding the past, present,
and future threats faced by the species.
We reviewed the petition, information
available in our files, other available
published and unpublished
information, and we consulted with
species and subject experts, including
peer review, and other Federal, State,
Tribal, and local agencies.
In considering what factors might
constitute threats, we must look beyond
the mere exposure of the species to the
factor and determine whether the
species responds to the factor in a way
that causes actual impacts to the
species. If there is exposure to a factor,
but no response, or only a positive
response, that factor is not a threat. If
there is exposure and the species
responds negatively, the factor may be
a threat and we then attempt to
determine how significant a threat it is.
If the threat is significant, it may drive
or contribute to the risk of extinction of
the species such that the species
warrants listing as threatened or
endangered as those terms are defined
by the Act. This does not necessarily
require empirical proof of a threat. The
combination of exposure and some
corroborating evidence of how the
species is likely impacted could suffice.
The mere identification of factors that
could impact a species negatively is not
sufficient to compel a finding that
listing is appropriate; we require
evidence that these factors are operative
threats that act on the species to the
point that the species meets the
definition of threatened or endangered
under the Act.
Through our five-factor analysis, we
identified a number of factors that are
negatively affecting the pygmy-owl,
including the following: (1) Habitat loss
and fragmentation due to urbanization,
improper grazing, nonnative-species
invasions and associated changes in fire
regimes, OHV use, agricultural
development, and wood cutting; (2)
border issues; (3) inadequate regulatory
mechanisms; (4) drought and climate
change; and (5) small size of some local
populations. To determine whether
these factors individually or collectively
rise to a ‘‘threat’’ level such that the
pygmy-owl is in danger of extinction
throughout its range, or likely to become
so in the foreseeable future, we first
considered whether these negative
factors to the subspecies were causing
long-term, range-wide, population-scale
declines in pygmy-owl numbers, or
were likely to do so in the foreseeable
future.
While range-wide surveys have not
been conducted for the pygmy-owl,
information from surveys that have been
conducted in Texas and Arizona in the
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United States, and in Sinaloa and
Sonora in Mexico can be used to help
us determine the general population
status of the pygmy-owl throughout its
range. The best available information we
have indicates that local populations of
pygmy-owls in Arizona, northern
Sonora, and Texas have likely
experienced population declines;
however, the pygmy-owl is still found
in these areas. Pygmy-owls are still
found in southern Mexico, and the best
available information indicates that they
may remain relatively common
throughout this area. Based on the level
of information we do have, it appears
pygmy-owls persist in most areas where
they have been historically documented
in the literature and during recent
survey efforts. The most recent IUCN
(International Union for Conservation of
Nature) Red List (an international
standard for species extinction risk)
contains the following statement with
regard to the status of the ferruginous
pygmy-owl, ‘‘Despite the fact that the
population trend appears to be
decreasing, the decline is not believed
to be sufficiently rapid to approach
thresholds for Vulnerable under the
population trend criterion (greater than
a 30 percent decline over ten years or
three generations).’’ (IUCN 2008, p. 2).
So, while this statement may be an
indication of a range-wide population
decline, it does not appear that such a
decline is significant enough to place
the pygmy-owl in a category of concern
for IUCN. In addition, this statement
applies to ferruginous pygmy-owls as a
species, and does not separate status for
the individual subspecies. Therefore,
based on the best available scientific
and commercial information, we do not
find evidence of a sufficient declining
trend in the subspecies’ population to
indicate it is in danger of range-wide
extinction now, or in the foreseeable
future. In other words, based on a
review of the best available data, the
data do not suggest that the combined
effects of the negative impacts discussed
in our five-factor analysis are resulting
in an overall, long-term reduction in the
distribution of the pygmy-owl, or an
associated significant range-wide
decline in pygmy-owl numbers, such
that the subspecies is currently in
danger of extinction or likely to become
so.
There are severe impacts to certain
portions of the pygmy-owl’s range.
However, those impacts are restricted to
a relatively small (27 percent) portion of
the entire range. We found no evidence
that these impacts are of sufficient
magnitude and severity to affect the
rangewide population of pygmy-owls.
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Although it appears there are localized
declines in pygmy-owl populations in
Arizona and, possibly Texas and
northern Sonora, there does not appear
to be an ongoing, significant, long-term
decline in range-wide pygmy-owl
numbers that would lead us to believe
the subspecies is currently in danger of
extinction or likely to become so
throughout its range due to factors
identified in our five-factor analysis.
We also considered whether any of
the negative impacts began recently
enough that their effects are not yet
manifested in current subspecies’
population numbers, but are likely to
have an effect in the foreseeable future.
Impacts from climate change are a
particular impact that has recently been
accelerating. These effects are so recent
that we have no information on the
long-term effects to pygmy-owl
populations. However, drought is
predicted to become more prevalent
within the Sonoran range of the pygmyowl, and drought has had a historicallynegative impact on pygmy-owl
populations in this area. The
predictions of drought throughout the
remainder of the range are uncertain;
however, as discussed under Factor E,
pygmy-owls in the northern portion of
their range may be more resilient and
better adapted to drought conditions.
Other impacts are largely limited to
specific portions of the subspecies’
range, and we do not believe they would
manifest their future effects as rangewide population declines. Therefore,
the pygmy-owl is not currently in
danger of extinction, or likely to become
so, due to potential threats that began
recently enough that their long-term
effects are not yet manifest.
Next, we considered whether any of
the current negative factors are likely to
increase within the foreseeable future,
such that the species is likely to become
in danger of extinction in the
foreseeable future. We do believe that
some of the negative factors identified
will increase in the foreseeable future
including urbanization, nonnative
invasions and fires, agricultural
development, woodcutting, grazing, and
climate extremes. However, as
discussed above in our five-factor
analysis, these impacts occur in a
limited portion of the range, primarily
Arizona, Texas, and Sonora. For the
remaining portions of Mexico, the best
available information indicates that the
negative factors are less severe or that
there is no evidence of the negative
impact. The best available information
also indicates that pygmy-owls are
relatively common in this portion,
which is 73 percent of their range.
Therefore, we conclude that there is no
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evidence that negative factors, such as
urbanization, agricultural development,
or woodcutting, will increase in the
foreseeable future in the majority of the
pygmy-owl’s range.
Finally, we considered whether
stochastic events might decrease the
long-term viability of the species
(species viability requires a naturallyreproducing population large enough to
maintain sufficient genetic variation to
provide for its continued evolution and
response to natural environmental
changes). We considered whether, given
a currently stable population rangewide, is the pygmy-owl likely to become
in danger of extinction in the
foreseeable future because stochastic
events might reduce its current numbers
to a point where its long-term viability
would be in question. Current
information suggests that stochastic
events such as hurricanes, extreme
drought, and catastrophic fires could
reduce the viability of local pygmy-owl
populations in Arizona, Texas, and
northern Sonora. However, because of
the pygmy-owl’s wide distribution and
historical indications of relatively
higher numbers throughout most of its
range, even if a stochastic event were to
occur within the foreseeable future that
negatively affected this subspecies, the
range-wide population would still be
unlikely to fall to such a low level that
it would be in danger of extinction.
Despite some regional declines in
pygmy-owl population numbers, the
subspecies has been able to maintain
what appears to be range-wide
population viability. Negative factors
affecting pygmy-owls seem to be
restricted, for the most part, to a
relatively small portion of its range. The
areas where we have detailed
information to evaluate potential threats
and pygmy-owl population status
(Arizona, Texas, and Sonora) represent
approximately 27 percent of the overall
pygmy-owl range. The best available
information suggests that the range-wide
pygmy-owl population is not
significantly declining, despite regional
changes in population numbers, and
that most of the immediate impacts to
the pygmy-owl and its habitats are
geographically concentrated. In
summary, based on our review of the
best available scientific and commercial
information pertaining to the five
factors, we find that threats throughout
the majority of the pygmy-owl’s range
are not of sufficient imminence,
severity, or magnitude to indicate that
the pygmy-owl is in danger of extinction
(endangered), or likely to become
endangered within the foreseeable
future (threatened), throughout all of its
range.
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After determining the subspecies is
not currently in danger of extinction or
likely to become so in the foreseeable
future throughout its range, we next
consider whether a distinct vertebrate
population segment (DPS) or whether
any significant portion of the pygmy
owl’s range is in danger of extinction or
is likely to become so in the foreseeable
future.
Distinct Vertebrate Population Segment
Under the Service’s Policy Regarding
the Recognition of Distinct Vertebrate
Population Segments Under the
Endangered Species Act (61 FR 4722,
February 7, 1996), three elements are
considered in the decision concerning
the establishment and classification of a
possible DPS. These are applied
similarly for additions to or removal
from the Federal List of Endangered and
Threatened Wildlife. These elements
include:
(1) The discreteness of a population in
relation to the remainder of the species
to which it belongs;
(2) The significance of the population
segment to the species to which it
belongs; and
(3) The population segment’s
conservation status in relation to the
Act’s standards for listing. delisting, or
reclassification (i.e., is the population
segment endangered or threatened).
Discreteness
Under the DPS policy, a population
segment of a vertebrate taxon may be
considered discrete if it satisfies either
one of these conditions:
(1) It is markedly separated from other
populations of the same taxon as a
consequence of physical, physiological,
ecological, or behavioral factors.
Quantitative measures of genetic or
morphological discontinuity may
provide evidence of this separation.
(2) It is delimited by international
governmental boundaries within which
differences in control of exploitation,
management of habitat, conservation
status, or regulatory mechanisms exist
that are significant in light of section
4(a)(1)(D) of the Act.
Significance
If a population segment is considered
discrete under one or more of the
conditions described in the Service’s
DPS policy, its biological and ecological
significance will be considered in light
of Congressional guidance that the
authority to list DPSs be used
‘‘sparingly’’ while encouraging the
conservation of genetic diversity. In
making this determination, we consider
available scientific evidence of the
discrete population segment’s
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importance to the taxon to which it
belongs. Since precise circumstances are
likely to vary considerably from case to
case, the DPS policy does not describe
all the classes of information that might
be used in determining the biological
and ecological importance of a discrete
population. However, the DPS policy
describes four possible classes of
information that provide evidence of a
population segment’s biological and
ecological importance to the taxon to
which it belongs. As specified in the
DPS policy (61 FR 4722), this
consideration of the population
segment’s significance may include, but
is not limited to, the following:
(1) Persistence of the discrete
population segment in an ecological
setting unusual or unique to the taxon;
(2) Evidence that loss of the discrete
population segment would result in a
significant gap in the range of a taxon;
(3) Evidence that the discrete
population segment represents the only
surviving natural occurrence of a taxon
that may be more abundant elsewhere as
an introduced population outside its
historic range; or
(4) Evidence that the discrete
population segment differs markedly
from other populations of the species in
its genetic characteristics.
A population segment needs to satisfy
only one of these conditions to be
considered significant. Furthermore,
other information may be used as
appropriate to provide evidence for
significance.
Analysis of Potential Distinct
Population Segments
The petitioners requested that we
consider two potential DPS’s of the
pygmy-owl for protection under the Act,
a Sonoran Desert DPS and an Arizona
DPS. The petitioners did not suggest any
additional DPS configurations to be
evaluated. However, in order to be
complete in our analysis of potentially
listable pygmy-owl entities, we also
considered other potential DPS
configurations including an eastern/
western DPS and a Texas DPS. Our
analysis of these two other potential
DPS configurations follows our
evaluation of the petitioned DPS
configurations.
Potential Sonoran Desert DPS
As described, none of the boundaries
of the petitioner’s Sonoran Desert DPS
include an international border or
boundary (CBD and DOW 2007, pp. 4–
6) (Figure 4). Therefore, the petitioned
DPS must meet the first condition for
discreteness in order to be considered a
valid DPS, because it does not meet the
second condition. The eastern and
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western portions of the range of the
pygmy-owl are separated by the Sierra
Madre and other mountain ranges in
north-central Mexico (Proudfoot et al.
2006a, p. 9). However, there are no
obvious physical or geographic barriers
that separate the petitioned Sonoran
Desert DPS from the rest of the pygmyowl’s range to the south. There is a
documented area in central Sonora, near
Hermosillo, Mexico, that may act as an
impediment to pygmy-owl movements
and dispersal, because of the lack of
contiguous suitable habitat resulting
from natural and artificial conditions
(Flesch 2003, pp. 40, 100). However, the
extent of this band of unsuitable habitat
does not prevent regular or occasional
movements by pygmy-owls between
northern and southern Sonora. This is
supported by genetic sampling and
analysis that has recently been
completed, that indicates that there is
likely gene flow between the two groups
(Proudfoot 2009a, p. 1).
Proudfoot’s earlier assessment of
mitochondrial DNA (mtDNA) and
microsatellite DNA of pygmy-owls from
Arizona, Sonora, and Sinaloa implied
restricted gene flow between the
Sonoran and Sinaloan populations
(Proudfoot et al. 2006a, p. 10; Proudfoot
et al. 2006b, p. 9). However, the authors
implied that limited sampling and
geographic distance between sample
sites in Sonora and Sinaloa may have
influenced the results of these studies.
To verify the inference of restricted gene
flow, a joint effort among Proudfoot,
AGFD, and the Service resulted in the
collection and analysis of an additional
119 samples collected in areas not
previously sampled (Proudfoot 2009, p.
1; AGFD 2008a, pp. 1–10). Analysis of
the genotypic variation revealed
isolation by distance with significant
gene flow between pygmy-owl
populations. Estimates of migrants per
generation time for pygmy-owl
populations were 8.62 (Arizona-Sonora),
6.65 (Arizona-Sinaloa) and 23.46
(Sonora-Sinaloa) (Proudfoot 2009, p. 1).
So, while no haplotypes from
Arizona, Sonora, or Sinaloa are shared
with the remainder of Mexico and
Texas, there are shared haplotypes
among Arizona, Sonora, and Sinaloa,
indicating there is exchange of genetic
material within this grouping (Proudfoot
et al. 2006a, p. 7). This would argue
against the Sonoran Desert Ecoregion
being markedly separate from the
remainder of Sonora and Sinaloa. Based
on observations of pygmy-owls during
survey and capture activities in Arizona,
and in both northern and southern
Sonora as described above, the best
available scientific and commercial data
does not indicate that there is any
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evidence that there are marked
behavioral, morphological, or
physiological differences within the
petitioned DPS (AGFD 2008a, pp. 1–4).
As a result, this study indicates that
there is no marked genetic or
morphological separation between the
petitioned Sonoran Desert DPS and
southern Sonora populations (Proudfoot
2009a, p. 1; AGFD 2008a, p. 10).
The Sonoran Desert Ecoregion does
differ ecologically from the remainder of
the areas within its range. Despite the
fact that occurrence of some plant
species overlaps with other ecoregions
to the south and east, the Sonoran
Desert is a unique dry desert area that
does function ecologically in a different
way when compared to adjacent
ecoregions. However, as described
above, the best available scientific and
commercial data do not indicate that
this ecological difference has resulted in
any morphological, physiological, or
genetic differentiation within pygmyowl populations in the Sonoran Desert.
Environmental characteristics within
the Sonoran Desert have likely resulted
in the reduced numbers and densities of
pygmy-owls found in this area.
However, this does not appear to have
resulted in any physical differentiation,
at least anecdotally, from adjacent
pygmy-owl populations.
We find that there is no evidence that
the Sonoran Desert population of
pygmy-owl is markedly separated in any
way from the remainder of the taxon.
Therefore, we determine, based on a
review of the best available information,
that the petitioned Sonoran Desert DPS
of the pygmy-owl does not meet the
discreteness conditions of the 1996 DPS
policy. As such, this population
segment does not qualify as a DPS under
our policy and is not a listable entity
under the Act.
The DPS policy indicates that
significance should be analyzed only if
a population segment has been
identified as discrete. Because we found
that the Sonoran Desert population
segment did not meet the discreteness
element and, therefore, does not qualify
as a DPS under the Service’s DPS
policy, we will not conduct an
evaluation of significance.
Potential Arizona DPS
Because we are evaluating this
petitioned entity based on the currently
accepted taxonomic classification of the
pygmy-owl (see Description and
Taxonomy section above), the taxon
considered in this finding is the same as
for our 1997 listing of the pygmy-owl
(62 FR 10730). Consequently, the
petitioned Arizona DPS is exactly the
same DPS configuration that was the
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subject of litigation and, ultimately, the
same DPS configuration that the Service
removed from the Federal List of
Endangered and Threatened Wildlife in
2006 (71 FR 19452; April 24, 2006)
(Figure 4). That final rule presents our
analysis showing that, while the
discreteness criteria for the DPS were
met, we could not show that this DPS
was significant to the taxon as a whole.
The petition states that ‘‘the Arizona
DPS occurs in a unique ecological
setting and differs markedly in its
genetic characteristics from pygmy-owls
in Sinaloa and elsewhere in the species
range. Loss of the Arizona DPS would
also create a significant gap in the
species’ range, resulting in loss of
roughly a third of the subspecies’ range,
and half of the species’ range in the
Sonoran Desert. The Arizona DPS is also
significant because it represents the
entire range of G. ridgwayi cactorum in
the United States’’ (CBD and DOW 2007,
p. 12).
Our analysis in the final rule to delist
the pygmy-owl showed that the thenlisted Arizona DPS of the pygmy-owl
was not markedly different in its genetic
characteristics from pygmy-owls in
northern Sonora, Mexico; did not occur
in a unique ecological setting; nor
would loss of the DPS represent a
significant gap in the range of the taxon
(71 FR 19452). We are unaware of any
scientific information compiled since
the delisting that would alter the
conclusions made in that final rule.
Therefore, we determine, based on a
review of the best available information,
that the petitioned Arizona DPS of the
pygmy-owl does not meet the
significance conditions of the 1996 DPS
policy. Therefore, this population
segment does not qualify as a DPS under
our policy and is not a listable entity
under the Act.
Potential Texas DPS
We have reviewed new information
regarding the status of the pygmy-owl in
Texas (Proudfoot 2010, p. 1; 2011b, p.
1). In addition, the peer reviewers of the
current genetic information provided
insight and recommendations regarding
the genetic diversity and management of
pygmy-owls in Arizona and Texas.
Upon consideration of this new
information, we concluded that it was
appropriate to evaluate a potential
Texas DPS that includes the current
range of the pygmy-owl in Texas to the
international border with Mexico.
Discreteness
The use of the international border to
define discreteness of the Arizona
pygmy-owl DPS was upheld by the
courts (No. 02–15212, CV00–0903 SRB
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at 11586, 2003) because of the
differences in status and management of
the pygmy-owl between Arizona and
Mexico. Defining the discreteness of the
Texas DPS is appropriate using the same
rationale. For example, Mexico has no
regulations or laws specifically
protecting the pygmy-owl. In Texas, the
pygmy-owl is listed as threatened, and
State law prohibits take without the
appropriate permit. Therefore, we
determine that the Texas DPS is discrete
due to differences in status and
management of the pygmy-owl between
the United States, in Texas, and Mexico.
Significance
The best available scientific and
commercial information does not
indicate that the Texas population of
pygmy-owls occurs in an ecological
setting that is unusual or unique to the
taxon. For example, the vegetation
community that supports pygmy-owls
in Texas is classified as Tamaulipan
brushland (Jahrsdoerfer and Leslie 1988,
p. 1). This vegetation community and
the associated pygmy-owl habitat
elements are found in southern Texas
and northeastern Mexico (Jahrsdoerfer
and Leslie 1988, pp. 1–9; Hunter 1988,
p. 8; Cook et al. 2001, pp. 1–2) and
comprise most of the eastern portion of
the pygmy-owl’s current range. Texas
represents approximately 15 percent of
the eastern portion of the range of the
pygmy-owl. In other words,
approximately 85 percent of the pygmyowl habitat that is characterized as
Tamaulipan brushland occurs outside of
Texas. Therefore, the Texas population
of pygmy-owls does not occur in an
unusual or unique setting for the taxon.
Texas represents approximately 5
percent of the overall range of the
pygmy-owl. From a geographic
perspective, loss of this portion of the
range does not represent a significant
gap in the range of the pygmy-owl.
However, we must also consider where
the loss of the contribution of this
population segment to overall
population numbers would represent a
significant gap in the range. Pygmy-owl
population estimates for Texas range
from 100 owls in Kleberg County
(Tewes 1992, p. 24), to 654 pairs in
Kenedy, Brooks, and Willacy Counties
(Wauer et al. 1993, p. 1074), and 745 to
1,823 pygmy-owls on ranches in Kenedy
and Brooks Counties (Mays 1996, p. 32).
This is considerably higher than
population estimates in Arizona
(approximately 50 owls (Abbate et al.
2000, pp. 15–16)), but likely similar to
the densities occurring in thornscrub
and dry tropical forest habitats further
south in Mexico. Field data indicate that
pygmy-owls in the southern portions of
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Sonora (within thornscrub and tropical
deciduous forests) are common and
likely number on the order of
thousands, while further north within
the Sonoran Desert Ecoregion, they are
fewer in number, more patchily
distributed, and likely number on the
order of hundreds (Flesch 2003, pp. 39–
42; AGFD 2008a, p. 6). Given that the
majority of the pygmy-owl’s range
appears to support similar numbers and
densities of pygmy-owls as Texas, we do
not believe that the loss of the
population in Texas would represent a
significant gap from the perspective of
contribution to overall pygmy-owl
population numbers.
While there is some evidence that the
Texas population of pygmy-owls
contributes key genetic diversity to the
overall population of pygmy-owls and
is, to some extent, genetically unique
(Proudfoot 2006a, p. 7; Cicero 2008, p.
2; Oyler-McCance 2008, pp. 1–2;
Dumbacher 2008, p. 9), the best
available scientific and commercial
information suggests that pygmy-owls in
Texas are genetically similar to pygmyowls across the international border in
Mexico (Proudfoot 2006a, pp. 9–10).
This lack of genetic differentiation from
adjacent pygmy-owl populations
suggests that the Texas population
segment does not differ markedly from
adjacent populations of pygmy-owls.
Proudfoot et al. (2006a, p. 7) indicated
that Texas is characterized by a single
haplotype; and that one haplotype is
shared with pygmy-owls from
Tamaulipas, Mexico, indicating there
has been some exchange of genetic
material. Based on the best available
scientific and commercial information,
we do not find that the Texas DPS is
significant to the taxon as a whole, and
is, therefore, not a listable entity under
the Act. No further analysis of the Texas
DPS is warranted at this point.
Potential Western and Eastern DPSs
Discreteness
The current range of the pygmy owl,
as discussed above, is defined as
occurring from lowland central Arizona
south through western Mexico to the
´
States of Colima and Michoacan, and
from southern Texas south through the
Mexican States of Tamaulipas and
Nuevo Leon (Johnsgard 1988, p. 159;
Millsap and Johnson 1988, p. 137;
Oberholser 1974, p. 452; Friedmann et
al. 1950, p. 145), consistent with the last
American Ornithologist Union (AOU)
list that addressed avian classification to
the subspecies level (AOU 1957). In the
United States, the eastern and western
portions of the pygmy-owl’s range are
separated by over 1,600 km (1,000 mi)
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of unsuitable habitat (Chihuahuan
desert and grasslands, oak and pine
forests) and elevations greater than
1,200 m (4,000 ft) associated with
various mountain ranges. There has
never been any record of occurrence for
pygmy-owls in the area between south
Texas and Tucson, Arizona. In Mexico,
this distribution is separated throughout
its entirety by the Sierra Madre
Occidental and the Sierra Madre
Oriental. These mountain ranges extend
south beyond the southern boundary of
the described range of this subspecies
and represent a significant geographical
barrier between the eastern and western
segments of the distribution (Cartron et
al. 2000, p. 6). The elevational range of
peaks in these mountain ranges is from
1,880 m to over 3,600 m (6,000 ft to over
12,000 feet). Given the elevational limits
of the pygmy-owl’s distribution within
its range (Freidman et al. 1950, pp. 145–
147), and the fact that pygmy-owls are
replaced by the least pygmy-owl (G.
minutissimum), Colima pygmy-owl (G.
palmarum), and the northern pygmyowl (G. gnoma) at higher elevations
(Schaldach 1963, p. 40; Howell and
Robbins 1995, pp. 19–20), mountains
with elevations as significant as those
separating the eastern and western
portions of the pygmy-owl’s distribution
in Mexico represent a significant
physical barrier, as discussed in the
Service’s DPS policy (61 FR 4725). The
eastern and western portions of the
current distribution of cactorum never
meet (Figure 1).
Recent evaluation of genetic
characteristics appears to indicate that
the eastern and western portions of the
pygmy-owl’s current distribution differ
from each other genetically (Proudfoot
et al. 2006b, pp. 7–9). As we have
discussed previously in this document,
this genetic differentiation may not be
adequate to define a subspecies, but it
does provide further evidence that the
eastern and western portions of the
pygmy-owl’s range are markedly
separate. There is genetic evidence that
the western group containing this
portion of the range does group closer
together than it does to owls in the
eastern portion of the overall range.
Proudfoot (2006a, p. 7) indicates that
pygmy-owls in this portion of the range
share no haplotypes with populations in
Texas or in the remainder of Mexico.
Additionally, in considering the work of
Proudfoot et al. (2006a and 2006b),
expert review concluded that, based on
evidence of restricted gene flow
between the Arizona/western Mexico
and Texas/eastern Mexico populations,
Arizona and Texas should be managed
as separate units and should be
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considered genetically distinct (Cicero
2008, p. 2; Oyler-McCance 2008, pp. 1–
2; Dumbacher 2008, p. 9), indicating
that Arizona and Texas, as portions of
the western and eastern distributions of
the pygmy-owl, contribute to the
respective genetic diversity of each of
these regions. Therefore, we find that
the eastern and western portions of the
range of Glaucidium brasilianum
cactorum are markedly separated from
each other as a consequence of physical
and ecological factors. As such, we
determine that the eastern and western
portions of the current distribution of
the pygmy-owl are discrete (Figure 4).
Significance
The Service’s DPS policy indicates
that one of the ways a DPS may be
significant to the taxon as a whole is if
the loss of the DPS would result in a
significant gap in the range of the taxon
(61 FR 4725). A gap in the range can be
interpreted as a physical gap, but may
also be considered to be a gap in the
continuous cline of genetic variation
found within the distribution of the
species. With regard to the pygmy-owl,
the western portion of the range
comprises approximately 68 percent of
the entire range of the taxon and,
consequently, the eastern portion of the
range represents approximately 32
percent of the range. Physically, the loss
of either of these geographic areas
represents a significant gap in the
distribution of the taxon. In addition,
Proudfoot et al. (2006a and 2006b)
indicate that the genetic characteristics
of the pygmy-owl may vary from Texas
to Arizona as a cline of variation based
on distance of separation. Loss of either
the western or eastern portion of this
cline represents a significant gap in the
distribution of genetic variation within
the overall pygmy-owl population.
Therefore, the loss of the current range
of the pygmy-owl as represented by the
western and eastern portions of the
current range, and the loss of a
substantial portion of the genetic
variation represented within the taxon
as a whole, would result in a significant
gap in the range of the pygmy-owl. As
such, we find that the eastern and
western population segments are
significant, based on evidence that loss
of the discrete population segment
would result in a significant gap in the
range of a taxon.
Determination for the Potential Western
DPS
Of the negative impacts we identified
in our 5-factor analysis above, the
following occur within western portions
of the pygmy-owl’s range: (1) Habitat
loss and fragmentation due to
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urbanization, improper grazing,
nonnative species invasions, fire,
agricultural development, and wood
cutting; (2) border issues; (3) inadequacy
of existing regulatory mechanisms; (4)
drought and climate change; (5)
predation; and (6) small population size.
Therefore, within the potential western
DPS configuration, impacts to pygmyowls and their habitat discussed under
factors A, C, and E may be affecting this
pygmy-owl population segment.
Despite the potential effects of these
impacts within the western portion of
the pygmy-owl’s range, low population
numbers, and apparent population
declines in local pygmy-owl
populations in the northern portion of
this population segment, the best
available scientific and commercial data
indicate that pygmy-owls remain
common in the majority of the western
portion of the pygmy-owl’s range.
Recent survey and monitoring in Sonora
indicated that the highest densities of
pygmy-owls occurred in the Sinaloan
deciduous forest of southern Sonora
(Flesch 2003, p. 42). During capture
efforts in 2008, AGFD (2008, p. 6)
documented multiple pygmy-owls
commonly responding at capture sites
in the thornscrub and tropical
deciduous forests of southern Sonora
and northern Sinaloa, an occurrence
which only rarely happened further
north in Sonoran desertscrub habitats.
While anecdotal, it appears that the
number and density of pygmy-owls is
higher in the thornscrub and deciduous
forest community types than in the
Sonoran Desert community type. This
occurrence and distribution agrees with
past conclusions found in the literature
(Hunter 1988, p. 7; Russell and Monson
1988, p. 141; Shaldach 1963, p. 40).
Because pygmy-owl habitat in the
southern portion of the western
population segment is primarily
thornscrub and dry tropical forests, it
logically follows that pygmy-owls are
more common in this portion of the
population segment. Based upon our
review of the best available commercial
and scientific data, we conclude that
pygmy-owl population numbers are not
being significantly affected by the
identified negative impacts in most of
the western portion of the pygmy-owl’s
range such that the population is in
danger of extinction or likely to become
so in the foreseeable future. Therefore,
we find that listing a western DPS of the
overall pygmy-owl population is not
warranted under the Act.
Determination for the Potential Eastern
DPS
Of the negative impacts we identified
in our 5-factor analysis above, the
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following occur within the eastern
portion of the pygmy-owl’s range: (1)
Habitat loss and fragmentation due to
urbanization, improper grazing,
nonnative species invasions, fire,
agricultural development, and wood
cutting; (2) loss or alteration of habitat
as a result of hurricanes; (3) lack of
adequate regulatory mechanisms; (4)
drought and climate change; (5)
predation; and (6) small population size.
Therefore, within the potential eastern
DPS configuration, impacts to pygmyowls and their habitat discussed under
factors A, C, E may be affecting this
pygmy-owl population segment.
The historical loss of pygmy-owl
habitat in the eastern portion of its range
has had significant effects on the
pygmy-owl. As discussed above, the
pygmy-owl was once a common
breeding species in Texas and
northeastern Mexico (Griscom and
Crosby 1926, p. 18; Friedmann et al.
1950, p. 145), but is now extirpated or
extremely rare in the area of the Rio
Grande Delta (Oberholser 1974, pp.
451–452). However, a disjunct
population generally occurring in the
area of Kenedy County, Texas, has been
estimated at 100 pygmy-owls (Tewes
1992, p. 24), 654 pairs (Wauer et al.
1993, p. 1074), and up to 1,823 pygmyowls (Mays 1996, p. 32). It should be
noted that these studies used different
methodologies and study areas, and are
not directly comparable, but do provide
estimates for the general area. A recent
concern about the populations in Texas
has been raised because of an apparent
decline in the number of pygmy-owl
nestlings banded in this population as
part of an ongoing nest box study in
Texas (Proudfoot 2010, p. 1). However,
comprehensive pygmy-owl surveys
throughout southern Texas have not
occurred for over a decade, and, without
a more comprehensive survey effort in
southern Texas, we cannot definitively
state that the overall population of
pygmy-owls in southern Texas matches
the decline of nestlings documented
during this nest box study. Pygmy-owls
may simply have moved to other areas
supporting suitable nesting habitat
(Proudfoot 2011b, p. 1).
While the literature indicates that
significant areas of pygmy-owl habitat
have been lost and fragmented
throughout the eastern portion of the
pygmy-owl’s range, there is no
indication that, where areas of suitable
habitat remain, numbers and densities
of pygmy-owls would not be similar to
those found in the same type of habitat
in Texas. Numbers of pygmy-owls in
Texas remain substantially higher than
those in the northwestern portion of the
pygmy-owl’s range, and similar to the
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apparently higher numbers found in the
southwestern portion of the range in
thornscrub and dry tropical forests.
Additionally, while urbanization and
agricultural development and
woodcutting may be ongoing negative
impacts in northeastern Mexico
(AQUASTAT 2007, p. 2; Cook et al.
2001, p. 4; Jahrsdoerfer and Leslie 1985,
p. 17; Tewes1993, pp. 28–29), the
occurrence of the majority of suitable
pygmy-owl habitat in Texas on private
ranches may reduce the potential for
these impacts to significantly affect
pygmy-owl populations in this area.
Wauer et al. (1993, p. 1076) state,
‘‘Changes in the ranch land habitats of
Kenedy and Brooks Counties have been
relatively limited, suggesting that
rancher landowners, at least in south
Texas, are being good land stewards.’’
At least currently, the Texas population
of pygmy-owls appears to be viable
(Wauer et al. 1993, p. 1071) and the
primary recruitment base for pygmy-owl
populations in this area (Wauer et al.
1993, p. 1076).
The best available scientific and
commercial information demonstrates
that, despite the ongoing negative
impacts to pygmy-owl habitat in the
eastern portion of its range, numbers
and densities have remained relatively
high. Therefore, we find that listing an
eastern DPS of the overall pygmy-owl
population is not warranted under the
Act.
Significant Portion of the Range
The Act defines ‘‘endangered species’’
as any species which is ‘‘in danger of
extinction throughout all or a significant
portion of its range,’’ and ‘‘threatened
species’’ as any species which is ‘‘likely
to become an endangered species within
the foreseeable future throughout all or
a significant portion of its range.’’ The
definition of ‘‘species’’ is also relevant
to this discussion. The Act defines the
term ‘‘species’’ as follows: ‘‘The term
‘species’ includes any subspecies of fish
or wildlife or plants, and any distinct
population segment [DPS] of any
species of vertebrate fish or wildlife
which interbreeds when mature.’’ The
phrase ‘‘significant portion of its range’’
(SPR) is not defined by the statute, and
we have never explicitly addressed it in
our implementing regulations either: (1)
The consequences of a determination
that a species is endangered or likely to
become so throughout a significant
portion of its range, but not throughout
all of its range; or (2) what qualifies a
portion of a range as ‘‘significant.’’
Two recent district court decisions
have addressed whether the SPR
language allows the Service to list or
protect less than all members of a
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defined ‘‘species’’: Defenders of Wildlife
v. Salazar, 729 F. Supp. 2d 1207 (D.
Mont. 2010), concerning the Service’s
delisting of the Northern Rocky
Mountain gray wolf (74 FR 15123; Apr.
12, 2009); and WildEarth Guardians v.
Salazar, 2010 U.S. Dist. LEXIS 105253
(D. Ariz. Sept. 30, 2010), concerning the
Service’s 2008 finding on a petition to
list the Gunnison’s prairie dog (73 FR
6660; Feb. 5, 2008). The Service had
asserted in both of these determinations
that it had authority under the Act to
protect only some members of a
‘‘species,’’ as that term is defined by the
Act (i.e., species, subspecies, or DPS).
Both courts ruled that the
determinations were arbitrary and
capricious on the grounds that this
approach violated the plain and
unambiguous language of the Act. The
courts concluded that reading the SPR
language to allow protecting only a
portion of a species’ range is
inconsistent with the Act’s definition of
‘‘species.’’ The courts concluded that,
once a determination is made that a
species (i.e., species, subspecies, or
DPS) meets the definition of
‘‘endangered species’’ or ‘‘threatened
species,’’ it must be placed on the list
in its entirety and the Act’s protections
applied consistently to all members of
that species (subject to modification of
protections through special rules under
sections 4(d) and 10(j) of the Act).
Consistent with that interpretation,
and for the purposes of this finding, we
interpret the phrase ‘‘significant portion
of its range’’ in the Act’s definitions of
‘‘endangered species’’ and ‘‘threatened
species’’ to provide an independent
basis for listing; thus there are two
situations (or factual bases) under which
a species would qualify for listing: A
species may be endangered or
threatened throughout all of its range
(which we have determined is not the
case with the pygmy-owl); or a species
may be endangered or threatened in
only a significant portion of its range. If
a species is in danger of extinction
throughout an SPR, the species is an
‘‘endangered species.’’ The same
analysis applies to ‘‘threatened species.’’
Based primarily on existing case law,
the consequence of finding that a
species is endangered or threatened in
only a significant portion of its range is
that the entire species shall be listed as
endangered or threatened, respectively,
and the Act’s protections shall be
applied across the species’ entire range.
We conclude, for the purposes of this
finding, that interpreting the SPR phrase
as providing an independent basis for
listing is the best interpretation of the
Act because it is consistent with the
purposes and the plain meaning of the
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key definitions of the Act. This
interpretation does not conflict with
established past agency practice (prior
to the 2007 Solicitor’s Opinion, which
interpreted language in section 4(c) as
limiting the application of ESA
protections to the significant portion of
a species’ range where it is endangered
or threatened, rather than throughout its
range) because no consistent, long-term
agency practice has been established,
and it is consistent with the most recent
judicial opinions that have most closely
examined this issue. Having concluded
that the phrase ‘‘significant portion of
its range’’ provides an independent
basis for listing and protecting the entire
species, we next turn to the meaning of
‘‘significant’’ to determine the threshold
for when such an independent basis for
listing exists.
Although there are potentially many
ways to determine whether a portion of
a species’ range is ‘‘significant,’’ we
conclude, for the purposes of this
finding, that the significance of the
portion of the range should be
determined based on its biological
contribution to the conservation of the
species. For this reason, we describe the
threshold for ‘‘significant’’ in terms of
an increase in the risk of extinction for
the species. We conclude that a
biologically-based definition of
‘‘significant’’ best conforms to the
purposes of the Act, is consistent with
judicial interpretations, and best
ensures species conservation. Thus, for
the purposes of this finding, a portion
of the range of the pygmy-owl is
‘‘significant’’ if its contribution to the
viability of the species is so important
that, without that portion, the pygmyowl would be in danger of extinction.
Therefore, if we determine that the
pygmy-owl is endangered or threatened
in a significant portion of its range, and
it would be in danger of extinction in
the rest of its range without that portion,
that portion is significant and we will
list the entire species according to its
status there.
We evaluate biological significance
based on the principles of conservation
biology using the concepts of
redundancy, resiliency, and
representation. Resiliency describes the
characteristics of a species that allow it
to recover from periodic disturbance.
Redundancy (having multiple
populations distributed across the
landscape) may be needed to provide a
margin of safety for the species to
withstand catastrophic events.
Representation (the range of variation
found in a species) ensures that the
species’ adaptive capabilities are
conserved. Redundancy, resiliency, and
representation are not independent of
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each other, and some characteristic of a
species or area may contribute to all
three. For example, distribution across a
wide variety of habitats is an indicator
of representation, but it may also
indicate a broad geographic distribution
contributing to redundancy (decreasing
the chance that any one event affects the
entire species), and the likelihood that
some habitat types are less susceptible
to certain threats, contributing to
resiliency (the ability of the species to
recover from disturbance). None of these
concepts is intended to be mutually
exclusive, and a portion of a species’
range may be determined to be
‘‘significant’’ due to its contributions
under any one of these concepts.
For the purposes of this finding, we
determine if a portion’s biological
contribution is so important that the
portion qualifies as ‘‘significant’’ by
asking whether, without that portion,
the representation, redundancy, or
resiliency of the species would be so
impaired that the species would have an
increased vulnerability to threats to the
point that the overall species would be
in danger of extinction (i.e., would be
‘‘endangered’’). Conversely, we would
not consider the portion of the range at
issue to be ‘‘significant’’ if there is
sufficient resiliency, redundancy, and
representation elsewhere in the species’
range that the species would not be in
danger of extinction throughout its
range if the population in that portion
of the range in question became
extirpated (extinct locally).
We recognize that this definition of
‘‘significant’’ establishes a threshold
that is relatively high. On the one hand,
given that the consequences of finding
a species to be endangered or threatened
in an SPR would be listing the species
throughout its entire range, it is
important to use a threshold for
‘‘significant’’ that is robust. It would not
be meaningful or appropriate to
establish a very low threshold whereby
a portion of the range can be considered
‘‘significant’’ even if only a negligible
increase in extinction risk would result
from its loss. Because nearly any portion
of a species’ range can be said to
contribute some increment to a species’
viability, use of such a low threshold
would require us to impose restrictions
and expend conservation resources
disproportionately to conservation
benefit; listing would be rangewide,
even if only a portion of the range of
minor conservation importance to the
species is imperiled. On the other hand,
it would be inappropriate to establish a
threshold for ‘‘significant’’ that is too
high. This would be the case if the
standard were, for example, that a
portion of the range can be considered
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‘‘significant’’ only if threats in that
portion result in the entire species being
currently endangered or threatened.
Such a high bar would not give the SPR
phrase independent meaning, as the
Ninth Circuit held in Defenders of
Wildlife v. Norton, 258 F.3d 1136 (9th
Cir. 2001).
The definition of ‘‘significant’’ used in
this finding carefully balances these
concerns. By setting a relatively high
threshold, we minimize the degree to
which restrictions will be imposed or
resources expended that do not
contribute substantially to species
conservation. But we have not set the
threshold so high that the phrase ‘‘in a
significant portion of its range’’ loses
independent meaning. Specifically, we
have not set the threshold as high as it
was under the interpretation presented
by the Service in the Defenders
litigation. Under that interpretation, the
portion of the range would have to be
so important that current imperilment
there would mean that the species
would be currently imperiled
everywhere. Under the definition of
‘‘significant’’ used in this finding, the
portion of the range need not rise to
such an exceptionally high level of
biological significance. (We recognize
that if the species is imperiled in a
portion that rises to that level of
biological significance, then we should
conclude that the species is in fact
imperiled throughout all of its range,
and that we would not need to rely on
the SPR language for such a listing.)
Rather, under this interpretation we ask
whether the species would be
endangered everywhere without that
portion, i.e., if that portion were
completely extirpated. In other words,
the portion of the range need not be so
important that even being in danger of
extinction in that portion would be
sufficient to cause the remainder of the
range to be endangered; rather, the
complete extirpation (in a hypothetical
future) of the species in that portion
would be required to cause the
remainder of the range to be
endangered.
The range of a species can
theoretically be divided into portions in
an infinite number of ways. However,
there is no purpose to analyzing
portions of the range that have no
reasonable potential to be significant
and threatened or endangered. To
identify only those portions that warrant
further consideration, we determine
whether there is substantial information
indicating that: (1) The portions may be
‘‘significant,’’ and (2) the species may be
in danger of extinction there or likely to
become so within the foreseeable future.
Depending on the biology of the species,
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its range, and the threats it faces, it
might be more efficient for us to address
the significance question first or the
status question first. Thus, if we
determine that a portion of the range is
not ‘‘significant,’’ we do not need to
determine whether the species is
endangered or threatened there; if we
determine that the species is not
endangered or threatened in a portion of
its range, we do not need to determine
if that portion is ‘‘significant.’’ In
practice, a key part of the portion status
analysis is whether the threats are
geographically concentrated in some
way. If the threats to the species are
essentially uniform throughout its
range, no portion is likely to warrant
further individual consideration.
Moreover, if any concentration of
threats applies only to portions of the
species’ range that clearly would not
meet the biologically-based definition of
‘‘significant,’’ such portions will not
warrant further consideration.
Therefore, having determined that the
pygmy-owl does not meet the definition
of a threatened or endangered species
throughout its range or within any
considered DPS configuration, we next
considered whether there are any
significant portions of the range where
the pygmy-owl is in danger of extinction
or is likely to become endangered in the
foreseeable future. We engaged in a
systematic process that began with
identifying any portions of the range of
the pygmy-owl that may warrant further
consideration.
To determine whether any portions of
the pygmy-owl’s range warranted
further consideration as possible
threatened or endangered significant
portions of the range, we reviewed the
entire supporting record for the status
review of this species with respect to
the geographic concentration of threats,
and the significance of portions of the
range to the conservation of the species.
We chose to first identify any portions
of the pygmy-owl’s range where the
species may be in danger of extinction
or likely to become so within the
foreseeable future. We found that
documented and potential population
declines are occurring in some parts of
the pygmy-owl’s range, but not
throughout the range of the pygmy-owl,
indicating the possibility that threats
affect the species to varying degrees
across the range of the pygmy-owl.
Additionally, the best available data
indicates that the impacts identified
above do not occur uniformly
throughout the range of the pygmy-owl.
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Analysis of Potential Significant
Portions of the Range
Pygmy-Owl Population Status Within
the Sonoran Desert Ecoregion
We identified one area of the pygmyowl’s range that warrants further
consideration as a possible threatened
or endangered significant portion of the
range. Based on our five-factor analysis
of threats throughout the range of the
pygmy-owl, we found that the Sonoran
Desert Ecoregion was an area where
documented and potential declines in
pygmy-owl populations have occurred,
indicating the species may be
threatened or endangered there.
Within the Arizona portion of the
Sonoran Desert Ecoregion, the pygmyowl occurs in very low numbers in
widely scattered population groups
within the State. Historically (i.e., late
1800s and early 1900s), pygmy-owls
occupied areas of south-central Arizona,
from New River, about 56 km (35 mi.)
north of Phoenix, south to the United
States and Mexico border, west to Agua
Caliente near Gila Bend and Cabeza
Prieta Tanks, and east to Tucson, and,
rarely, the San Pedro River (Bent 1938,
pp. 435–438; Monson and Phillips 1981,
pp. 71–72; Johnson et al. 2003, pp. 390–
391). The geographic area historically
occupied by pygmy-owls in Arizona
includes portions of Gila, Pima, Pinal,
Maricopa, Graham, Santa Cruz, Cochise,
Greenlee, and Yuma Counties.
Currently, the known locations of
pygmy-owls in Arizona are restricted to
two counties, Pima and Pinal (Service
2011, p. 1; Service 2009b, p. 1; Abbate
et al. 2000, pp. 15–16). The current
distribution of pygmy-owls within
Arizona is significantly reduced from its
historical distribution.
Historically, the pygmy-owl was
found as far north as New River in
Maricopa County, and, prior to the mid1900s, early naturalists considered the
pygmy-owl ‘‘not uncommon,’’ ‘‘of
common occurrence,’’ and a ‘‘fairly
numerous’’ resident of the areas in
which they traveled in Arizona
(Breninger 1898, p. 28; Gilman 1909, p.
148; Swarth 1914, p. 31). Recent data
indicate that there are fewer than 50
adult pygmy-owls and fewer than 10
nest sites in Arizona in any given year
(Abbate et al. 2000, pp. 15–16). Limited
surveys and monitoring conducted in
2009 indicate that pygmy-owls in
Arizona still occupy the areas of Avra
Valley, Altar Valley, and Organ Pipe
Cactus National Monument (Service
2009b, p. 1; 2011, p. 1). However,
populations of pygmy-owls in Arizona
are in an ongoing decline (AGFD 2008a,
p. 2). Comprehensive surveys have not
been conducted on the Tohono
O’odham Nation in Arizona. A number
of surveys have been completed on the
Nation with respect to various utility
and roadway projects, and some of these
surveys did document the presence of
pygmy-owl. But distribution of the data
from these surveys has been restricted
by the Nation and is not readily
available for analysis. There are large
areas of suitable habitat on the Nation,
but the information we have indicates
that pygmy-owls are patchily
distributed in those areas as in other
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Sonoran Desert Ecoregion SPR Analysis
We identified the Sonoran Desert
Ecoregion as a portion of the pygmyowl’s range that was potentially
significant, and that could potentially
meet the criteria for threatened or
endangered (Figure 3). The decision to
use this area to define the boundaries of
that portion of the overall pygmy-owl
range that may be significant was based
on factors related to pygmy-owl ecology
and information available related to the
status of the pygmy-owl. This portion of
the pygmy-owl’s range is characterized
by a generally unique vegetation
community. The Sonoran Desert has the
greatest diversity and vegetative growth
of any desert worldwide. It is the most
tropical of the three North American
warm deserts (Sonoran, Mojave, and
Chihuahuan) (Williams et al. 2001, pp.
1–2; MacMahon and Wagner 1985, pp.
105–202). The boundaries of this
vegetation community have been
consistently described in a number of
papers (Marshall et al. 2000, pp. 4–7;
McLaughlin and Bowers 1999, pp. 3–7;
Dimmitt 2000, pp. 13–15; Brown 1994,
p. 181; Leopold 1950, p. 513; Shreve
1951, pp. 1–3; and Nabhan and
Holdsworth 1998, pp. 1–5). Finally,
number and density estimates from
formal studies and incidental
observations from the field show that
this area has markedly lower numbers
and densities of pygmy-owls than the
other areas of its range, and that
population declines have occurred
within the area (AGFD 2008a, p. 2;
Flesch and Steidl 2006, p. 869).
For the purposes of this analysis, the
current range of the pygmy-owl within
the Sonoran Desert Ecoregion includes
those areas of the ecoregion within the
Arizona Counties of Pima and Pinal,
and the Mexican State of Sonora, from
the area immediately south of the
western border of Pima County, east to
Nogales, and south from Nogales to
Guaymas and then back northwest to
the western coast of Sonora.
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areas of the State and occur in similar
densities.
Within the Mexico portion of the
Sonoran Desert Ecoregion, pygmy-owl
numbers are higher, but, similar to their
distribution in Arizona, pygmy-owls
also occur here as scattered population
groups throughout the occupied area
(Flesch 2003, pp. 123–124). Recent
surveys and research in northwestern
Mexico indicate that numbers and
density of pygmy-owls are higher in
thornscrub and tropical deciduous
forest communities of southern Sonora
and Sinaloa than in the Sonoran
desertscrub and semi-desert grassland
vegetation communities of the Sonoran
Desert Ecoregion (Flesch 2003, pp. 39–
42; AGFD 2008a, p. 6). Long-term
monitoring of pygmy-owl sites in
northern Sonora indicates that the
extended drought has resulted in
reduced occupancy at monitored sites
(Flesch 2008, pp. 4–5). Pygmy-owl
survivorship is tied to precipitation
(Flesch 2008, pp. 5–6; Service 2004, p.
1). As in Arizona, drought has
negatively affected the numbers and
distribution of pygmy-owls on the
landscape within the analysis area
(Flesch 2008, pp. 5–6). While data
adequate to define population trends in
Sonora, Mexico, are lacking, field data
indicate that pygmy-owls in the
southern portions of the State (within
thornscrub and tropical deciduous
forests) are common and likely number
on the order of thousands, while further
north within the Sonoran Desert
Ecoregion, they are fewer in number,
more patchily distributed, and likely
number on the order of hundreds
(Flesch 2003, pp. 39–42; AGFD 2008a,
p. 6).
Significance of the Sonoran Desert
Ecoregion
This part of the pygmy-owl’s range
contains habitat that meet the needs of
the pygmy-owl for reproduction and
survival, and can support self-sustaining
population groups. It also provides a
mosaic of connected habitat maintaining
dispersal and genetic exchange among
subpopulations. The habitat found in
this portion of the range may become
increasingly important if the predictions
about climate change prove correct. As
hotter, drier conditions prevail, this
area, which already provides habitat
under these conditions, may provide the
largest, most contiguous blocks of
higher quality habitat if the wetter, more
tropical habitats (thornscrub and
tropical deciduous forests) are reduced
due to climate change. Conditions in the
Sonoran desert are also likely to become
hotter and drier. However, the
population groups of pygmy-owls found
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in the Sonoran Desert Ecoregion are
already adapted to the drier climate that
is likely to become more widespread
under current climate change scenarios
and, therefore, this shift in temperature
and precipitation may have a reduced
effect on pygmy-owls in this area.
Saguaros and other columnar cacti may
experience range-shifts associated with
climate change, however, there is much
uncertainty associated with the current
models of individual species responses
to climate change. Therefore,
predictions about the decline of
columnar cacti are too speculative to
consider in this finding. This
population group of pygmy-owls is
likely to become a more significant
contributor to the long-term viability of
this species.
Given the presumed adaptation of this
segment of the population to drier, more
extreme conditions, we considered
whether the demographic characteristics
of this population might be important
for the species to recover from predicted
changes in the ecosystem due to climate
change. Although birds in every
terrestrial habitat will be affected by
climate change, birds in arid lands show
lower overall vulnerability to the effects
of climate change (NABCI 2010).
Pygmy-owls in the Sonoran Desert
Ecoregion may be more likely to be able
to provide population support for the
remainder of its range. Therefore,
demographic characteristics and
population size within this portion of
the range might allow for at least partial
recovery of pygmy-owl populations
within this portion of the range
following disturbance events.
Pygmy-owls are secondary cavity
nesters, using cavities excavated in trees
and cacti. Within the Sonoran Desert
Ecoregion, pygmy-owls typically nest in
large, columnar cacti found throughout
the area. The Sonoran Desert Ecoregion
contains the greatest concentration of
large columnar cacti (saguaro, organ
pipe, hecho) anywhere in the range of
the pygmy-owl. While other areas to the
south of this portion of the range also
contain large, columnar cacti, they do
not occur in as high of densities, nor are
they as extensively distributed. In other
portions of its range, the pygmy-owl
nests in tree cavities; therefore, this
aspect of the pygmy-owl’s life history
requirements is not exclusive to
columnar cacti, but it is an important
and necessary element in this part of its
range because nesting in saguaros
reduces the impacts to eggs and
nestlings from the temperature extremes
and predation found in this portion of
the range.
There is some information indicating
that this subdivision of the western part
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of the range is different genetically than
the remainder of the range. Proudfoot
(2006a, p. 7) indicates that pygmy-owls
in this portion of the range share no
haplotypes with populations in Texas or
in the remainder of Mexico. Using
information in Proudfoot et al. (2006a,
pp. 6–9 and 2006b, pp. 5–7), we have
determined that the Arizona/Sonora
pygmy-owls contribute approximately
10 percent of the species total
mitochondrial DNA (mtDNA) variation
and 5 percent of the total alleles (gene
types) detected in their study (Service
2009c, p. 1). This data analysis indicates
that this part of the range does have
unique alleles and contributes to the
genetic variation within the range of the
pygmy-owl. There is evidence of
restricted gene flow between the
Arizona/western Mexico and Texas/
eastern Mexico populations (Cicero
2008, p. 2; Oyler-McCance 2008, pp. 1–
2; Dumbacher 2008, p. 9).
We have found that the Sonoran
Desert Ecoregion has unique habitat
characteristics and the pygmy-owls in
this area possess some unique
behavioral and genetic adaptations to
this area. Next, we evaluated whether,
should this portion of the range
theoretically be extirpated, the
remaining portion of the pygmy-owl’s
current range would be in danger of
extinction. This evaluation focused on
the pygmy-owl’s rangewide population
status and the importance of this part of
the range to the entire range.
There is general consensus in the
literature and other reports that pygmyowls remain common throughout most
of the areas of Mexico south of Sonora
and Texas. As noted above, the
population of pygmy-owls in this
ecoregion is small and scattered, and
thus represents only a small portion of
the overall pygmy-owl population. The
best available information does not
indicate that, under the theoretical
removal of the Sonoran Desert
Ecoregion from the current range of the
pygmy-owl, the remaining portion of the
range is likely to become extinct.
Therefore, we do not find the Sonoran
Desert Ecoregion of the pygmy-owl to be
significant, and thus it is not an SPR.
Sonoran Desert Ecoregion SPR Analyses
in Relation to the Eastern and Western
DPS’s
We determined that the eastern and
western portions of the pygmy-owl’s
current range represent DPSs; that is, we
found that they are discrete and
significant to the taxon as a whole (see
DPS discussion above). We found that
the best scientific and commercial
information did not indicate that the
negative impacts in these DPSs affect
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the pygmy-owl’s status such that these
DPSs warrant listing under the Act.
However, because we found that these
DPS configurations were appropriate
under our DPS policy, we next
evaluated whether the Sonoran Desert
Ecoregion represents significant
portions of the western and eastern
DPSs respectively.
Potential Sonoran Desert Ecoregion SPR
of the Western DPS
The portion of the Sonoran Desert
Ecoregion currently occupied by pygmyowls represents approximately 33
percent of the Western DPS (Figure 3).
Even though this is only approximately
one-third of the Western DPS, this
portion of the DPS may provide
important contributions to population
numbers, genetic diversity, and status of
the pygmy-owls within this DPS.
In considering the portion of the
western DPS outside of the Sonoran
Desert Ecoregion and whether it may be
in danger of extinction, we find it is
likely that the population of pygmyowls in this area is large enough to
withstand environmental catastrophes
and random perturbations. This is
because the area outside of the Sonoran
Desert Ecoregion represents
approximately 67 percent of the DPS,
and it likely supports a higher
proportion of the overall population
than the Sonoran Desert Ecoregion,
because this portion of the DPS is
characterized by thornscrub and tropical
deciduous forest communities, which
have been documented to support
higher numbers and densities of pygmyowls than Sonoran desertscrub
communities (Swarth 1914, p. 31;
Karalus and Eckert 1974, p. 218;
Monson and Phillips 1981, pp. 71–72;
Johnsgard 1988, Enriquez-Rocha et al.
1993, p. 158; Proudfoot 1996, p. 75;
Proudfoot and Johnson 2000, p. 5). The
production and population growth of
the pygmy-owls outside the Sonoran
Desert Ecoregion are likely high enough
to maintain viability of the population
under current conditions. Because the
Sonoran Desert Ecoregion occurs at the
northern end of the Western DPS, the
theoretical loss of that portion would
not result in fragmentation of the DPS
in a way that would affect movements
and connectivity of the pygmy-owl
population.
However, the theoretical loss of a
third of the range might represent a
significant loss of important habitat and
genetic diversity, affecting the
redundancy and representation of the
overall pygmy-owl population, and
possibly affect the remaining portion of
the population by reducing
metapopulation support including
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genetic adaptation and demographic
rescue. The current genetic structure of
the western DPS indicates that there is
population movement within the DPS
and, as a consequence, exchange of
genetic material among population
groups, even though the distribution of
pygmy-owls on the landscape is patchy.
Removal of approximately 33 percent of
the DPS might reduce the viability and
potential for long-term survival of the
remaining portion of the DPS. For
example, the Sonoran Desert Ecoregion
supports the portion of the DPS
population that is adapted to the unique
environment of the Sonoran Desert. Loss
of this segment of the population might
substantially decrease the genetic
diversity of the overall DPS to the point
that the pygmy-owl may not be able to
adapt to what may be the predominant
vegetation community under the
predicted effects of climate change.
However, the thornscrub and tropical
deciduous forest communities have
already been substantially reduced, and
this reduction and fragmentation is
likely to continue. Sonoran desertscrub
will likely expand to the north and
south as climates to the north become
warmer and climates to the south
become drier (Weiss and Overpeck
2005, p. 2074).
Pygmy-owl adaptations documented
in the Sonoran Desert Ecoregion include
the use of saguaro cavities as nest sites,
paler plumage coloration, ability to
obtain moisture from prey rather than
free-standing water, and the ability to
select nest locations that maintain
productivity during drought conditions
(AGFD 2008a, pp. 1–2 and b, pp. 3–7;
Flesch 2008, p. 3; Flesch and Steidl
2010, p. 1021). The ability of the
western DPS to adapt to impacts from
climate change may be substantially
reduced with the theoretical loss of the
Sonoran Desert Ecoregion.
The Sonoran Desert Ecoregion
population is characterized by lower
numbers and density of pygmy-owls.
This is likely the result of reduced
habitat quality and location of this
population group at the northern extent
of the Western DPS. While this
population may be considered marginal,
it is important to recognize that
marginal populations may have a high
adaptive significance to the species as a
whole, and marginal habitat
conservation, preservation and
management is one of the best ways to
conserve genetic diversity and resources
(Scudder 1989, p. 1). The portion of the
western DPS outside of the Sonoran
Desert Ecoregion may lack sufficient
resiliency to meet future environmental
changes that are already manifesting
themselves within this DPS. However,
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the pygmy-owl is somewhat of a habitat
generalist and, if impacts to habitat
occur over an extended period of time,
these populations may still be able to
adapt to environmental changes in this
DPS.
The primary vegetation communities
found outside of the Sonoran Desert
Ecoregion in the Western DPS,
thornscrub and subtropical dry forests,
are under significant stress. As
discussed above, thornscrub and
subtropical dry forests are among the
most threatened vegetation communities
in Mexico. Loss of dry tropical forest
occurs on as great, or greater, scale than
the loss of tropical rain forests (Trejo
and Dirzo 2000, p. 133). Only
approximately two percent of the
original distribution of subtropical dry
forests remains in Mesoamerica,
including Mexico. Some areas of intact
dry tropical forest remain on steep
slopes within the western DPS (Allnutt
2001, p. 3; Lugo 1999, p. 4). However,
the topography of such slopes, above
1,200 m (4,000), renders these areas
unsuitable for occupancy by pygmyowls. In areas occupied by pygmy-owls,
dry tropical forests are threatened by
woodcutting, clearing for agriculture,
urbanization, and impacts from invasive
species. Urbanization is increasing,
particularly in the southern portion of
the Western DPS (Lugo 1999, p. 2; Trejo
and Dirzo 2000, p. 133). In Mexico
specifically, only approximately 27
percent of the original cover of
seasonally dry forest remains intact
(Trejo and Dirzo 2000, p. 139).
In addition, increasing temperatures
due to climate change pose a serious
threat to subtropical dry forests due to
the transitional nature of the
community, and the narrow temperature
and precipitation requirements of many
of its native species (Allnutt 2001, p. 4).
Trejo and Dirzo (2000, p. 140) predicted
that, under current rates of
deforestation, by the year 2030, intact
seasonally dry forests would be reduced
to 10 percent of their original area.
Additionally, the remaining 10 percent
would likely be characterized by small,
vegetation islands separated from each
other, causing significant ecological
repercussions at the genetic, ecological,
and ecosystem function levels of the
ecoregion. Protected areas in Mexico
that include seasonally dry forests are
few and total less than 10 percent of the
remaining, intact forest areas in Mexico
(Trejo and Dirzo 2000, p. 140). This loss
and fragmentation of habitat, and the
influence of climate change on the
remaining areas of native habitat, may
substantially reduce the availability of
pygmy-owl habitat and, consequently,
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61893
pygmy-owl populations in the
foreseeable future.
We acknowledge that the Sonoran
Desert Ecoregion represents an
important portion of the Western DPS,
and of the taxon as a whole. However,
in order to find that the portion of the
western DPS in the Sonoran Desert
Ecoregion is significant under our SPR
policy, our position is that its
contribution to the viability of the
species must be so important that,
without that portion, the pygmy-owl
would be in danger of extinction. As
noted above in the discussion under
Sonoran Desert Ecoregion SPR Analysis,
even though pygmy-owls in this area
possess some unique behavioral and
genetic adaptations, the population of
pygmy-owls in this ecoregion is small
and scattered, and thus represents only
a small portion of the overall pygmyowl population. The best available
information does not indicate that, if the
Sonoran Desert Ecoregion portion of the
pygmy-owl’s range is extirpated, the
remaining portion of the Western DPS is
likely to become extinct. Therefore, we
do not find the Sonoran Desert
Ecoregion of the pygmy-owl to be
significant, and thus it is not an SPR.
SPR Conclusion
In summary, we have thoroughly
analyzed all potentially-listable entities
of the pygmy-owl. For the reasons
described above, we find that the
pygmy-owl is not in danger of
extinction now, nor is it likely to
become endangered within the
foreseeable future, throughout all or any
significant portion of its range.
Therefore, listing the pygmy-owl as
endangered or threatened under the Act
is not warranted at this time.
We request that you submit any new
information concerning the status of, or
threats to, the pygmy-owl to our Arizona
Ecological Services Office (see
ADDRESSES) whenever it becomes
available. New information will help us
monitor the pygmy-owl and encourage
management of this subspecies and its
habitat. If an emergency situation
develops for the pygmy-owl or any other
species, we will act to provide
immediate protection.
References Cited
A complete list of all references cited
in this document is available on the
Internet at https://www.regulations.gov
and upon request from the Arizona
Ecological Services Office (see
ADDRESSES).
Authors
The primary authors of this notice are
the staff members of the Arizona
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Ecological Services Office (see FOR
FURTHER INFORMATION CONTACT).
Authority
The authority for this action is section
4 of the Endangered Species Act of
1973, as amended (16 U.S.C. 1531 et
seq.).
Dated: September 27, 2011.
Rowan W. Gould,
Acting Director, U.S. Fish and Wildlife
Service.
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Agencies
[Federal Register Volume 76, Number 193 (Wednesday, October 5, 2011)]
[Proposed Rules]
[Pages 61856-61894]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-25565]
[[Page 61855]]
Vol. 76
Wednesday,
No. 193
October 5, 2011
Part IV
Department of the Interior
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Fish and Wildlife Service
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50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a
Petition To List the Cactus Ferruginous Pygmy-Owl as Threatened or
Endangered With Critical Habitat; Proposed Rule
Federal Register / Vol. 76 , No. 193 / Wednesday, October 5, 2011 /
Proposed Rules
[[Page 61856]]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[FWS-R2-ES-2011-0086; MO 92210-0-0008]
Endangered and Threatened Wildlife and Plants; 12-Month Finding
on a Petition To List the Cactus Ferruginous Pygmy-Owl as Threatened or
Endangered With Critical Habitat
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
-----------------------------------------------------------------------
SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
12-month finding on a petition to list the cactus ferruginous pygmy-owl
(Glaucidium brasilianum cactorum) as threatened or endangered and to
designate critical habitat under the Endangered Species Act of 1973, as
amended (Act). Additionally, the petition requested that we recognize
and list a western subspecies of the cactus ferruginous pygmy-owl
(Glaucidium ridgwayi cactorum), or, alternatively, two potential
distinct population segment (DPS) configurations. After review of all
available scientific and commercial information, we find that
Glaucidium ridgwayi cactorum is not a valid taxon, and, therefore, not
a listable entity under the Act. Additionally, using the currently
accepted taxonomic classification of the pygmy-owl (Glaucidium
brasilianum cactorum), we find that listing the pygmy-owl is not
warranted at this time throughout all or a significant portion of its
range, including the petitioned and other potential DPS configurations.
However, we ask the public to submit to us at any time any new
information concerning the taxonomy or status of the pygmy-owl, as well
as any new information on the threats to the pygmy-owl or its habitat.
DATES: The finding announced in this document was made on October 5,
2011.
ADDRESSES: This finding is available on the Internet at https://www.regulations.gov at Docket Number FWS-R2-ES-2011-0086. Supporting
documentation we used in preparing this finding is available for public
inspection, by appointment, during normal business hours at the U.S.
Fish and Wildlife Service, Arizona Ecological Services Office, 2321
West Royal Palm Road, Suite 103, Phoenix, AZ 85021-4951. Please submit
any new information, materials, comments, or questions regarding this
finding to the above address.
FOR FURTHER INFORMATION CONTACT: Steve Spangle, Field Supervisor,
Arizona Ecological Services Office (see ADDRESSES); telephone 602-242-
0210; or by facsimile 602-242-2513. If you use a telecommunications
device for the deaf (TDD), please call the Federal Information Relay
Service (FIRS) at 800-877-8339.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Endangered Species Act (Act) (16 U.S.C.
1531 et seq.) requires that, for any petition to revise the Federal
Lists of Endangered and Threatened Wildlife and Plants that contains
substantial scientific and commercial information that listing a
species may be warranted, we make a finding within 12 months of the
date of receipt of the petition. In this finding, we determine whether
the petitioned action is: (1) Not warranted, (2) warranted, or (3)
warranted, but immediate proposal of a regulation implementing the
petitioned action is precluded by other pending proposals to determine
whether species are threatened or endangered, and expeditious progress
is being made to add or remove qualified species from the Lists of
Endangered and Threatened Wildlife and Plants. Section 4(b)(3)(C) of
the Act requires that we treat a petition for which the requested
action is found to be warranted but precluded as though resubmitted
annually on the date of such finding. Therefore, a new finding is to be
made within 12 months and subsequently thereafter until we take action
on a proposal to list or withdraw our original finding. We must publish
these 12-month findings in the Federal Register.
Previous Federal Actions
On March 20, 2007, we received a petition dated March 15, 2007,
from the Center for Biological Diversity and Defenders of Wildlife
(petitioners) requesting that we list the cactus ferruginous pygmy-owl
(Glaucidium brasilianum cactorum) (pygmy-owl) as a threatened or
endangered species under the Endangered Species Act (Act) (CBD and DOW
2007). Additionally, the petition requested the designation of critical
habitat concurrent with listing. The petition clearly identified itself
as a petition and included the identification information, as required
in 50 CFR 424.14(a). We acknowledged the receipt of the petition in a
letter to the petitioners dated June 25, 2007, stating that we were
proceeding with a review of the petition.
The petitioners described three potentially listable entities of
the pygmy-owl: (1) An Arizona distinct population segment (DPS) of the
pygmy-owl; (2) a Sonoran Desert DPS of the pygmy-owl; and (3) the
western subspecies of the pygmy-owl, which they identified as
Glaucidium ridgwayi cactorum. As an immediate action, the petitioners
requested that we promulgate an emergency listing rule for the pygmy-
owl. In our June 25, 2007, response letter to the petitioners, we
described our evaluation of the need for emergency listing and stated
our determination that emergency listing was not warranted for the
pygmy-owl. We also stated that the designation of critical habitat
would be considered if listing of the pygmy-owl was found to be
warranted.
In the Federal Register of June 2, 2008 (73 FR 31418), we published
a 90-day finding in which we determined that the petition presented
substantial scientific and commercial information to indicate that
listing the pygmy-owl may be warranted. A more thorough summary of
previous Federal actions related to the pygmy-owl can be found in the
June 2, 2008 90-day finding (73 FR 31418).
Following the publication of our 90-day finding on this petition,
we initiated a status review to determine if listing of the pygmy-owl
was warranted. During our status review, we solicited and received
information from the general public and other interested parties on the
status of the pygmy-owl. We consulted with experts, agencies,
countries, and tribes to gather pertinent information, and ensure that
experts and affected parties were aware of the status review and of the
opportunity to provide input. We identified, contacted, and consulted
with a diverse group of experts and interested persons in an effort to
ensure that we gathered and evaluated the best available scientific and
commercial information on this subspecies to inform our 12-month
finding.
On December 12, 2009, we received a 60-day Notice of Intent to Sue
from the petitioners for failure to produce a timely 12-month finding
on their petition. They subsequently filed suit on February 17, 2010,
in the U.S. District Court for the District of Arizona. That complaint
was subsequently consolidated in the U.S. District Court for the
District of Columbia along with another case filed by the Center for
Biological Diversity and thirteen cases filed by Wild Earth Guardians,
all related to petition finding deadlines. The court in the
consolidated case
[[Page 61857]]
approved two settlement agreements between the parties on September 9,
2011. In re Endangered Species Act Deadline Litigation, Misc. Action
No. 10-377 (EGS), MDL Docket No. 2165 (D.D.C. Sept. 9, 2011) (Docs. 55
& 56). The settlement agreements stipulate that the Service will submit
to the Federal Register a proposed listing rule or a not warranted
finding for the cactus ferruginous pygmy-owl no later than the end of
Fiscal Year 2011, which is September 30, 2011.
This notice constitutes a 12-month finding for the petition to list
the pygmy-owl as threatened or endangered. We base our finding on a
review of the best scientific and commercial information available,
including all substantive information received during our status
review.
In this finding, we first provide background information on the
biology of the pygmy-owl. Included in this background is our analysis
of the petitioner's request that we recognize a western subspecies of
the pygmy-owl (Glaucidum ridgwayi cactorum), which represents a
proposed change in the taxonomic classification of the pygmy-owl. Then,
we consider each of the five factors listed in section 4(a)(1) of the
Act. For each factor, we first determine whether any negative impacts
appear to be affecting the pygmy-owl anywhere in the subspecies' range,
and whether any of these impacts rise to the level of threats such that
the pygmy-owl is endangered or threatened throughout its range,
according to the statutory standard.
After the rangewide assessment, we evaluate the validity of the
petitioned distinct population segments (DPSs), as well as other
potential DPS configurations suggested by information submitted during
the status review or by the ecology, occurrence, and distribution of
the pygmy-owl. This analysis determines whether any of the DPS
configurations meet the criteria for discreteness and significance
under our DPS policy (see Distinct Vertebrate Population Segment
section below). We then evaluate whether there is a significant portion
of the pygmy-owl's range that warrants further evaluation, consistent
with the Act's definitions for ``endangered species'' and ``threatened
species,'' which requires analysis of whether a ``species'' is
endangered or threatened within ``a significant portion of its range''
(see Significant Portion of the Range section below). Finally, we make
our finding with regard to the petitioned action and our evaluation as
described above.
Species Information
Description
The pygmy-owl is in the order Strigiformes and the family
Strigidae. It is a small bird, approximately 17 centimeters (cm) (6.75
inches (in)) long. Generally, male pygmy-owls average 58 grams (g) to
66 g (2.0 to 2.3 ounces (oz)) and females average 70 g to 75 g (2.4 to
2.6 oz) (AGFD 2008b, p. 3; Proudfoot and Johnson 2000, p. 16; Johnsgard
1988, p. 159). The pygmy-owl is reddish brown overall, with a cream-
colored belly streaked with reddish brown. Color may vary, with some
individuals being more grayish brown (Proudfoot and Johnson 2000, pp.
15-16). The crown is lightly streaked, and a pair of dark brown or
black spots outlined in white occurs on the nape, suggesting ``eyes,''
leading to the name ``Cuatro Ojos'' (four eyes), as it is sometimes
called in Mexico (Oberholser 1974, p. 451). The species lacks ear
tufts, and the eyes are yellow. The tail is relatively long for an owl
and is reddish brown in color, with darker brown bars. Pygmy-owls have
large feet and talons relative to their body size.
Taxonomy
The petitioners requested that we recognize a change in the
taxonomic classification of the pygmy-owl (CBD and DOW 2007, pp. 1-2).
In considering taxonomic data, the Service relies ``on standard
taxonomic distinctions and the biological expertise of the Department
and the scientific community concerning the relevant taxonomic group''
(50 CFR 424.11(a)) and on ``the best available scientific and
commercial information'' (50 CFR 424.11(b)). The use of specific
taxonomic data is at the discretion of the Service, as long as the
information is reliable and meets the above standards. With regard to
the pygmy-owl, existing avian checklists attempt to present the most
current taxonomic classifications, but discrepancies among checklists
demonstrate that there is scientific debate and disagreement over some
accepted taxonomic designations. Taxonomic changes within these
checklists generally occur as a result of a proposal to change the
existing taxonomy. Lack of reference to a proposed taxonomic change
within these checklists cannot be interpreted as rejection (or
acceptance) of a proposed change. It may simply mean a proposal has not
been submitted or evaluated. Absolute reliance on one or more of these
avian checklists, absent consideration of recent studies, would be
arbitrary on the part of the Service. The Service has the
responsibility for deciding what taxonomic entities are to be protected
under the Act, based on the best available scientific information. We
address any conflicting information or conflicting expert opinion by
carefully evaluating the underlying scientific information and weighing
its reliability and adequacy according to the considerations of the Act
and our associated policies and procedures.
When we previously listed the pygmy-owl as endangered in 1997 (62
FR 10730; March 10, 1997), and in all subsequent regulatory and legal
actions, we followed the currently accepted taxonomic classification,
Glaucidium brasilianum cactorum. We considered G. b. cactorum to occur
from lowland central Arizona south through western Mexico to the
Mexican states of Colima and Michoac[aacute]n, and from southern Texas
south through the Mexican states of Tamaulipas and Nuevo Leon,
consistent with most of the contemporary literature (Johnsgard 1988, p.
159; Millsap and Johnson 1988, p. 137; Oberholser 1974, p. 452;
Friedmann et al. 1950, p. 145), and the last American Ornithologist
Union (AOU) list that addressed avian classification to the subspecies
level (AOU 1957) (Figure 1). The AOU checklist is generally accepted as
the primary authority for avian taxonomic classification, and the 1957
AOU checklist description is the currently accepted taxonomic
classification of the pygmy-owl at the subspecies level.
[[Page 61858]]
[GRAPHIC] [TIFF OMITTED] TP05OC11.003
The petitioners requested a revised taxonomic consideration for the
pygmy-owl based on Proudfoot et al. (2006a, p. 9; 2006b, p. 946) and
K[ouml]nig et al. (1999, pp. 160, 370-373), classifying the northern
portion of Glaucidium brasilianum's range as an entirely separate
species, G. ridgwayi, and recognizing two subspecies of G. ridgwayi--G.
r. cactorum in western Mexico and Arizona and G. r. ridgwayi in eastern
Mexico and Texas (Figure 1). Other recent studies proposing or
supporting the change to G. ridgwayi for the northern portion of G.
brasilianum's range have been published in the past 15 years (Heidrich
et al. 1995, p. 2, 25; Navarro-Siguenza and Peterson 2004, p. 5).
Groups classified within species, such as subspecies, are important
in the discussion of biodiversity because they represent the
evolutionary potential within a species. Recognizing this, a number of
existing lists of threatened, endangered, or special status species
include subspecific groups (Haig et al. 2006, p. 1585). We considered
the information in these existing lists and other literature as we
evaluated the petitioned taxonomic classification. The 1957 AOU
checklist is the last AOU checklist that described subspecies.
Subsequent AOU checklists have limited their descriptions to the
species level only and are, therefore, not helpful in our evaluation.
In our 90-day finding for this petition (73 FR 31418), we indicated
that the petition presented reliable and substantive information that a
taxonomic revision may be warranted. The suggested taxonomic change is
based on recently published recommendations (Proudfoot et al. 2006a, p.
9; 2006b, p. 946; K[ouml]nig et al. 1999, pp. 160, 370-373) to revise
pygmy-owl taxonomy. Various other publications also provide evidence
that the taxonomic status of the pygmy-owl has not been resolved
(Proudfoot and Johnson 2000, pp. 4-5; K[ouml]nig et al. 1999, p. 373;
Phillips 1966, p. 93; Buchanan 1964, p. 107). Information received
during our status review also indicates that pygmy-owl taxonomy needs
additional work to resolve current questions (Johnson and Carothers
2008b, pp. 5-6; Robbins 2008, p. 1; Voelker 2008, p. 1).
Taxonomic nomenclature for the pygmy-owl has changed over time.
Originally called Glaucidium ferrugineum in 1872 by Coues (Coues 1872,
p. 370), the pygmy-owl has also been known as G. ferrugineus (Aiken
1937, p. 29) and G. phalo(a)enoides (Fisher 1893, p. 199; Gilman 1909,
p. 115, Swarth 1914, p. 31; Kimball 1921, p. 57). Since the 1920's, the
pygmy-owl has been classified as G. brasilianum (van Rossem 1937, p.
27; Bent 1938, p. 435; Peters 1940, p. 130; Brandt 1951, p. 653; Sutton
1951, p. 168). We will focus our discussion at the subspecies level
since the petitioned entity is at the subspecies level of
classification. As such, we will not evaluate or discuss whether the
appropriate species classification is G. brasilianum or G. ridgwayi.
The petitioners asked the Service to recognize a subspecies,
Glaucidium ridgwayi cactorum, described by
[[Page 61859]]
Proudfoot et al. (2006a, pp. 9-10; 2006b, p. 2, 9) as the listable
entity in the petition. The primary difference between the petitioned
subspecies and the currently accepted description of G. brasilianum
cactorum is the latter's more extensive distribution to the south and
east (Figure 1). The range of the G. b. cactorum subspecies we
originally listed in 1997 is Arizona, northwestern Mexico, the Lower
Rio Grande Valley of Texas, and northeastern Mexico, for a general
distribution that runs from central Mexico northward on both sides of
the Sierra Madre mountains into Arizona and Texas. The range of the
proposed G. r. cactorum does not extend as far south as G. b. cactorum.
The two G. ridgwayi subspecies proposed by the petition encompass the
northwestern (G. r. cactorum) and northeastern (G. r. ridgwayi)
extensions of the range of G. b. cactorum. Specifically, the petition
describes the range of the suggested subspecies, G. r. cactorum, as
extending from Arizona on the north through the States of Sonora and
Sinaloa in Mexico (Figure 2).
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Our analysis of whether to accept the petitioners' proposed
Glaucidium ridgwayi cactorum subspecies as a listable entity includes
an evaluation of whether there are historical or current descriptions
or studies of the proposed subspecies that would support the
description of the petitioned subspecies based on Proudfoot et al.
(2006a, 2006b). A number of subspecies of G. brasilianum have been
described or suggested (Proudfoot and Johnson 2000, p. 4; Friedmann et
al. 1950, pp. 145-147), including various descriptions of a cactorum
subspecies, the distribution of some of which generally match the
petitioned subspecies. Therefore, the delineation of a cactorum
subspecies as petitioned is not a new classification, but one that has
been described previously in the literature under G. brasilianum.
With regard to existing literature, van Rossem (1937, pp. 27-28)
described the earliest cactorum subspecies that approximates the
distribution of the petitioned subspecies. This was a newly described
subspecies of ferruginous pygmy-owl and was described from a ``giant
cactus grove between Empalme and Guaymas * * * Sonora, Mexico'' (van
Rossem 1937, p. 27). Van Rossem restricted this new subspecies to
northwestern Mexico and Arizona (Figure 3). Van Rossem also included a
more southern and eastern subspecies, ridgwayi, that was described as
occurring in southern Mexico and central America, but also Texas (van
Rossem, 1937, pp. 27-28). He specifically excluded the Texas population
from cactorum, about which
[[Page 61860]]
he wrote ``they approximate very closely the measurements and tail
characters of cactorum * * * in color they are best referred to
ridgwayi'' (van Rossem 1937, pp. 27-28; italics added). The 1944 AOU
checklist accepted this classification and described its distribution
as southern Arizona to Nayarit, in western Mexico (AOU 1944, p. 50)
(Fig. 3). However, in a later publication van Rossem (1945, p. 111)
indicated that cactorum extended only to the Sonora and Sinaloa border
in Mexico (Figure 3), perhaps excluding Nayarit, because his 1937
publication indicates that the specimen from Nayarit was not typical
(van Rossem 1937, p. 28). Karalus and Eckert (1971, p. 223) give a
southern distribution for cactorum of western and northwestern Sonora
(Figure 3). Proudfoot et al. (2006a, p. 9; 2006b, p. 7) indicate the
state of Sinaloa is the southern extent of the range, while K[ouml]nig
et al. (1999, p. 373) extend the distribution of cactorum into Nayarit
and Jalisco in western Mexico (Figure 3). Freethy (1992, p. 121) simply
states that western Mexico is the southern limit of cactorum. Clements
(2007, p. 171) recognizes the cactorum subspecies, but gives no
distribution.
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The chronology described in the previous paragraph, which excludes
the currently accepted distribution of Glaucidium brasilianum cactorum,
focuses on descriptions in the literature which generally approximate
the petitioned description of G. ridgwayi cactorum, and there is
consensus that cactorum extended northward into Arizona. However, it is
evident there is inconsistency regarding the southern extent of the
subspecies. With the exception of van Rossem (1937, pp. 27-28), who
uses morphological characteristics to describe the subspecies, most of
the above descriptions of the cactorum subspecies do not indicate why
they have ascribed the subspecies to the ranges indicated in these
publications. K[ouml]nig et al. (1999, p. 373) simply uses the
morphological characters of van Rossem (1937, pp. 27-28). K[ouml]nig et
al. (1999, entire) and Proudfoot et al. (2006a; 2006b, entire) do
classify cactorum using genetic data, but draw different conclusions
with regard to the southern boundary. The incremental southward
extension of the various cactorum ranges may provide some support for
the idea of a clinal pattern of differentiation in which genetic and
morphological differences occur in an incremental manner, as opposed to
more abrupt changes that are more likely to represent a boundary
between two distinct subspecies groupings. The data presented in the
petition (Proudfoot et al. 2006a; 2006b, entire) are not sufficient to
clarify the groupings in the literature, nor does it allow us to
determine if the subspecies ranges are distinct because there is a lack
of adequate sampling in southern and eastern Mexico. The uncertainty of
the southern boundary would suggest that additional sampling is needed
to refine this portion of the range of cactorum. In the presence of
unresolved inconsistencies, the Service relies upon the ``standard
taxonomic distinctions (50 CFR 424.11(a)); in this case, the currently
accepted taxonomic classification (AOU 1957).
In addition to reviewing historical and current descriptions of the
subspecies, we requested review and input on the issue of taxonomic
classification of the petitioned entity from 10 individuals with
biological expertise and background in this issue. Of the 10 we
consulted, 5 provided comments on specific questions we asked regarding
the issues of taxonomic classification, genetic differentiation, and
genetic diversity based on recent and historical studies and
publications related to pygmy-owl taxonomic classification. Information
submitted by all five experts indicated that, while there are certain
aspects of the information presented in the petition that support
acceptance of the petitioned entity, there is insufficient information
regarding how to define a distinct subspecies. Additional work is
needed to clarify the distribution of the subspecies, especially in
regards to the southern boundary (Voelker 2008, p. 1; Cicero 2008, p.
2; Robbins 2008, p. 1; Oyler-McCance 2008, pp. 1-2; Dumbacher 2008, pp.
2-8). A summary of their comments is presented below.
Dumbacher (2008, p. 7) provided a summary of considerations in
response to our request for input on this issue: ``In summary,
Proudfoot et al. 2006a and 2006b do not provide a critical test for the
subspecies Glaucidium ridgwayi ridgwayi or G.r. cactorum or their
geographical ranges. The data are consistent with current subspecies
names in that they show: (1) Isolation by distance across the range,
albeit with larger genetic breaks in the region that corresponds with
the subspecies names [as described by van Rossem 1937]; (2) and
significant variation among major geographical areas that broadly
correspond to present subspecies names [van Rossem 1937]. However, it
is not clear: (1) Where exactly the subspecies boundaries occur; (2)
whether the boundary will be geographically distinct or correspond to
characters used in the original subspecies designation, such that the
two groups would qualify for subspecies under the 75 percent rule [75
percent of individuals in a new subspecies (or region) are diagnosably
different from the other possible subspecies]; or (3) whether a broad
hybrid zone or cline would be discovered that might call the two
subspecies into question. Further data are needed to critically test
the validity of the subspecies and to identify the most appropriate
geographic boundary between them. Proudfoot et al. (2006b) make a plea
for more data in critical areas, such as between Sonora and Sinaloa,
and I would argue further south as well.''
Cicero (2008, p. 2) adds, ``On the basis of these data, I would
argue that Arizona and Texas populations should be managed as separate
units. However, further study of the variation in morphology and
plumage (the characters originally used to describe cactorum) is needed
before we can reliably apply names to these populations. Thus, in my
opinion, the molecular data provided by Proudfoot et al. (2006a and
2006b) do not clarify subspecific limits and ranges in North American
populations of G. brasilianum''. Similarly, Oyler-McCance (2008, p. 2)
indicates that, ``within the United States, it is clear that the
Arizona group is much different from the Texas group and should not be
considered as one group. What is less clear, however, is where exactly
to draw the boundary between the two subspecies * * *. It would be
informative to look at other characteristics (morphology, behavior,
geographic distribution) and see how well they fit with the patterns
provided by the genetic data. Only then, using all those
characteristics, would it be prudent to make a decision.''
Robbins (2008, p. 1) indicated that work on a molecular-based
phylogeny of New World pygmy-owls is about to be completed that will
inform this issue. He suggested that acceptance of the petitioned
entity be delayed until this work has been published. However, the
study to which Robbins refers will focus on species-level analyses, and
it may not provide additional information regarding the distribution of
subspecies and, as of the date of this finding, has not yet been
published.
Recently, the Committee on Classification and Nomenclature on North
and Middle American birds (the Checklist Committee) of the AOU
considered a proposal to separate Glaucidium brasilianum ridgwayi as a
distinct species, but rejected that proposal, citing the need to wait
for additional work (AOU 2009).
In fairness to Proudfoot and his collaborators, their two 2006
studies are more general in nature and did not have the objective of
defining pygmy-owl classification to the subspecies level. In addition,
Proudfoot and his fellow authors, similar to the authors of many other
publications related to pygmy-owl taxonomy, pointed out the need for
additional work to clarify the taxonomic classification of pygmy-owls.
Therefore, when we consider the recent information provided by
Proudfoot et al. (2006a; 2006b, entire) and K[ouml]nig et al. (1999,
entire), in combination with the historical descriptions of
distributions for the subspecies cactorum, there is evidence of a
general nature that the petitioned subspecies may have merit. However,
after reviewing the best available information, we find that
uncertainty and inconsistency exists with regard to the delineation of
the range of these subspecies.
The peer reviewers who provided information to the Service
regarding this issue represent respected experts with considerable
knowledge of the current science regarding avian taxonomy and
classification. They point out that a combination of factors, including
morphological, vocal, and genetic, need to be considered in greater
depth, with
[[Page 61862]]
additional sampling, to determine if the petitioned taxonomic
classification should be accepted, and we are in agreement with these
comments. Given the uncertainty and lack of clarification found in the
best available scientific and commercial information, we rely on the
``biological expertise of the Department and the scientific community
concerning the relevant taxonomic group'' (50 CFR 424.11(a)).
In summary, we find that there is considerable uncertainty as to
whether the genetic differentiation found at the far ends of the pygmy-
owl's distribution represented by Arizona and Texas are adequate to
define the eastern and western distributions as separate subspecies.
These differences may simply represent isolation by distance with a
clinal gradation of genetic differentiation between the two extremes of
the range, which would be inconsistent with the existence of two
different subspecies. Therefore, the best available scientific and
commercial information does not suggest that genetic differentiation
reported by Proudfoot et al. (2006a; 2006b, entire) and K[ouml]nig et
al. (1999, entire) supports their proposed Glaucidium ridgwayi cactorum
subspecies classification at this time. Future work and studies may
clarify and resolve these issues, but, in the meantime, we will
continue to use the currently accepted distribution of G. brasilianum
cactorum as described in the 1957 AOU checklist and various other
publications (Johnsgard 1988, p. 159; Millsap and Johnson 1988, p. 137;
Oberholser 1974, p. 452; Friedmann et al. 1950, p. 145). The Service
accepted this information under the previous listing of the pygmy-owl
(62 FR 10730). We, therefore, reject the petitioned listing of a
western subspecies of pygmy-owl, G. r. cactorum, as an insufficiently
supported taxonomic subspecies at this time.
The following discussion will examine the potentially listable
entities of Glaucidium brasilianum cactorum, the currently recognized
subspecies of pygmy-owl.
Distribution and Status
The currently accepted distribution of the pygmy-owl is described
as south central Arizona and southern Texas in the United States, south
through the Mexican States of Sonora, Sinaloa, Nayarit, Jalisco,
Colima, and Michoac[aacute]n on the west and Nuevo Leon and Tamaulipas
on the east (Figure 1). Available information on the specific
distribution of the pygmy-owl within this general area is not
comprehensive, especially in the southern portions of Mexico. As
described below, we have relatively detailed information on pygmy-owl
distribution in the United States and Sonora, Mexico. The following is
a description of the available information we have related to the
distribution of the pygmy-owl.
The cactus ferruginous pygmy-owl is the northernmost subspecies of
the ferruginous pygmy-owl. This subspecies was originally described as
being common in the lower Rio Grande River in southern Texas
(Oberholser 1974, p. 452) and along the Salt and Gila Rivers in central
Arizona (Fisher 1893, p. 199; Breninger 1898, p. 128; Gilman 1909, p.
148). In Arizona and Texas, apparent range and population declines have
occurred, reducing the current distribution of the pygmy-owl in these
areas (Oberholser 1974, p. 452; Monson and Phillips 1981, p. 72;
Proudfoot and Johnson 2000, p. 3). Historical records for the pygmy-owl
in Arizona span at least five counties in southern and south-central
Arizona, including Maricopa, Pima, Pinal, Santa Cruz and Yuma Counties
(Johnson et al. 2003, p. 394). Most of the historical (pre-1900) and
recent (post-1990) records are from Pima County. Between 1872 and 1971,
a total of 56 published records or specimens were recorded for Arizona.
Of those, almost half (27) were from Pima County (Johnson et al. 2003,
pp. 392-395). Although the pygmy-owl was historically recorded
primarily from lowland riparian habitats, all recent records are from
upland and xeroriparian (vegetation community in drainages associated
with seasonal or intermittent water) Sonoran desertscrub (Abbate et al.
2000, pp. 15-16, Service 2009b, p. 1: 2011, p. 1).
Some information provided by the public suggested that the pygmy-
owl is an obligate wet riparian species in south-central Arizona and a
preferential wet riparian species in southern Arizona, tying its
distribution to these types of areas. In addition, the information
states that recent records in upland habitats have occurred primarily
in areas associated with ``cultivated riparian'' habitats resulting
from the human influences of irrigation and ornamental plantings, such
as in suburban areas of Tucson (Johnson and Carothers 2008b, pp. 13-
14). We agree that riparian ecosystems provide important pygmy-owl
habitat within its range. However, we disagree with the suggestion that
pygmy-owls are riparian obligates, and thus limited in occurrence to
these areas. For example, there are numerous recent locations in which
pygmy-owls were detected in Sonoran desert uplands and semi-desert
grasslands of southern Pinal County, Avra Valley, Altar Valley, Cabeza
Prieta National Wildlife Refuge, Organ Pipe Cactus National Monument,
and northern Sonora that are not in proximity to ``cultivated
riparian'' or naturally occurring hydro- or mesoriparian (wet riparian)
habitats.
Two members of the public provided extensive information in support
of the idea that pygmy-owls have never been common in Arizona;
therefore, the current low numbers and reduced distribution are not
sufficient reason to determine that the pygmy-owl is endangered in
Arizona (James 2008, pp. 8-10; Parker 2008, pp. 2-10). This conclusion
is based on the historical records from early naturalists and
ornithologists regarding their observations or collections of pygmy-
owls or their nests or eggs, or the lack thereof. Specifically, this
information points out that a number of early naturalists or
ornithologists that made trips of various lengths and in various
locations in Arizona where pygmy-owls would have been expected to occur
did not make mention of observing pygmy-owls in their trip reports
(James 2008, pp. 46-48; Parker 2008, pp. 6-8). We appreciate the effort
and research represented by this information. It provides an excellent
summary of historical ornithological efforts in Arizona. In assessing
the information provided, we must determine if it is comparable to the
information currently available on pygmy-owl numbers and distribution
in Arizona. Current information comes from extensive surveys focused on
locating only pygmy-owls using tape-playback or call imitation to
locate the owls. We can find no evidence from the information provided
that this same effort or methodology was used to locate pygmy-owls in
the historical record; thus comparison with current surveys is not
appropriate.
We do not discount the ability of early naturalists and
ornithologists to find and identify pygmy-owls. However, finding pygmy-
owls was not the objective of the trips reported in the literature, and
unfortunately, most of these early reports do not contain enough
information for us to determine that the effort was adequate to find
pygmy-owls if they were present or that the absence of documentation of
pygmy-owls truly means that no pygmy-owls were encountered. Additional
information received from the public points out the problems in
interpreting these early reports, ``While certainly instructive as to
the critical value of surface water diversions, irrigation, and
agriculture to Cactus ferruginous pygmy owls, lack of necessary
specific information prevents Breninger's 1898
[[Page 61863]]
account from serving as a source of support for the petitioner's claim
that this owl was historically common across the lowlands of central
and southern Arizona. This is because Breninger neither shows how much
time he spent in the field nor the locations he actually visited along
either the Salt and Gila Rivers that caused him to conclude that Cactus
ferruginous pygmy owls were then ``of common occurrence'' ``among the
growth of cottonwood'' that fringed both on a highly localized basis''
(Parker 2008, pp. 3-4).
While early records provide information that shows the range of the
pygmy-owl has contracted in Arizona, this conclusion relies on
information at a large scale and is not dependent on specific
population numbers, only presence or absence. The logical assumption
may follow that pygmy-owl numbers are likely reduced as well. However,
these early records do not have enough specific information for us to
quantify historical pygmy-owl population numbers in a way that allows
comparison to our current information. Glinski (1998, p. 3) provides a
summary of this issue in The Raptors of Arizona, ``From the perspective
of the variety and numbers of raptors, what did Arizona's landscape
harbor two centuries ago? Is the answer to this question in the early
literature? Unfortunately, no. Detailed records that accurately depict
the status of Arizona raptors before 1970 are entirely lacking. The
records of early explorers are full of errors, and later
interpretations of them have added to the problem (G.P. Davis 1982).''
We received information from various agencies and municipalities
that contained survey results from Arizona indicating that the pygmy-
owl is likely absent from some areas in Maricopa and Pima Counties.
Survey data submitted by the USDA Forest Service covering over 4,050
hectares (ha) (10,000 acres (ac)) in a 6-year period on the Tonto
National Forest in Maricopa County detected no pygmy-owls (USFS 2008,
p. 1). Burger (2008, p.1) indicated that the Arizona Game and Fish
Department (AGFD) had conducted 3 years of surveys in Maricopa County
without any pygmy-owl detections. Annual pygmy-owl surveys have been
conducted by the Air Force on the Barry M. Goldwater Range of
southwestern Arizona from 1993 to the present with no verified pygmy-
owl detections (Uken 2008, p. 1). The Pima County Department of
Transportation conducts pygmy-owl surveys for their capital improvement
projects. These pygmy-owl surveys are associated with specific
projects, and do not represent systematic surveys throughout Pima
County. To date, they have conducted 383 surveys at 152 locations in
Pima County with no detections (Pima County 2008, p.1). Some of the
above surveys, and other negative surveys conducted throughout Arizona
since 1997, occurred in areas where the pygmy-owl was historically
located. This provides strong evidence that the current range of the
pygmy-owl in Arizona has contracted.
Currently in Arizona, the pygmy-owl is found only in portions of
Pima and Pinal Counties. The Arizona Breeding Bird Atlas reports
confirmed occurrences of the pygmy-owl in only three blocks distributed
in Pima and Pinal Counties (Arizona Breeding Bird Atlas (ABBA) 2005, p.
219). Twelve other blocks recorded probable (3) or possible (9)
occurrences, but none occurred outside of Pima and Pinal Counties (ABBA
2005, p. 219). Recent surveys indicate that probably fewer than 50
adult pygmy-owls exist in the state, with 10 or fewer nest sites on an
annual basis (Abbate et al. 2000, pp. 15-16, AGFD unpublished data).
However, since the pygmy-owl was delisted in 2006 (71 FR 194521; April
14, 2006), surveys, monitoring, and other research on pygmy-owls has
declined. Limited survey and monitoring in Arizona from 2009 to 2011
documented that pygmy-owls still occupy historical locations in the
Altar Valley, Avra Valley, and Organ Pipe Cactus National Monument, all
within Pima County (Service 2009b, p. 1; Tibbitts 2011, p. 1; Service
2011, p. 1). Comprehensive surveys have not been conducted on the
Tohono O'odham Nation (Nation), which is located in the central portion
of both the historical and current distribution of pygmy-owls in
Arizona. However, a number of surveys have been completed for various
utility projects on the Nation, and the pygmy-owl is known to occur
there. Distribution of the data from these surveys has been restricted
by the Nation and is not available for analysis. There are large areas
of suitable habitat on the Nation, but the information we have
indicates that pygmy-owls are patchily distributed, just as in other
areas of the State, and occur at similar densities.
In summary, because the early records found in the literature
provide no basis for consistent interpretation, the statements that the
pygmy-owl was ``not uncommon,'' ``of common occurrence,'' and ``fairly
numerous'' in lowland central and southern Arizona may be as
appropriate as the commenter's interpretation that the pygmy-owl was
never common in Arizona. The bottom line is that these early records
provided no quantifiable information on which to base trends in pygmy-
owl populations. Consequently, we must base our evaluation of the
current pygmy-owl status on the best available scientific and
commercial data, which is the information that does, at least, provide
some ability to quantify pygmy-owl population numbers. Regardless of
the lack of quantified historical data, the early records found in the
literature give us some idea of the historical distribution of the
pygmy-owl in Arizona that, when compared to the current distribution,
has unquestionably been reduced.
In Texas, the pygmy-owl was formerly common in the Rio Grande
delta. Griscom and Crosby (1926, p. 18) reported that the pygmy-owl was
considered a ``common breeding species'' in the Brownville region of
southern Texas. Even as late as 1950, Friedman et al. (1950, p. 145)
considered the pygmy-owl to be ``a very common breeding bird.''
However, Oberholser (1974, pp. 451-452) indicates that agricultural
expansion and subsequent loss of native woodland and thornscrub
habitat, beginning in the 1920s, preceded the rapid demise of the
pygmy-owl populations in the Rio Grande delta. By the 1970s, the pygmy-
owl was encountered only rarely in Texas.
Nonetheless, Wauer et al. (1993, pp. 1074-1076) indicate that
private ranches in Kenedy and Brooks Counties in Texas support a
``large and apparently thriving population of ferruginous pygmy-owls.''
Currently, the pygmy-owl is most consistently found only in the
southernmost counties in Texas, mainly in Starr and Kenedy Counties
(Tewes 1992, p. 21; Oberholser 1974, p. 451). More recent work
documents occupancy in Brooks and Kenedy Counties on the King Ranch and
adjacent ranches in Texas (Proudfoot 1996, p. 6; Mays 1996, p. 29).
Population estimates in Texas include estimates of greater than 100
owls in Kleberg County (Tewes 1992, p. 24), 654 pairs in Kenedy,
Brooks, and Willacy Counties (Wauer et al. 1993, p. 1074), and 745 to
1,823 pygmy-owls on ranches in Kenedy and Brooks Counties (Mays 1996,
p. 32).
Recent concern about the populations in Texas has been raised
because of an apparent decline in the number of pygmy-owl nestlings
banded as part of an ongoing nest box study in Texas (Proudfoot 2010,
p. 1). The numbers of nestlings banded at more than 200 nest boxes in
2003 and 2004 were 84 and 96 respectively. The numbers suggest a steady
decline from 2004 to 2010, with 25 and 24 nestlings banded in 2009 and
[[Page 61864]]
2010, respectively (Proudfoot 2010, p. 1). This represents an
approximate 70 percent decline in the number of nestlings banded over
an 8-year period. Proudfoot (2011b, p. 1) indicates this decline is
likely the result of the loss of suitable habitat around nest boxes due
to recent hurricanes and fires. Without a more comprehensive survey
effort in southern Texas, we cannot definitively state that the overall
population of pygmy-owls in south Texas matches the decline of
nestlings documented during this nest box study. However, it does raise
our level of concern for this population. More work is needed in Texas
to determine the overall population status and the extent of habitat
loss and fragmentation. It may simply be that the pygmy-owls in these
areas have moved to adjacent suitable habitat as former habitat and the
associated nest boxes have been destroyed.
The pygmy-owl occurs in portions of eight States in Mexico. The
pygmy-owl was thought to be uncommon throughout much of Sonora (Russell
and Monson 1998, p. 141; Hunter 1988, pp. 1-6). However, recent surveys
and capture efforts have shown that the pygmy-owl commonly occurs in
both northern and southern Sonora, but is uncommon or absent in central
Sonora (Flesch 2003, p. 39; AGFD 2008a, p.6; Service 2009a, p. 1). The
highest densities of pygmy-owls occurred in the Sinaloan deciduous
forest of southern Sonora (Flesch 2003, p. 42). Flesch (2003, p. 39)
documented 438 males, 74 females, and 12 pygmy-owls of unknown sex
along 1,113 kilometers (km) (1,780 miles (mi)) of transects in Sonora,
and an additional 112 pygmy-owls incidentally detected.
During capture efforts in 2008, AGFD (2008a, p. 6) documented
multiple pygmy-owls commonly responding at capture sites in the
thornscrub and tropical deciduous forests of southern Sonora. In areas
of central Sonora sampled by AGFD, some sites had no pygmy-owl
responses, but responses increased as sampling moved into northern
Sonora. These results are similar to patterns of occupancy documented
by Flesch (2003, p. 40). However, it is clear that the number and
density of pygmy-owls is higher in the thornscrub and deciduous forest
community types than in the Sonoran desert community type. This
occurrence and distribution agrees with conclusions found in the
literature (Hunter 1988, p. 7; Russell and Monson 1988, p. 141;
Shaldach 1963, p. 40). A total of 119 pygmy-owls were captured by AGFD
over 15 days of trapping in northern Sinaloa and Sonora (AGFD 2008a, p.
6). The most recent monitoring of pygmy-owls in northern Sonora showed
that, in 2010, sites sampled had the highest occupancy rates in the
past 10 years at nearly 64 percent (Flesch 2011, p. 1). However, early
results from the 2011 monitoring show occupancy of these same sites at
around 50 percent, not far from the 10-year low of 45.7 percent (Flesch
2011, p. 1).
In summary, recent surveys and research in northwestern Mexico
indicate that numbers and density of pygmy-owls are higher in
thornscrub and tropical deciduous forest communities of southern Sonora
and Sinaloa than in the Sonoran desertscrub and semi-desert grassland
vegetation communities of the Sonoran Desert Ecoregion (Flesch 2003,
pp. 39-42; AGFD 2008a, p. 6).
The best available information we have from the literature for the
southern portion (areas south of Sonora and northern Sinaloa) of the
pygmy-owl range indicates that pygmy-owls are one of the most common
birds collected in these areas (Cartron et al. 2000, p. 5; Enriquez-
Rocha et al. 1993, p. 154; Binford 1989, p. 132; Hunter 1988, p. 7;
Johnsgard 1988, p. 161; Oberholser 1974, p. 451; Schaldach 1963, p.
40). It is important to note, however, that most of these references
apply to the ferruginous pygmy-owl as a species and not to the cactorum
subspecies specifically. However, the more recent survey, monitoring,
and capture work discussed above all occurred within the range of the
cactorum subspecies.
Tewes (1993, pp. 15-16) provides the most current information on
pygmy-owls in northeastern Mexico. During surveys in 1991, he estimated
96 pygmy-owls in association with 142 plots at 12 locations (Tewes
1993, pp. 15-16). He concludes that no published empirical evidence
suggests any change in the distribution of this species in Texas or
northeastern Mexico, although the likelihood of finding pygmy-owls is
low in some historically occupied areas (Tewes 1993, p. 22).
In addition, pygmy-owls are not evenly distributed across their
current range; rather they tend to be patchily distributed across the
landscape. Pygmy-owl populations, particularly in the northern portion
of its range, likely function as metapopulations (a group of spatially
separated populations that act at some levels as a single large
population). Genetic and population support for individual groups of
pygmy-owls likely occurs as a result of dispersal. Therefore, habitat
connectivity among these population groups is important to maintain
genetic diversity, as well as demographic support. Interaction among
these population groups likely varies with distance, but pygmy-owls
have been documented to disperse up to 260 km (161 mi.) (AGFD 2008a, p.
5). Individual pygmy-owl groups throughout the range are important to
the survival of the subspecies as a whole in providing metapopulation
support.
In conclusion, pygmy-owl distribution in the United States has
contracted, with pygmy-owls no longer found in Maricopa, Cochise, Yuma,
and Santa Cruz Counties in Arizona, nor in the Lower Rio Grande Valley
in Texas. Despite this range contraction in the United States, pygmy-
owls remain in Arizona and Texas. Survey results for Arizona indicate
that approximately 50 adult pygmy-owls remain. In addition, there are a
few large expanses of Arizona with suitable pygmy-owl habitat that have
not been completely surveyed or for which pygmy-owl information is not
available for evaluation. Pygmy-owl populations in Texas are estimated
to range up to 1,800 birds, although there have been some declines in
pygmy-owl nestlings associated with a nest box study in Texas. Pygmy-
owls are still found in Sonora and northern Sinaloa, with higher
densities reported in thornscrub and dry tropical forested areas
compared to the arid desert areas. Based on Tewes study (1993, entire),
pygmy-owls still occupy suitable habitat in northeastern Mexico and the
pygmy-owl's distribution remains unchanged in Texas and northeastern
Mexico. In addition, it appears that pygmy-owls still occur in the same
areas of Mexico reported in the literature, suggesting that the current
distribution is similar to the historical distribution. The available
information, although dated, suggests that pygmy-owls remain common in
the southern portion of their range.
Habitat
Pygmy-owls are found in a variety of vegetation communities,
including Sonoran desertscrub and semidesert grasslands in Arizona and
northern Sonora, thornscrub and dry deciduous forests in southern
Sonora south to Michoac[aacute]n, and Tamaulipan brushland in Texas and
northeastern Mexico. However, available information regarding specific
pygmy-owl habitat elements within these vegetation communities is
limited to Arizona, Texas, and northern Sonora.
In Arizona, pygmy-owls rarely occur below 300 meters (m) (1,000
feet (ft)) or above 1,200 m (4,000 ft) (Proudfoot and Johnson 2000, p.
5), except perhaps during dispersal (AGFD 2008b, p. 3). Historically,
in Arizona, the pygmy-owl
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nested in Fremont cottonwood-mesquite forests and mesquite bosques
(woodlands) associated with major drainages and their tributaries and
the subspecies is considered by some to be a preferential riparian
nesting species. The pygmy-owl in Arizona also occupies upland Sonoran
desertscrub, often associated with xeroriparian areas. Species
associated with these areas are Prosopis spp. (mesquite), Parkinsonia
spp. (palo verde), Acacia spp. (acacia), Olneya tesota (ironwood), and
Carnegiea gigantea (saguaro cactus) (Proudfoot and Johnson 2000, p. 5).
In Texas, the pygmy-owl was historically found in Prosopis spp.,
Ebenopsis ebano (ebony), and Arundinaria gigantea (cane) along the Rio
Grande River, and a more general distribution in riparian trees, brush,
palm, and mesquite thickets (Oberholser 1974, p. 451). It is now found
primarily in undisturbed live oak-mesquite forests and mesquite brush,
ebony, and riparian areas of the historical Wild Horse Desert north of
Brownsville, Texas (Proudfoot and Johnson 2000, p. 5).
In Mexico, the pygmy-owl occurs from sea level to 1,200 m (4,000
ft) (Friedmann et al. 1950, p. 145). In Sonora, it was originally
common in the lower Sonoran and Tropical Zones, primarily in giant
cactus associations (van Rossem 1945, p. 111). The subspecies is
resident throughout most of the desertscrub, tropical thornscrub, and
dry subtropical forests of Sonora, being most common in the latter
association (Russell and Monson 1998, p. 141). The pygmy-owl is absent
from tropical deciduous forests and higher vegetation zones in west
Mexico, where it is replaced by the least pygmy-owl (Glaucidium
minutissimum) and the northern pygmy-owl (G. gnoma) (Schaldach 1963, p.
40; Buchanan 1964, pp. 104-105), as well as the Colima pygmy-owl (G.
palmarum) (Howell and Robbins 1995, pp. 19-20). Dry, subtropical
forests provide important pygmy-owl habitat elements, as evidenced by
pygmy-owls being more common in this vegetation community type than in
other community types in Mexico. The dry, subtropical forests comprise
the majority of the pygmy-owl's southern range in Mexico. The presence
of large trees and columnar cacti for nesting, and diversity of cover
and prey types, contribute to the value of dry subtropical forests as
pygmy-owl habitat.
The pygmy-owl is a creature of edges found in semi-open areas of
thorny scrub and woodlands in association with giant cacti, scattered
patches of woodlands in open landscapes, mostly dry woods, and
evergreen secondary growth (K[ouml]nig et al. 1999, p. 373). It is
often found at the edges of riparian and xeroriparian drainages and
even habitat edges created by villages, towns, and cities (Proudfoot
and Johnson 2000, p. 5; Abbate et al. 1999, pp. 14-23). The pygmy-owl
is a secondary cavity nester, and nests occur within woodpecker holes
and natural cavities in giant cacti, but also in trees and even in a
sand bank (Flesch 2003, pp. 130-132; Proudfoot and Johnson 2000, p. 11;
Russell and Monson 1998, p. 141; Johnsgard 1988, p. 162). Tewes (1992,
p. 22) contends that status and occurrence of the pygmy-owl is related
to the availability of nest cavities.
While native and nonnative plant species composition differs among
the various locations within the range of the pygmy-owl, there are
certain unifying characteristics such as the presence of vegetation in
fairly dense thickets or woodlands; the presence of trees, saguaros,
Stenocereus thurberi (organ pipe cactus), or other columnar cacti large
enough to support cavities for nesting; and elevations typically below
1,200 m (4,000 ft) (Swarth 1914, p. 31; Karalus and Eckert 1974, p.
218; Monson and Phillips 1981, pp. 71-72; Johnsgard 1988, Enriquez-
Rocha et al. 1993, p. 158; Proudfoot 1996, p. 75; Proudfoot and Johnson
2000, p. 5). Large trees provide canopy cover and cavities used for
nesting, and the density of mid- and lower-story vegetation provides
foraging habitat and protection from predators and contributes to the
occurrence of prey items (Wilcox et al. 2000, pp. 6-9).
Life History
Usually, pygmy-owls first nest as yearlings (Proudfoot and Johnson
2000, p. 13; Abbate et al. 1999, pp. 17-19), and both sexes breed
annually thereafter. Territories normally contain several potential
nest and roost cavities from which responding females select a nest.
Hence, cavities per unit area may be a fundamental criterion for
habitat selection. Historically, pygmy-owls in Arizona used cavities in
cottonwood, mesquite, and ash trees, and saguaro cacti for nest sites
(Millsap and Johnson 1988, pp. 137-138). Recent information from
Arizona indicates nests were located in cavities in saguaro cacti for
all but two of the known nests documented from 1996 to 2002 (Abbate et
al. 1996, p. 15; 1999, p. 41; 2000, p. 13; AGFD 2003, p. 1). Pygmy-owl
nests in Texas were primarily in mesquite and live oak trees (Proudfoot
1996, pp. 36-38), and nests in Sonora, Mexico, were nearly always in
columnar cacti (Flesch and Steidl 2002, p. 6). Pygmy-owls will also use
nest boxes for nesting (Proudfoot 1996, p. 67).
Pygmy-owls begin courtship and advertisement calls early in the
year from January into February. Nest selection then occurs, with eggs
typically being laid from late March into June. Average clutch size as
reported by Johnsgard (1988, p. 162) for the United States and Mexico
was 3.3 (range 2 to 5, n = 43). In Texas, Proudfoot and Johnson (2000,
p. 11) report an average clutch size of 4.9 (range 3 to 7, n = 58).
First eggs hatch generally around mid-May, and fledging occurs from
late-May through June. The first dispersal of fledglings in Arizona and
Texas was documented as July 24th and August 14th, respectively
(Proudfoot and Johnson 2000, p. 10). Pygmy-owl juveniles typically
disperse at 8 weeks post-fledging. Males typically disperse shorter
distances than females. Dispersal distance ranges from 2.5 to 20.91 km
(1.55 to 13.00 mi) in Arizona (Abbate et al. 2000, p. 21) and 16 to 31
km (9.6 to 18.6 mi) in Texas (Proudfoot and Johnson 2000, p. 13). One
juvenile female pygmy-owl in Arizona recently dispersed a total of 260
km (161 mi) between August 2003 and April 2004 (AGFD 2008a, p. 5). In
Sonora, Mexico, Flesch and Steidl (2007, p. 37) documented dispersal
distances ranging from 1.1 to 19.2 km (0.7 to 11.5 mi).
Pygmy-owls are considered nonmigratory throughout their range.
There are winter (November to January) pygmy-owl locations from
throughout their historical range in Arizona (University of Arizona
1995, pp. 1-2; Snyder 2005, pp. 4-5; Abbate et al. 1999, pp. 14-17;
2000, pp. 12-13) and also in Texas (Proudfoot 1996, p. 19; Mays 1996,
p. 14). These winter records suggest that pygmy-owls are found within
their home ranges throughout the year and that they do not migrate
seasonally. The pygmy-owl is primarily diurnal (active during daylight)
with crepuscular (active at dawn and dusk) tendencies.
The pygmy-owl is a perch-and-wait hunter. It is largely a
generalist with regard to prey and diet. Oberholser (1974, p. 451)
indicated that the pygmy-owl's diet included lizards, large insects,
rodents, and birds (some as large as the owl). In Texas, insects,
reptiles, birds, small mammals, and amphibians, to a lesser extent, are
eaten by pygmy-owls (Proudfoot and Johnson 2000, p. 6). In Arizona,
reptiles, birds, small mammals, and insects have all been recorded in
the diet of the pygmy-owl (Abbate et al. 1999, pp. 35-40). Seasonal and
annual variations in diet occur throughout its range (Proudfoot
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and Johnson 2000, p. 6; Abbate et al. 1999, pp. 35-40).
The pygmy-owl is commonly mobbed (harassed) by many species of
passerines, presumably in response to being a regular predator on those
species (Proudfoot and Johnson 2000, p. 10; Abbate et al. 1999, pp. 25-
26; Hunter 1988, p. 1). The mobbing behavior of birds can often aid in
locating a well hidden pygmy-owl, as multiple individuals and species
will often participate in the mobbing and identify the perch of the
pygmy-owl. The dark eye-spots on the back of the pygmy-owl's head may
act to fend off mobbing or increase predatory efficiency by confusing
prey (Heinrich 1987 in Proudfoot and Johnson 2000, p. 10).
Due to their small size and occurrence in similar habitats as many
of their predators, pygmy-owls are preyed upon by a variety of species.
Documented and likely predators in Texas and Arizona include raccoons
(Procyon lotor), great horned owls (Bubo virginianus), Cooper's hawks
(Accipiter cooperii), Harris' hawks (Parabuteo unicinctus), western
screech owls (Megascops kennicottii), bull snakes (Pituophis
melanoleucus), and domestic cats (Felis domesticus) (Abbate et al.
1999, p. 27; Proudfoot and Johnson 2000, p. 10). Pygmy-owls may be
particularly vulnerable to predation and other threats during and
shortly after fledging (Abbate et al. 1999, p. 50). Lifespan has been
documented to be 7 to 9 years in the wild (Proudfoot 2009b, p. 1) and
10 years in captivity (AGFD 2009, p. 1).
Summary of Information Pertaining to the Five Factors Affecting the
Pygmy-Owl Throughout Its Range
Section 4 of the Act (16 U.S.C. 1533) and implementing regulations
(50 CFR 424) set forth procedures for adding species to, removing
species from, or reclassifying species on the Federal Lists of
Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of
the Act, a species may be determined to be endangered or threatened
based on any of the following five factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
In making our 12-month finding on the petition we considered and
evaluated the best available scientific and commercial information.
In considering whether the five statutory factors in section 4(a)
might constitute threats, we must look beyond the mere exposure of the
species to the factor and determine whether the species responds to the
factor in a way that causes actual negative impacts to the species. If
there is exposure to a factor, but no response, or only a positive
response, that factor is not a threat. If there is exposure and the
species responds negatively, the factor may be a threat and we then
attempt to determine how significant a threat it is. If the threat is
significant, it may drive or contribute to the risk of extinction of
the species such that the species warrants listing as threatened or
endangered as those terms are defined by the Act. This does not
necessarily require empirical proof of a significant threat. The
combination of exposure and some corroborating evidence of how the
species is likely impacted could suffice. The mere identification of
factors that could impact a species negatively is not sufficient to
compel a finding that listing is appropriate; we require evidence that
these factors are operative threats that act on the species to the
point that the species meets the definition of threatened or endangered
under the Act. A species may be threatened or endangered based on the
intensity or magnitude of one operative threat alone or based on the
synergistic effect of several operative threats acting in concert.
Through our five-factor analysis, we identified a number of factors
negatively impacting the pygmy-owl or its habitat. To determine whether
these impacts individually or collectively rise to the level of threats
such that the pygmy-owl is in danger of extinction throughout its
range, or likely to become so in the foreseeable future, we first
considered whether these impacts to the subspecies were causing long-
term, range-wide, population-scale declines in pygmy-owl numbers, or
were likely to do so in the foreseeable future. Although some of these
impacts seem significant individually, we found these impacts to be
localized in their effects, but not placing the pygmy-owl in danger of
extinction throughout its range now or in the foreseeable future. In
other words, the severe impacts were restricted to an area that
constitutes a relatively small portion of the pygmy-owl's range.
The detailed information we have on impacts covers only about 27
percent of the pygmy-owl's range. For this area, which includes Arizona
and Texas in the United States, and Sonora and northern Sinaloa in
Mexico, information describing the impacts to pygmy-owls was relatively
complete. For the remaining 73 percent of the pygmy-owl range in
Mexico, information regarding impacts to pygmy-owls was relatively
sparse. The best available scientific and commercial information
indicates that the impacts to pygmy-owls in the northern portion of
their r