Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Gunnison's Prairie Dog as Threatened or Endangered, 6660-6684 [08-493]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 73, Number 24 (Tuesday, February 5, 2008)]
[Proposed Rules]
[Pages 6660-6684]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 08-493]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[FWS-R6-ES-2008-0013; 1111 FY07 MO-B2]


Endangered and Threatened Wildlife and Plants; 12-Month Finding 
on a Petition To List the Gunnison's Prairie Dog as Threatened or 
Endangered

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of a 12-month petition finding.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce our 
12-month finding on a petition to list the Gunnison's prairie dog 
(Cynomys gunnisoni) as an endangered or threatened species under the 
Endangered Species Act of 1973, as amended (Act). After a thorough 
review of all available scientific and commercial information, we find 
that the species is not threatened or endangered throughout all of its 
range, but that the portion of the current range of the species located 
in central and south-central Colorado and north-central New Mexico (the 
northeastern portion of the range) represents a significant portion of 
the range where the Gunnison's prairie dog is warranted for listing 
under the Act. Currently, listing is precluded by higher priority 
actions to amend the Lists of Endangered and Threatened Wildlife and 
Plants. We have assigned a listing priority number (LPN) of 2 to this 
species, because threats have a high magnitude, and are imminent. We 
will develop a proposed rule to list the Gunnison's prairie dog in the 
northeastern (montane) portion of its range as our priorities allow.

DATES: This finding was made on February 5, 2008.

ADDRESSES: This finding is available on the Internet at https://
www.regulations.gov and https://www.fws.gov/mountain-prairie/species/
mammals/gunnisonprairiedog. Supporting documentation we used to prepare 
this finding is available for public inspection, by appointment, during 
normal business hours at the U.S. Fish and Wildlife Service, Western 
Colorado Field Office, 764 Horizon Drive, Building B, Grand Junction, 
CO 81506-3946; telephone (970) 243-2778; facsimile (970) 245-6933. 
Please submit any new information, materials, comments, or questions 
concerning this finding to the above address.

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FOR FURTHER INFORMATION CONTACT: Al Pfister, Field Supervisor, U.S. 
Fish and Wildlife Service, Western Colorado Field Office (see 
ADDRESSES). If you use a telecommunications device for the deaf (TDD), 
call the Federal Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION: 

Background

    Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.), requires 
that, for any petition containing substantial scientific and commercial 
information that listing may be warranted, we make a finding within 12 
months of the date of receipt of the petition on whether the petitioned 
action is--(a) not warranted, (b) warranted, or (c) warranted, but that 
immediate proposal of a regulation implementing the petitioned action 
is precluded by other pending proposals to determine whether species 
are threatened or endangered, and whether 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 on the date 
of such finding; that is, requiring a subsequent finding to be made 
within 12 months. We must publish these 12-month findings in the 
Federal Register.

Previous Federal Actions

    On February 23, 2004, we received a petition from Forest Guardians 
and 73 other organizations and individuals requesting that the 
Gunnison's prairie dog (found in Arizona, Colorado, New Mexico, and 
Utah) be listed as threatened or endangered.
    On July 29, 2004, we received a 60-day notice of intent to sue for 
failure to complete a finding. On December 7, 2004, an amended 
complaint for failure to complete a finding for this and other species 
was filed. We reached a settlement agreement with the plaintiffs, and 
on February 7, 2006, we published a 90-day finding in the Federal 
Register (71 FR 6241) determining that the petition did not present 
substantial scientific information indicating that listing the 
Gunnison's prairie dog species may be warranted.
    On August 17, 2006, Forest Guardians and eight other organizations 
and individuals provided written notice of their intent to sue 
regarding the determination in the 90-day finding. On December 13, 
2006, the plaintiffs filed a complaint challenging the finding. On June 
29, 2007, we reached a settlement agreement with the plaintiffs for 
submittal to the Federal Register of a 12-month finding by February 1, 
2008. The court adopted the terms and conditions of the agreement on 
July 2, 2007.
    On August 28, 2007, we published a notice initiating the 12-month 
finding and opening a 60-day public comment period on the Gunnison's 
prairie dog (72 FR 49245).

Species Information

    A description of the Gunnison's prairie dog is included in the 90-
day petition finding (71 FR 6241; February 7, 2006) and in a concise 
review of the published information by Underwood (2007, pp. 6-13). In 
addition, we used data in the Western Association of Fish and Wildlife 
Agencies' (WAFWA) Gunnison's Prairie Dog Conservation Assessment 
(Seglund et al. 2005) to complete much of our analysis in this finding.
    The Gunnison's prairie dog has sometimes been divided into two 
subspecies: Cynomys gunnisoni gunnisoni and C. g. zuniensis (Hollister 
1916, p. 29). We currently regard the Gunnison's prairie dog as a 
single species because the most recent published analyses (Goodwin 
1995, pp. 100, 101, 110; Pizzimenti 1975, pp. 11, 15, 63) do not 
support subspecies designation. Unpublished research (Hafner 2004, p. 
6; Hafner et al. 2005, p. 2) indicates that the distribution of 
mitochondrial DNA (deoxyribonucleic acid) haplotype lineages supports 
past geographic isolation, followed by limited mixing in regions 
coincident with the recognized borders of the two purported subspecies. 
Although this analysis will likely be substantiated through additional 
research, it is still preliminary and needs to be verified before we 
can use it as evidence for subspecies designation. For the same 
reasons, although Gunnison's prairie dogs in montane habitat may be 
``markedly separate'' from those in prairie habitat, we are not 
proposing listing the montane prairie dogs as a distinct population 
segment (DPS) under our Policy Regarding the Recognition of Distinct 
Vertebrate Population Segments Under the Endangered Species Act (61 FR 
4722; February 7, 1996). We anticipate that future funding may become 
available for genetic, taxonomic, and range research to determine 
whether subspecies or DPS status is valid.
    Gunnison's prairie dogs are a colonial species, historically 
occurring in large colonies over large areas. Colonial behavior offers 
an effective defense mechanism by aiding in the detection of predators, 
but it also can play an important role in the transmission of disease 
(Antolin et al. 2002, p. 19; Biggins and Kosoy 2001, p. 911). Complexes 
of Gunnison's prairie dog colonies (metapopulations) expand or contract 
over time depending upon various natural factors (such as reproduction, 
food availability, and disease) and human-caused factors (such as 
chemical control and shooting). To substantially augment depleted 
populations or replace populations without human intervention, a 
metapopulation structure is required across the landscape so that 
migration between colonies is possible (Gilpin and Soule 1986, p. 24; 
Clark et al. 1982, pp. 574-575; Lomolino and Smith 2001, p. 938).

Habitat

    Gunnison's prairie dog habitat includes level to gently sloping 
grasslands and semi-desert and montane shrublands, at elevations from 
6,000 to 12,000 feet (1,830 to 3,660 meters) (Bailey 1932, p. 125; 
Findley et al. 1975, p. 133; Fitzgerald et al. 1994, p. 183; Pizzimenti 
and Hoffman 1973, p. 1; Wagner and Drickamer 2002, p. 4). Grasses are 
the most important food item, with forbs, sedges, and shrubs also 
occasionally used (Pizzimenti and Hoffman 1973, p. 3; Shalaway and 
Slobodchikoff 1988, p. 840).
    Gunnison's prairie dog range can be considered to occur in two 
separate range portions--higher elevations in the northeast part of the 
range and lower elevations elsewhere (Bailey 1932, pp. 125-127; 
Pizzimenti and Hoffman 1973, pp. 1-2; Hall 1981, p. 7; Knowles 2002, p. 
4). We refer to these areas as montane and prairie, respectively, 
throughout the document to differentiate them; however, we recognize 
that these terms are an oversimplification of the actual habitats 
present, and describe them in more detail below.
    In Figure 1, we provide a map illustrating the division of the 
general range of the species into the northeastern (montane) and 
southwestern (prairie) portions. The outer boundary in Figure 1 is 
referenced from maps depicting the species' gross range (Hollister 
1916, p. 24; Pizzimenti and Hoffman 1973, p. 2; Pizzimenti 1975, p. 4; 
Hall 1981, p. 415; Knowles 2002, p. 6), and from maps of the species' 
range in Arizona (Hoffmeister 1986, p. 194), Colorado (Armstrong 1972, 
p. 139; Fitzgerald et al. 1994, p. 185), New Mexico (Findley et al. 
1975, p. 133), and Utah (Durrant 1952, p. 106). An approximate boundary 
dividing the montane and prairie range portions was established from 
several maps that recognize discrete range portions for each of the two 
purported subspecies,

[[Page 6662]]

Cynomys gunnisoni gunnisoni and C. g. zuniensis (Hollister 1916, p. 24; 
Armstrong 1972, p. 139; Pizzimenti and Hoffman 1973, p. 2; Pizzimenti 
1975, p. 4; Hall 1981). Maps that depict the geographic variation in 
Gunnison's prairie dog mitochondrial DNA in southern Colorado and 
northern New Mexico (Hafner 2004, p. 6; Hafner et al. 2005, p. 2) were 
used to improve the resolution of the montane and prairie boundary in 
this region, as these maps provide a boundary based on genetic 
differences between Gunnison's prairie dogs in the two range portions. 
Lastly, we used topographic maps to adjust the boundary on a finer 
scale along the mountain ranges and ridges of southern Colorado and 
northern New Mexico, because geography partly separates the Gunnison's 
prairie dog populations and allows limited overlap between the two 
range portions (Knowles 2002, p. 3; Hafner et al. 2005, p. 1).
    In summary, the maps we used to delineate the montane and prairie 
range portions vary in their age, projection, scale, and accuracy, and 
depict boundaries based on geography, morphological traits of 
Gunnison's prairie dog populations, and genetic characteristics from 
Hafner's work (Hafner 2004, p. 6; Hafner et al. 2005, p. 2). They 
contribute to the best available information used to establish the 
montane and prairie portions of the species' range for further 
analysis.
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Montane Habitat

    The northeastern range (central and south-central Colorado, and 
north-central New Mexico) consists primarily of higher elevation, 
cooler and more mesic plateaus, benches, and intermountain valleys. We 
call this portion ``montane'' for ease of reference, and it comprises 
approximately 40 percent of the total potential habitat within the 
current range. Gunnison's prairie dogs occupy grass-shrub areas in low 
valleys and mountain meadows within this habitat (Seglund et al. 2005, 
p. 12). The Gunnison's prairie dogs in this portion of the range are 
limited by pronounced physiographic barriers (Pizzimenti and Hoffman 
1973, p. 1), including the Uncompahgre Plateau and San Juan mountains 
in Colorado and Utah, and the Sangre de Cristo, San Juan, and Jemez 
mountain ranges in New Mexico.

Prairie Habitat

    The southwestern range (southeastern Utah, southwestern Colorado, 
northwestern New Mexico, and northeastern Arizona) consists primarily 
of lower elevation, warmer and more xeric plains and plateaus (Bailey 
1932, pp. 125-127; Pizzimenti and Hoffman 1973, pp. 1-2; Hall 1981, p. 
7; Knowles 2002, p. 4). We call this portion ``prairie'' for ease of 
reference, and it comprises approximately 60 percent of total potential 
habitat within the current range. Gunnison's prairie dogs occupy 
shortgrass and mid-grass prairies within this habitat (Seglund et al. 
2005, p. 12).

Distribution, Abundance, and Trends

    The current distribution of the species includes northeastern 
Arizona; central, south-central, and southwestern Colorado; north-
central and northwestern New Mexico; and extreme southeastern Utah 
(Bailey 1932, pp. 125-127; Pizzimenti and Hoffman 1973, pp. 1-2; Hall 
1981, p. 7; Knowles 2002, p. 4) (see Figure 1 above). Limited overlap 
occurs in the ranges of Gunnison's prairie dogs and black-tailed 
prairie dogs (Cynomys ludovicianus) in New Mexico (Goodwin 1995, p. 
101; Sager 1996, p. 1), and Gunnison's prairie dogs and white-tailed 
prairie dogs (Cynomys leucurus) in Colorado (Knowles 2002, p. 5), but 
we have no evidence that interbreeding is occurring. Currently, 27 
percent of potential Gunnison's prairie dog habitat occurs in Arizona, 
25 percent in Colorado, 45 percent in New Mexico, and 3 percent in Utah 
(Seglund et al. 2005, p. 83). We used the data in Seglund et al. (2005, 
pp. 82, 85-87) to calculate that approximately 22 percent of the 
potential habitat occurs on private lands, 12 percent on State lands, 
17 percent on Federal lands, and 49 percent on Tribal lands/Bureau of 
Indian Affairs (BIA). The Tribal lands habitat occurs mostly in Arizona 
and New Mexico; a large amount of potential habitat is on Navajo lands 
(Cole, p. 1).
    Most estimates of prairie dog populations in the available 
literature are expressed in terms of area (acres (ac) or hectares (ha)) 
of occupied habitat rather than in numbers of individuals, most likely 
because counting individuals is feasible only for small areas (Biggins 
et al. 2006, p. 94). Also, the number of animals present in a locality 
has been observed to vary with habitat, season, colony age, 
precipitation, forage, predation, disease, chemical control, shooting, 
and other factors (Knowles 2002, pp. 7-8); density of individuals 
typically ranges from 2 to 23 per ac (5 to 57 per ha) (Fitzgerald et 
al. 1994, p. 184). Most prairie dog surveys do not result in a density 
estimate because of the associated effort and cost. Estimates of 
Gunnison's prairie dog occupied habitat provide one of the best 
available and most reasonable means of evaluating the status of the 
species across its range.
    Obtaining estimates of occupied area is itself time-consuming and 
costly. Ground or aerial mapping of colonies over a predicted habitat 
range of 23 million ac (9.5 million ha) in 4 States would be required 
to determine a rangewide estimate of the area occupied by the 
Gunnison's prairie dog (Seglund et al. 2005, pp. 17-19). Recent 
attempts at less expensive aerial surveys (for example, air photo 
interpretation) have been limited in their effectiveness when applied 
to Gunnison's prairie dogs (Johnson et al. 2006, p. 3; Seglund et al. 
2005, pp. 23-24). Whether surveying is performed from the air or on the 
ground, it is often difficult to accurately and consistently discern 
colony boundaries (thus introducing error in the area measurements). 
Older studies did not benefit from technologies such as global 
positioning systems and geographic information systems (GIS) in mapping 
colonies. Accuracy suffers when studies are performed over the longer 
time intervals necessary to visit large range portions, because colony 
area, location, and persistence on the landscape often change 
relatively quickly (Wagner et al. 2006, p. 335).
    In summary, we recognize that different methodologies were used at 
different times and in different locales to derive the various 
historical occupied area estimates we obtained for review. These 
estimates contribute to the best available information, and we consider 
them comparable for determining long-term population trends, while 
acknowledging potential error margins on the scale of an order of 
magnitude.
    Since our 90-day finding in 2006, all States within the range of 
the species have applied occupancy modeling methodology to investigate 
the habitat occupied by Gunnison's prairie dogs. This is a newer 
technique that yields estimates of the percentage of random plots 
occupied across the habitat range under consideration (MacKenzie et al. 
2002, pp. 2248-2249; MacKenzie et al. 2003, pp. 2200-2201). These 
estimates are statistically based and, therefore, are considered more 
objective (Andelt et al. 2006, pp. 1-2; Colorado Division of Wildlife 
(CDOW) 2007, p. 19; WAFWA 2007, p. 4).
    A drawback is that estimates of percent occupancy by Gunnison's 
prairie dogs are not directly comparable to estimates of occupied acres 
(including most historic estimates), because when a random plot is 
visited, only detection or non-detection (not acres occupied) is 
recorded by the observers. If mapping is not performed during a site 
visit, no information about colony or complex size or location is 
obtained.
    The positive aspects of this method are statistical rigor, 
precision estimates, large-scale application in a single season, and 
trend analysis if performed over subsequent years. In addition, the 
results of individual surveys can be interpreted separately to assess 
prairie dog occupancy and document trends within in specific areas of 
concern. Although only a single year (2007) of occupancy modeling 
results are available (with the exception of Colorado data from 2005 
and 2007), we used these estimates, along with estimates of occupied 
areas, to assess the status and trends of the Gunnison's prairie dog in 
each of the four States.

Historical Estimates of Abundance

    Historical estimates of Gunnison's prairie dog occupied habitat in 
Arizona and New Mexico are available from Federal records of early 
poisoning efforts, such as by the Bureau of Land Management (BLM) and 
the U.S. Forest Service (USFS). In 1916, approximately 6.6 million ac 
(2.7 million ha) of Gunnison's prairie dog occupied habitat occurred in 
Arizona, and 11 million ac (4.4 million ha) occurred in New Mexico 
(Oakes 2000, pp. 169-171). In our 90-day finding in 2006 (71 FR 6241, 
February 7, 2006), we calculated historical estimates (circa 1916) for 
Colorado (6 million ac (2.4 million ha)) and Utah (700,000 ac (284,000 
ha)) from prairie dog information in various

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publications and reports, because data were not available for these 
States. By summation, based on the best available information, our 
rangewide estimate for historic (circa 1916) Gunnison's prairie dog 
occupied habitat was approximately 24 million ac (9.7 million ha).
    In 1961, an estimated 445,000 ac (180,000 ha) of habitat was 
occupied by Gunnison's prairie dog in Arizona; 116,000 ac (47,000 ha) 
in Colorado; 355,000 ac (144,000 ha) in New Mexico; and 100,000 ac 
(41,000 ha) in Utah (Bureau of Sport Fisheries and Wildlife 1961, pp. 
1, 5). By summation, the rangewide estimate for Gunnison's prairie dog 
occupied habitat in 1961 was approximately 1 million ac (405,000 ha). 
These data suggest that, from 1916 to 1961, Gunnison's prairie dog 
populations decreased by approximately 93 percent in Arizona, 98 
percent in Colorado, 97 percent in New Mexico, and 86 percent in Utah, 
or by approximately 95 percent rangewide. However, historic declines 
may not support a conclusive inference that current populations 
continue to decline.
    In summary, empirical data on acres occupied indicate that, between 
1916 and 1961, habitat occupied by the Gunnison's prairie dog 
throughout its range declined from approximately 24,000,000 ac 
(9,700,000 ha) to approximately 1,016,000 ac (406,400 ha).

Statewide Estimates of Abundance

    As indicated above, estimates of percent occupancy arrived at 
through recent occupancy modeling (presence or absence at a random 
plot) do not equate to acres occupied. The method currently used by 
States to assess the Gunnison's prairie dog's status, in conjunction 
with both historic and recent mapping efforts, provides empirical data 
on percent occupancy of potential habitat. This data is useful as a 
gross-scale comparison to historical estimates of acres occupied. Both 
types of data are valid and represent the best available science.
    Full occupancy of surveyed habitat would not directly equate to 100 
percent of available habitat, but it would provide a gross 
approximation of occupancy at a larger geographic scale. For the 
purposes of interpreting the percent occupancy numbers in this 
document, current State survey efforts utilize a scale from 1 to 100, 
indicating the percentage of occupied cells surveyed. Because we do not 
have historical data on percent of habitat occupied or on occupancy 
rates, we use the current percentage of occupied habitat to compare 
between habitats that currently appear to have a functional 
metapopulation structure (prairie) and that do not (montane). For 
example, the following paragraphs illustrate that Gunnison's prairie 
dog occupancy in plots sampled in montane habitat is estimated to be 
approximately 3.6 percent as compared to approximately 18.3 percent in 
plots sampled in prairie habitat in Colorado. Of the total montane 
habitat, approximately 85 percent occurs in Colorado.

Arizona

    In 2007, occupied habitat on non-Tribal lands in Arizona comprised 
approximately 108,570 ac (40,500 ha) (Underwood 2007, p. 30). No 
comprehensive data are available from Tribal lands in Arizona, which 
include 50 percent of the Statewide potential habitat. Therefore, the 
2007 estimate for Arizona (Underwood 2007, p. 30) is likely 
substantially less than what actually exists. Due to a lack of any 
Tribal estimates since 1961, recent population trends on Tribal lands 
statewide are unknown, but may have increased over the 1961 estimate of 
435,419 ac (176,207 ha). We are unaware of any disproportionate adverse 
effects to the species on Tribal lands during this interval, and we 
assume that habitat trends may have followed a similar pattern as on 
non-Tribal lands. All habitat within Arizona is considered prairie.

Colorado

    The Colorado Department of Agriculture (CDA 1990, p. A-3) solicited 
questionnaire responses from farmers and ranchers from which they 
extrapolated a 1990 estimate of 1,553,000 ac (621,200 ha) of occupied 
habitat for all 3 species of prairie dogs found in Colorado 
(Gunnison's, white-tailed, and black-tailed). Based on species 
occurrence by county, Seglund et al. (2005, p. 26) estimated that 
438,876 ac (177,607 ha) were occupied by Gunnison's prairie dogs.
    From 2002 to 2005, the Colorado Division of Wildlife (CDOW) 
interviewed field personnel from CDOW, the Service, the USFS, and the 
BLM regarding the habitat occupied by Gunnison's prairie dogs in the 
State. Colonies were mapped on 1:50,000 scale U.S. Geological Survey 
county sheets and were designated as ``active'' (known to have prairie 
dogs inhabiting the colony within the last 3 years); ``inactive'' 
(prairie dogs occurred in the area but have not been present in more 
than 3 years); or ``unknown'' (prairie dogs were known to occur 
historically, but current status was unknown). From this effort, CDOW 
estimated 182,237 ac (72,895 ha) of active colonies; 9,042 ac (3,617 
ha) of inactive colonies; and 171,970 ac (68,788 ha) of colonies in 
unknown status within Colorado (CDOW 2007, p. 3). These data suggest an 
increase over the historical 1961 estimate of 115,650 ac (46,802 ha) of 
occupied habitat in Colorado. We have no way of estimating what percent 
of this difference may be due to different mapping techniques. We 
believe that the difference is mostly due to an actual increase in 
prairie dogs, likely within the prairie portion of the range, because 
data from the montane portion of the range indicate significantly 
reduced occupancy rates (see additional analysis below). We used area 
estimates from 2002 to 2005 to compute a Statewide occupancy estimate 
of 2.1 percent (known active colony area divided by area of potential 
habitat) (CDOW 2007). However, the occupancy modeling studies performed 
in 2005 and 2007 in Colorado, including both prairie and montane 
portions of the range, yielded Statewide occupancy estimates of 7.5 and 
8.6 percent, respectively (Andelt et al. 2006, p. 15; CDOW 2007, p. 
19), and these estimates are considered more reliable.

Montane and Prairie Habitat in Colorado

    Within Colorado, CDOW has designated individual population areas to 
identify where Gunnison's prairie dogs exist and where management 
activities should be focused. The montane portion of the species' range 
in Colorado is composed of the Gunnison, San Luis Valley, South Park, 
and Southeast population areas. By using CDOW (2007, p. 28) estimates 
of potential habitat, we determined that the montane range portion in 
Colorado comprises about 80 percent (6.9 million of 8.5 million ac (2.8 
million of 3.4 million ha)) of the available Gunnison's prairie dog 
habitat in the State. However, the montane range portion only contains 
about 40 percent (73,861 of 182,237 ac (29,544 of 72,894 ha)) of the 
available Gunnison's prairie dog habitat occupied in the State, based 
on our calculations using CDOW mapped area data (CDOW 2007, p. 3).
    The La Plata--Archuleta and Southwest population areas, in the 
prairie portion of Colorado's Gunnison's prairie dog habitat, comprise 
about 20 percent of the Gunnison's prairie dog habitat and contain 
about 60 percent of habitat occupied in the State (CDOW 2007, pp. 3, 
19). The higher proportion of occupied habitat in the smaller prairie 
portion of the State indicates that Gunnison's prairie dogs are more 
abundant in the prairie habitat area.

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    The 2005 occupancy modeling studies also indicate a higher 
proportion of occupancy (16 percent) in the prairie portion of the 
range in Colorado, and a lower proportion of occupancy (3.2 percent) in 
the montane portion of the species' range in Colorado (Andelt et al. 
2006, p. 17; CDOW 2007, p. 19). When the study was repeated over the 
same plots in 2007, occupancy was again found to be higher (18.3 
percent) in the prairie portion and lower (3.6 percent) in the montane 
range portion in Colorado (CDOW 2007, p. 19).

New Mexico

    We have no current information on occupied habitat in New Mexico. 
The best available science is from Bodenchuck (1981 p. 1), who 
solicited questionnaire responses from agricultural producers in 1981. 
Respondents reported 107,574 ac (43,567 ha) of Gunnison's prairie dog 
occupied habitat. Bodenchuck (1981, p. 8) extrapolated a Statewide 
total of 348,000 ac (141,000 ha) of occupied habitat for the species. 
Oakes (2000, p. 216) questioned this extrapolation because of possibly 
faulty assumptions used to derive it. Knowles (2002, p. 22) estimated 
that 75,000 ac (30,000 ha) of occupied habitat existed in 1982. New 
Mexico Department of Game and Fish used Digital Orthophoto Quarter 
Quadrangles to estimate a minimum of 9,108 ac (3,689 ha) of occupied 
habitat Statewide in 2004 (Seglund et al. 2005, p. 23). However, this 
method appears to be hampered by inaccurate detection of disturbances, 
time elapsed since photography, time elapsed since ground mapping, 
temporal changes in prairie dog towns, and other factors (Seglund et 
al. 2005, p. 33). While these estimates have limited accuracy, general 
use in assessing Statewide occupied habitat indicates that Gunnison's 
prairie dogs appeared to be decreasing between 1961 and 2004.

Montane and Prairie Habitat in New Mexico

    New Mexico also includes both montane and prairie habitat. The 
montane habitat is geographically connected to the montane portion of 
the Gunnison's prairie dog habitat in Colorado. It comprises about 17 
percent of the Gunnison's prairie dog habitat in New Mexico; we do not 
have accurate data on total acres in New Mexico, and therefore do not 
provide an acre estimate for the montane portion. We have no data on 
the percent occupancy in this habitat.
    The prairie habitat in New Mexico comprises about 83 percent of the 
habitat; we do not have accurate data on total acres in New Mexico, and 
therefore do not provide an acre estimate for the prairie portion. We 
have no data on the percent occupancy in this habitat.

Utah

    The Utah Division of Wildlife Resources estimated that 22,000 ac 
(8,906 ha) of occupied Gunnison's prairie dog habitat existed in Utah 
in 1968 (Seglund et al. 2005, p. 35). Knowles (2002, p. 21) estimated a 
minimum of 3,678 ac (1,490 ha) of occupied habitat Statewide. The 
Statewide trend in occupied habitat appears to have decreased from 
100,000 ac (40,500 ha) in 1961 (Bureau of Sport Fisheries and Wildlife 
1961, p. 5), to 40,000 ac (16,000 ha) in 2007 (Lupis et al. 2007, p. 
3). The Gunnison's prairie dog occupancy in Utah was estimated to be 
15.7 percent in 2007 (Lupis et al. 2007, p. 3). We consider all 
Gunnison's prairie dog habitat in Utah as prairie.

Summary of Statewide Estimates of Abundance

    We have empirical data on Gunnison's prairie dog occupancy that 
indicate a large decline in rangewide occupied acres. We also have 
recent empirical data that indicates percent occupancy within two 
separate portions of the range is significantly different.
    Data on acres occupied indicate that between 1916 and the present, 
habitat occupied by Gunnison's prairie dogs throughout its range 
declined from approximately 24,000,000 ac (9,700,000 ha) to between 
340,000 and 500,000 ac (136,000--200,000 ha). This represents a 
rangewide decline of greater than 95 percent.

Summary of Factors Affecting the Species Rangewide

    Section 4 of the Act (16 U.S.C. 1533) and implementing regulations 
at 50 CFR 424, set forth procedures for adding species to the Federal 
Lists of Endangered and Threatened Wildlife and Plants. In making this 
finding, we summarize below information regarding the status and 
threats to the Gunnison's prairie dog in relation to the five factors 
provided in section 4(a)(1) of the Act.
    In making this 12-month finding, we have considered all scientific 
and commercial information received or acquired between the time of the 
initial petition (February 23, 2004) and the end of the most recent 
public comment period (October 29, 2007), and additional scientific 
information from ongoing species surveys and studies as they became 
available.
    Under section (4) of the Act, we may determine a species to be 
endangered or threatened on the basis of any of the following five 
factors: (A) Present or threatened destruction, modification, or 
curtailment of habitat or range; (B) overutilization for commercial, 
recreational, scientific, or educational purposes; (C) disease or 
predation; (D) inadequacy of existing regulatory mechanisms; or (E) 
other natural or manmade factors affecting its continued existence. We 
evaluated whether threats to the Gunnison's prairie dog may affect its 
survival. Our evaluation of threats, based on information provided in 
the petition, available in our files, and available in published and 
unpublished studies and reports, is presented below.

A. The Present or Threatened Destruction, Modification, or Curtailment 
of its Habitat or Range

    Agricultural land conversions historically had a significant impact 
on Gunnison's prairie dog habitat (Knowles 2002, p. 12). Gunnison's 
prairie dogs have been displaced from some of the more productive 
valley bottomlands in Colorado and New Mexico (Longhurst 1944, p. 36). 
Agriculture currently impacts 2,063,930 ac (834,243 ha), or less than 
three percent, of the Gunnison's prairie dog range (Seglund et al. 
2005, p. 43). Seglund et al. (2005, p. 41) indicate agriculture is not 
a major rangewide threat because of the small percentage of the range 
affected, but also because agriculture provides highly productive 
forage in place of the native arid landscape. Current adverse impacts 
relate to secondary actions at a local scale, such as prairie dog 
control (for example, poisoning, shooting) in areas where prairie dogs 
occupy lands used for agriculture, particularly private lands. We 
assess shooting under Factor C, poisoning under Factor E, and both in 
Factor D.
    Urbanization also has caused habitat loss for Gunnison's prairie 
dog. Seglund et al. (2005, p. 41) determined that urbanization affects 
577,438 ac (233,681 ha) within the range of the species (less than two 
percent of the range). However, it appears this analysis considered 
only the direct effects of habitat loss. Urbanization also exerts 
indirect effects (for example, poisoning and shooting of prairie dogs), 
extending a human ``disturbance zone'' outward from the actual 
development footprint.
    Lower-density suburban development occurring in the southern Rocky 
Mountains is scattered and results in a fragmenting of habitats. In 
Colorado, urban development on the west slope of the Rocky Mountains 
(montane habitat) is occurring rapidly; 38 percent of Gunnison's 
prairie dog range is predicted to be impacted by low urban development 
(less than 40 units per ac;

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99 per ha), 6 percent by moderate development (40 to 80 units per ac; 
99 to 198 per ha), and 5 percent by high development (fewer than 80 
units per ac) between 2000 and 2020 (CDOW 2007, p. 28). We do not have 
information on the extent of development projected to occur in the 
other States within the species' range (Utah, Arizona, and New Mexico). 
Potential threats to Gunnison's prairie dog populations due to urban 
and suburban development exist, but have not been quantified, in the 
four cities of Santa Fe and Albuquerque, New Mexico; Flagstaff, 
Arizona; and Gunnison, Colorado (CDOW 2007, p. 4). In some areas, 
Gunnison's prairie dogs threatened by urban development have been 
captured and relocated to preserves or other nearby habitats, 
mitigating effects to overall population numbers, but not to area of 
habitat.
    Although urban and suburban development exert adverse impacts on 
Gunnison's prairie dog populations at a local scale, they likely affect 
less than three percent of the species' range; low density development 
appears to be compatible with continued use by prairie dogs, due to the 
offsets provided by lawns and pastures that provide high quality forage 
(Seglund et al. 2005, p. 41).
    Noxious weeds can increase in the presence of livestock 
overgrazing, and a relationship likely exists between overgrazing, 
Bromus tectorum (cheat grass) proliferation, and increased fire 
frequency and intensity (Seglund et al. 2005, p. 43). However, we have 
no data that quantifies these factors or their correlation with effects 
to Gunnison's prairie dog populations. The impact of overgrazing on 
prairie dog populations is contradictory. Some reports have noted that 
species density is positively correlated with the number of native 
plants (Slobodichikoff et al. 1988, p. 406), and that grazing has 
decreased forage availability (Seglund et al. 2005, p. 42). Other 
reports have concluded that prairie dog density is positively 
correlated with an increase in grazing, which simulates the shortgrass-
type of prairie environment preferred by prairie dogs (Fagerstone and 
Ramey 1996, p. 88; Marsh 1984, p. 203, Slobodchikoff et al. 1988, p. 
406). Considering the conflicting conclusions of published literature, 
and the lack of large-scale population decreases due to habitat 
alterations from livestock grazing, we find this is not a significant 
threat to the Gunnison's prairie dog.
    Numerous land parcels within the Gunnison's prairie dog range are 
leased for oil and gas development (Seglund et al. 2005, pp. 36, 42). 
However, no information is available that quantifies the amount of 
occupied habitat affected. In a study of white-tailed prairie dogs, 
Menkens and Anderson (1985, p. 13) concluded that any impact from 
seismic testing is negligible. However, we acknowledge that oil and gas 
development is rapidly occurring (Seglund et al. 2005, p. 44), and that 
this potential threat should be considered more closely when more 
accurate data are available.
    Road-related Gunnison's prairie dog mortality exists in proximity 
to specific population areas. Roads may be increasing due to oil and 
gas development. However, no studies quantify road mortality of 
Gunnison's prairie dogs. We have no data indicating that roads are 
currently threatening the species rangewide, and we conclude that 
prairie dog populations are able to recover from individual losses due 
to road mortality.
    Conservation principles indicate that smaller, more isolated 
populations are more vulnerable to extirpation (Barnes 1993, p. 34; 
Cully 1993, p. 43; Fitzgerald 1970, p. 78; Gilpin and Soule 1986, pp. 
30-31; Miller et al. 1994, p. 151; Mulhern and Knowles 1995, p. 21; 
Wilcox and Murphy 1985, p. 883; Wuerthner 1997, p. 464). Lomolino et 
al. (2003, p. 116) found that persistence of Gunnison's prairie dog 
colonies increased significantly with larger colony size and decreased 
isolation. However, we found no studies or data that specifically 
assess the magnitude of the threats discussed under Factor A 
(agriculture land conversions, urbanization, grazing, roads, and oil 
and gas leasing) and resulting fragmentation throughout the range of 
Gunnison's prairie dog habitat.

Summary of Factor A

    After assessing the best available science on the magnitude and 
extent of the effects of agricultural land conversion, urbanization, 
grazing, roads, oil and gas development, and fragmentation of habitat, 
we find that the destruction, modification, and curtailment of 
Gunnison's prairie dog's habitat or range are not significant threats. 
Agriculture, urbanization, roads, and oil and gas development each 
currently affect a small percentage of Gunnison's prairie dog habitat. 
Effects of livestock grazing, while widespread, have not resulted in 
measurable population declines. However, we need more information on 
the impacts of fragmentation and isolation with regard to persistence 
of prairie dog populations and on the magnitude of the potential threat 
posed by increasing oil and gas development.

B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

    Gunnison's prairie dogs have been historically subjected to 
recreational shooting and shooting as a form of pest management on 
ranch and agricultural land; these practices continue under current 
State regulations (see Factor D. Inadequacy of Existing Regulatory 
Mechanisms). Prairie dogs are especially vulnerable to shooting due to 
their colonial behavior, which facilitates easy access to many 
individuals at once (Seglund et al. 2005, p. 48). Most field studies on 
the effects of shooting prairie dogs have been carried out on black-
tailed prairie dogs, but we consider the results relevant to Gunnison's 
prairie dogs (CDOW 2007, p. 41). Shooting effects include population 
reduction and alteration of behavior, such as decreased foraging rates 
and increased vigilance, which reduce individual prairie dog vigor and 
result in lower reproductive output (Knowles 1988, p. 54; Reeve and 
Vosburgh in press, p. 5; Vosburgh 1996, pp. 32-33; Vosburgh and Irby 
1998, p. 368; Pauli and Buskirk 2007, pp. 1223-1224).
    Recreational shooting can reduce prairie dog population density at 
specific sites (Knowles 2002, p. 14; Miller et al. 1993, p. 91; 
Vosburgh 1996, pp. 13-14; Vosburgh and Irby 1998, pp. 366-367). Local 
extirpation of colonies may have occurred in isolated circumstances in 
the past (Knowles 1988, p. 54). However, increased population growth 
rates or recovery from very low numbers following shooting also have 
been reported (Knowles 1988, p. 54; Reeve and Vosburgh in press, p. 7). 
Recent studies of the effects of shooting on black-tailed prairie dogs 
appear to contradict the idea that populations quickly rebound from 
shooting. Reproductive output on colonies subjected to shooting 
decreased by 82 percent, while control colonies maintained a stable 
reproductive rate over the same period (Pauli and Buskirk 2007, p. 
1228). Therefore, black-tailed prairie dogs do not appear to rebound 
quickly from shooting.
    The International Union for the Conservation of Nature/Species 
Survival Commission (IUCN/SSC) Conservation Breeding Specialist Group 
evaluated the effects of shooting mortality on population viability of 
Gunnison's prairie dogs (CDOW 2007, p. 124). Simulations were run with 
a shooting closure in place from March 1 through June 14 each year 
(approximating State closures) and without any closures. Having the 
closure in place resulted in positive population growth and

[[Page 6668]]

negligible risk of extinction, except in scenarios with the highest 
levels (20 percent) of shooting-based mortality. Simulations run 
without the seasonal shooting closure in place suggest that when 
initial population sizes are smaller (less than 250 individuals) and 
shooting mortality is high (20 percent), a decrease in growth rate and 
an increase in population extinction risk exist (CDOW 2007, pp. 135-
137). Colorado, Utah, and Arizona (outside Tribal lands) have 
implemented seasonal closures on prairie dog shooting. In Arizona and 
New Mexico, the Navajo Nation monitors this threat but currently 
implements no closures on shooting because it finds the level of 
shooting to be low on its lands (Cole 2007, p. 4).

Summary of Factor B

    We have determined that shooting continues to be a threat to the 
Gunnison's prairie dog throughout all of its range and contributes to 
the decline of the species when combined with the effects of disease 
(see Factor C below). However, this threat is being monitored and 
managed in all States and the Navajo Nation, and modeling results 
suggest seasonal shooting closures implemented in Colorado and Arizona 
will likely reduce population-level losses. Therefore, we have 
determined that overutilization for commercial, recreational, 
scientific, or educational purposes is not a significant threat to the 
Gunnison's prairie dog.

C. Disease or Predation

    While prairie dogs are prey to numerous species, including coyotes, 
badgers, black-footed ferrets, and various raptor species, there is no 
information available to indicate that predation has an overall adverse 
effect on the species. Black-footed ferrets have been reintroduced into 
two locations in Arizona, including the Aubrey Valley, where Gunnison's 
prairie dog populations appear to be stable.
    The Gunnison's prairie dog is, however, affected by sylvatic 
plague, which occurs in regular outbreaks and causes population 
declines and extirpations. Plague is an exotic disease foreign to the 
evolutionary history of North American species (Barnes 1982, p. 238; 
Barnes 1993, p. 29; Biggins and Kosoy 2001, p. 907). This flea-borne 
disease, caused by infection with the bacterium Yersinia pestis, is 
shared by humans and other vertebrate animals. Rodents are the primary 
vertebrate hosts of Y. pestis, but other mammals can be infected. Y. 
pestis is transmitted to mammals by bites of infected fleas, direct 
contact with infected animals, and rarely by inhalation of infectious 
respiratory droplets from another animal (Gage et al. 1995, pp. 695-
696). Plague was first observed in wild rodents (termed sylvatic 
plague) in North America near San Francisco, California, in 1908 and 
was detected in Gunnison's prairie dogs in the 1930s (Eskey and Hass 
1940, p. 6). Plague has subsequently spread so that it now encompasses 
the entire range of the species (Centers for Disease Control 1998, p. 
1; Cully 1989, p. 49; Girard et al. 2004, p. 8408). Therefore, it has 
only been present within the species' range for approximately 70 years, 
allowing very little time for any resistance to evolve (Biggins and 
Kosoy 2001, p. 913). Once established in an area, plague becomes 
persistent and periodically erupts, with the potential to eventually 
extirpate or nearly extirpate entire colonies (Barnes 1982, p. 255; 
Barnes 1993, p. 28; Cully 1989, p. 51; Cully et al. 1997, p. 711; 
Fitzgerald 1993, pp. 52-53). The term ``enzootic'' describes plague 
existing at a less severe level, sometimes referred to as a 
``maintenance'' condition, that is present continuously throughout a 
species' habitat; the term ``epizootic'' describes a severe plague 
outbreak or amplification transmission cycle (Gage et al. 1995, p. 
696).
    Prairie dogs are highly susceptible to plague, and this 
susceptibility is thought to be a function of high population 
densities, abundant flea vectors, and uniformly low resistance (Biggins 
and Kosoy 2001, p. 913). Gunnison's prairie dogs can experience 
mortality rates of greater than 99 percent during epizootics, and 
eradication of populations can occur within one active season 
(Lechleitner et al. 1962, pp. 190-192; Lechleitner et al. 1968, p. 736; 
Rayor 1985, p. 194; Cully 1989, p. 49).
    Oral vaccination through consumption of vaccine-laden baits could 
reduce mortality from plague. Mencher et al. (2004, pp. 5504-5505) 
report protection against plague in black-tailed prairie dogs, elicited 
through voluntary consumption of a vaccine-laden bait in the 
laboratory. The vaccine has been shown to be safe in numerous animals 
including black-footed ferrets, raccoons, skunks, bobcats, cats, dogs, 
and sheep. However, future field trials are required to test the 
efficacy on the Gunnison's prairie dog.
    Recovery rates of Gunnison's and Utah prairie dog colonies studied 
2 years post-epizootic found that Gunnison's prairie dog colonies 
experienced 100 percent mortality and remained depopulated throughout 
the study due to the lack of available immigrants (Turner 2001, p. 14). 
Partial or complete recovery following population reductions due to 
plague have been reported for both white-tailed and black-tailed 
prairie dogs (Cully 1993, pp. 40-41), but little to no recovery has 
been noted in montane Gunnison's prairie dog colony die-offs, even 
after long periods of time (Capodice and Harrell 2003, pp. 5-7; Cully 
et al. 1997, p. 717; Lechleitner et al. 1968, p. 734). Possible long-
term consequences of continued plague infection in Gunnison's prairie 
dog populations may be:
    (1) local extirpation of colonies;
    (2) reduced colony size;
    (3) increased variance in local population sizes, and
    (4) increased inter-colony distances (CDOW 2007, p. 43).
    The factors that influence interspecific (between species) 
transmission of plague from mammalian or avian reservoirs (for example, 
coyotes, raptors, corvids) into prairie dog populations are unclear, 
but seem to be primarily through fleas that could increase in moister 
climates (Parmenter et al. 1999, p. 818; Rayor 1985, p. 195). However, 
interspecific transmission does not seem to be a significant factor 
creating plague epizootics. Plague is now considered enzootic 
throughout the range of the Gunnison's prairie dog.
    The primary factor influencing plague enzootics in Gunnison's 
prairie dogs is thought to be abundance of fleas within their own 
colonies. This appears to be correlated with seasonal moisture in 
specific habitat areas. Plague outbreaks may be triggered by climatic 
conditions, such as mild winters and moist springs (Parmenter et al. 
1999, p. 818; Rayor 1985, p. 195). Enscore et al. (2002, p. 191) found 
a close relationship between human plague cases in the southwestern 
United States and high amounts of late spring (February to March) 
precipitation (time-lagged 1 and 2 years) and maximum daily summer 
temperature values in the moderately high range (85 to 90 [deg]F; 29 to 
32 [deg]C).
    Girard et al. (2004, p. 8408) postulated that when resistant hosts 
of plague encounter a susceptible species that is plague na[iuml]ve and 
has a high population density, an epizootic occurs. During epizootic 
phases, declines in abundance of susceptible species like prairie dogs 
are observed (Hanson et al. 2007, p. 790). The rapid dispersal of the 
pathogen through an area can be followed by an enzootic phase, a slower 
transmission cycle that disperses through the lower-density, more 
resistant hosts remaining from the first cycle. This establishes the 
disease in stable reservoirs for future emergence

[[Page 6669]]

(Girard et al. 2004, p. 8413; Gage and Kosoy 2005, pp. 506-509).
    Enzootic infection is generally considered characteristic of a 
stable rodent-flea infectious cycle where host rodents are relatively 
resistant to the disease. However, Hanson et al. (2007, p. 792) found 
that an unexpectedly high percentage of black-tailed prairie dog 
colonies in Montana tested positive for plague. They speculate that, 
under some conditions, black-tailed prairie dogs, rather than acting as 
resistant hosts, may serve as enzootic hosts or carriers of the 
pathogen. Plague antibody titers (concentrations in blood) have been 
found in small numbers of Gunnison's prairie dogs in New Mexico, 
indicating individual exposure to plague and subsequent recovery (Cully 
et al. 1997, p. 717; Cully and Williams 2001, p. 898). Plague appears 
to have had little effect on a Gunnison's prairie dog population in 
Aubrey Valley, Arizona (Wagner and Van Andelt 2007, p. 2). However, 
little evidence of resistance to plague has been found in any species 
of prairie dog at this time.
    In conducting a Population Viability Analysis on Gunnison's prairie 
dogs, the IUCN/SSC Conservation Breeding Specialist Group (CDOW 2007, 
p. 123) hypothesized that in an enzootic scenario, plague operates at a 
relatively low level each year, thereby increasing average annual rates 
of mortality above what would occur in a more benign non-enzootic 
scenario.
    Gunnison's prairie dog populations are more susceptible to decline 
from plague than white-tailed prairie dog populations and are at least 
as, if not more, susceptible than black-tailed prairie dog populations 
(Antolin et al. 2002, p. 14; Cully 1989, p. 51; Cully and Williams 
2001, p. 899; Hubbard and Schmitt 1983, p. 51; Knowles 2002, p. 13; 
Ruffner 1980, p. 20; Torres 1973, p. 31; Turner 2001, p. iii). 
Gunnison's prairie dogs commonly forage outside of their home 
territory, a characteristic that may play a significant role in the 
susceptibility of the species to plague. The Gunnison's prairie dog may 
be more susceptible to plague than the black-tailed prairie dog because 
of the Gunnison's less exclusive territorial behavior (many mix 
relatively freely throughout adjacent territories) and thereby 
contribute to the communicability of plague (Hoogland 1999, p. 8).
    The Gunnison's prairie dog is also likely more susceptible to 
plague than the white-tailed prairie dog because the Gunnison's 
typically occurs at higher densities and is less widely dispersed on 
the landscape, allowing for more frequent transmission of the disease 
from one individual to another (Antolin et al. 2002, p. 19; Cully 1989, 
p. 49; Cully and Williams 2001, p. 901; Turner 2001, p. 31). Biggins 
(2003, p. 6) speculated that if transmission rates for plague are at 
least partly dependent on host density, prairie dog populations on good 
quality sites may undergo both larger declines and more rapid 
recoveries than those on poor sites.
    Available literature is inconclusive regarding whether isolation or 
density of a colony affects the number and frequency of plague 
outbreaks. Lomolino et al. (2003, p. 118) and others (Cully and 
Williams 2001, p. 901; Miller et al. 1993, pp. 89-90) suggested that 
isolation and fragmentation may provide some protection to prairie dogs 
from plague by lessening the likelihood of disease transmission. 
However, this theory no longer applies when plague is enzootic 
throughout the range of Gunnison's prairie dog (as it appears to be), 
in which case isolation of colonies reduces the chance of 
recolonization after extirpation (Wagner and Drickamer 2002, p. 16; 
Lomolino and Smith 2001, pp. 942-943). In areas where Gunnison's 
prairie dog colonies are located close to each other (less than 6 miles 
(mi) (10 kilometers (km) apart), inter-colony dispersal of plague is 
likely through infected prairie dogs (Girard et al. 2004, p. 8412). For 
colonies separated by long distances or unsuitable habitats, infection 
may occur due to long-distance dispersal of plague-infected fleas by 
domestic dogs, coyotes, raptors, or other predators and scavengers 
(Barnes 1993, p. 34), or plague may already persist as enzootic 
throughout Gunnison's prairie dog range.
    The impacts of plague outbreaks, which lead to the loss of prairie 
dog colonies of all sizes (Roach et al. 2001, p. 956), are magnified by 
isolation of colonies. Colony growth after an epizootic is mainly the 
result of recolonization by inter-colony dispersers (Antolin et al. 
2002, p. 17). Wagner et al. (2006, pp. 334-335) studied cycles of 
extirpation and recolonization in Gunnison's prairie dogs in Arizona, 
including a large number of colonies over a large geographic area, and 
found a significant relationship between the persistence of colonies 
and the persistence of their nearest neighboring colony. Increased 
isolation decreases the likelihood of recolonization following a plague 
outbreak if the distance between the infected colony and the next 
nearest colony is beyond the dispersal capabilities of the species. For 
example, Lechleitner et al. (1962, pp. 195, 197) documented a 1959 
plague outbreak in a Gunnison's prairie dog colony in Colorado that 
killed all members of the colony. Prior to the outbreak, this colony 
had been continuously occupied for 20 years, despite several poisoning 
attempts. Two years after the plague outbreak, the colony still had not 
been recolonized, likely because it was isolated from other colonies by 
8 mi (13 km) (Lechleitner et al. 1962, p. 187).
    Research is underway on the efficacy of insecticides in protecting 
various prairie dog species from plague. Biggins and Godby (2005, p. 2) 
hypothesized that if enzootic plague is affecting populations of 
prairie dogs, an ambitious effort to remove the disease should result 
in increased survival rates of prairie dogs. Fleas in Utah prairie dog 
burrows were effectively controlled by annual treatments of the 
insecticide deltamethrin; fleas were reduced 96 to 98 percent within 
one month of treatment (Biggins and Godby 2005, p. 5). Studies of the 
effects of flea control on black-tailed and white-tailed prairie dogs 
have shown similar results (Biggins 2007). At this time, chemical 
dusting of individual prairie dog burrows is labor intensive and 
expensive.
    All recent, major Gunnison's prairie dog colony declines documented 
in published literature have been attributed to plague epizootics. 
However, the magnitude of the plague threat appears to be different in 
the montane and prairie portions of the Gunnison's prairie dog range. 
Population declines in prairie habitat are less dramatic than those in 
montane habitat; partial recovery or establishment of new colonies have 
been documented following plague in the prairie range portion, but are 
rare or absent following plague outbreaks in the montane range.
    We reviewed literature on the status of Gunnison's prairie dog 
populations within the two portions of the range and, specifically, all 
published and unpublished literature on the effects of plague on 
prairie dogs. While some studies were not recent, summarizing them 
below provides background on the responses of Gunnison's prairie dog 
populations to plague in each portion of the range.

Effects of Plague in Montane Habitat

    Several well-studied colonies within the montane portion of the 
Gunnison's prairie dog range have been documented as being extirpated, 
or nearly so, due to plague. The South Park, Colorado, population area 
included estimated occupied habitat of 915,000 ac (371,000 ha) in 1945; 
74,000 ac (30,000 ha) in 1948; and 42 ac (17 ha) in 2002 (CDOW

[[Page 6670]]

2007). This decline was largely due to plague and affected a 
substantial portion of the species' extant occupied habitat in Colorado 
(at least 15 percent). A plague event in Saguache County, Colorado, 
that progressed across seven colonies in 2 years left only scattered 
individuals surviving in two colonies (Lechleitner et al. 1968, p. 
734). In Gunnison, Saguache, and Montrose Counties, Colorado, plague 
also was responsible for a decline from 15,569 ac (6,228 ha) of 
occupied habitat in 1980, to 770 ac (308 ha) in 2002 (note that 
Montrose County is in the Southwest population area in prairie habitat) 
(Capodice and Harrell 2003, pp. 5-7). A complete die-off of a colony 
due to plague in Chubbs Park, Chaffee County, Colorado, occurred in 
1959 (Lechleitner et al. 1962, p. 185). In August 1958, the population 
was stable and healthy, but in 1959 an epizootic spread 2 mi (3 km) 
within 3 months; prairie dogs continued to be absent from the area in 
1960 and 1961, and we have no recent information on the existence of 
prairie dogs in that location. Plague resulted in the complete loss, 
over a 2-year period, of a colony in South Park, Colorado (Fitzgerald 
1970, pp. 68-69).
    Approximately 1,000 to 1,500 Gunnison's prairie dogs were killed by 
an outbreak of plague in a 148-ac (60-ha) colony in Curecanti National 
Recreation Area near Gunnison, Colorado, in 1981 (Rayor 1985, p. 194). 
A few animals survived the disease and Gunnison's prairie dogs were 
again abundant in the area in 1986 (Cully 1989, p. 49). In 2002, 252 ac 
(102 ha) of habitat in the Recreation Area were occupied by Gunnison's 
prairie dog colonies (Capodice and Harrell 2003, p. 23), but the 
current estimate is 12 ac (4.8 ha) (Childers 2007, p. 2). Colonies 
within the Recreation Area experienced six plague epidemics between 
1971 and 2007. Of the 9 historic Gunnison's prairie dog colonies, 3 are 
currently active, and 2 act as source populations for the main prairie 
dog concentration area (Childers 2007, p. 1). If the source colonies 
die off due to plague, repopulation may not be possible because any 
other Gunnison's prairie dog populations remaining will be separated by 
distance (more than 6 mi (10 km)) and impassable geographical features 
such as rivers and mountains (Lomolino et al. 2003, p. 116; Pizzimenti 
and Hoffman 1973, p. 1).
    Recently, plague has been implicated in the loss of several large 
colonies on BLM land within the Gunnison population area (CDOW 2007, p. 
4). A large colony southeast of Gunnison, Colorado, that was very 
active in 2005, was totally devoid of prairie dogs in 2006 and 2007. 
Four other large colonies in the same vicinity were active in 2006, but 
by 2007, no prairie dog activity was observed. Plague is the suspected 
cause of these extirpations, because of the complete elimination of the 
prairie dogs with no sign of poisoning (CDOW 2007, p. 4).
    Fitzgerald (1993, p. 52) expressed concern about the status of the 
Gunnison's prairie dog in Colorado, indicating that plague had 
eliminated many populations, including almost all of the populations in 
South Park. He also suggested that populations appeared to be in poor 
condition in the San Luis Valley, and were extirpated from the extreme 
upper Arkansas River Valley, as well as Jefferson, Douglas, and Lake 
Counties. These areas comprise most of the Gunnison's prairie dog 
montane habitat in Colorado.
    During 1984 through 1987, a plague event reduced the population of 
Gunnison's prairie dogs in the Moreno Valley of New Mexico from more 
than 100,000 individuals to between 250 and 500, a decline of greater 
than 99 percent (Cully et al. 1997, pp. 708-711). Although the growth 
rate of the remaining population increased following the epizootic, 
another plague event swept through the area in 1988, and the population 
in July 1996 was still ``a fraction'' of what it had been in 1984 
(Cully et al. 1997, p. 718).
    Occupancy modeling performed in Colorado in 2005 indicated a lower 
proportion of occupancy in the montane portion of the species' range 
within Colorado (3.2 percent) than in the prairie portion within 
Colorado (16.0 percent) (Andelt et al. 2006, p. 17; CDOW 2007, p. 19). 
When the study was repeated over the same plots in 2007, occupancy was 
again found to be lower (3.6 percent) in the montane range portion in 
Colorado than in the prairie portion (18.3 percent) (CDOW 2007, p. 19). 
The only recent threat responsible for whole population declines and 
extirpations, as documented in the studies cited in this section, is 
plague.
    The frequency of plague epizootics appears to be high in montane 
habitat due to moister environmental conditions that are conducive to 
greater flea densities. The impact of plague epizootics in montane 
habitat is great because the small, isolated populations cannot 
recolonize. Within the South Park, Gunnison, and Southeast montane 
population areas in Colorado, no prairie dog complexes that approach a 
size considered sustainable exist, and only a few small complexes exist 
within the San Luis Valley population area (CDOW 2007, pp. 1-17). 
Without a metapopulation structure, an overall decline in persistence 
takes place (Lomolino and Smith 2001, p. 942).
    The landscape status in the montane portion of Gunnison's prairie 
dog range is characterized by fewer, smaller colonies that are 
isolated, and few to no complexes or metapopulation structure. 
Isolation of populations is related to the montane geography in this 
portion of the range. Gunnison's prairie dogs occupy low valleys and 
mountain meadows within this habitat (Seglund et al. 2005, p. 12), 
likely because the short growing season at elevations higher than 
10,000 ft (3,048 m) limits forage (Andelt et al. 2006, p. 17). In 
addition, mountain topography minimizes the zone of contact between 
populations (Knowles 2002, p. 3). At least four mountain ranges within 
the montane portion of the range act as barriers to Gunnison's prairie 
dog dispersal (Pizzimenti and Hoffman 1973, p. 1). These factors make 
the prairie dogs in this habitat highly susceptible to plague-related 
declines, and we have no evidence of long-term recovery from plague in 
the montane habitat area.

Effects of Plague in Prairie Habitat

    The Southwest and the La Plata-Archuleta populations in Colorado 
are within the prairie portion of Gunnison prairie dog range. The 
Southwest population comprises the largest population of Gunnison's 
prairie dogs in Colorado, with an estimated 88,267 ac (35,307 ha) of 
active colonies. Currently, prairie dogs can be found in nearly any 
habitat suitable for occupation, although densities are low to very low 
in native rangeland areas. Plague may be a problem in this area, 
because periodic die-offs not associated with poisoning or other 
control measures have been noted by local farmers and ranchers in the 
past. However, unlike populations in montane habitat within Colorado, 
these populations appear to rebound from periodic epizootics (CDOW 
2007, p. 16).
    Populations in the La Plata-Archuleta population area appear to 
undergo plague outbreaks every 4 to 7 years, which may be limiting some 
populations (CDOW 2007, p. 7). Occupancy modeling in 2005 and 2007 
documented Gunnison's prairie dog occupancy of 17.6 percent and 27.0 
percent, respectively, in the Southern Ute Reservation (part of the La 
Plata-Archuleta population area), and 15.6 percent and 16.3 percent in 
the Southwest area (CDOW 2007, p. 19). The persistence of these 
populations, while undergoing repeated plague outbreaks, is likely due 
to their proximity to other populations within the prairie portion of 
the species' range

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and immigration from those populations.
    In Arizona, from 1987 to 2001, an estimated 68 percent reduction in 
the number of active Gunnison's prairie dog colonies occurred, 
primarily due to outbreaks of plague (Underwood 2007, p. 18; Wagner and 
Drickamer 2002, p. 15). However, in the area known as the Coconino 
Plateau, the area occupied by Gunnison's prairie dogs increased from 
2,126 ac (860 ha) in 1992 to 40,942 ac (16,569 ha) in 2007 (Van Pelt 
2007, p. 3), suggesting the species can withstand large plague 
epizootics through colony expansion or recolonization from nearby 
colonies. In addition, the Aubrey Valley Complex (in northwestern 
Arizona