Endangered and Threatened Wildlife and Plants; 12-Month Finding for a Petition To List the Black-Tailed Prairie Dog as Threatened

AGENCY:

Fish and Wildlife Service, Interior.

ACTION:

Notice of 12-month petition finding.

SUMMARY:

We, the Fish and Wildlife Service, announce a 12-month finding for a petition to list the black-tailed prairie dog (Cynomys ludovicianus) as threatened throughout its range under the Endangered Species Act of 1973, as amended (Act). After reviewing all available scientific and commercial information, we have determined that listing this species is warranted but precluded by other higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants. Upon publication of this notice of 12-month petition finding, the black-tailed prairie dog will be added to our candidate species list.

This decision is based on_the number, variety, and significance of threats affecting the species, especially sylvatic plague (an exotic disease to which the species has no resistance) and inadequate regulatory mechanisms (some areas mandate eradication); evidence of recent general population declines in a significant portion of the species' range; and cumulative rangewide population data indicating overall population declines since 1980.

DATES:

The finding announced in this document was made on February 4, 2000.

ADDRESSES:

You may submit data, information, comments, or questions concerning this finding to the Field Supervisor, U.S. Fish and Wildlife Service, 420 South Garfield, Suite 400, Pierre, South Dakota 57501. You may inspect the petition finding, supporting data, and comments by appointment during normal business hours at the above address. The petition finding also will be available at the Service's Region 6 website at <www.r6.fws.gov/btprairiedog>.

FOR FURTHER INFORMATION CONTACT:

Pete Gober, Field Supervisor, South Dakota Field Office (see ADDRESSES section), telephone (605) 224-8693, extension 24, or facsimile (605) 224-9974.

SUPPLEMENTARY INFORMATION:

Background

On July 31, 1998, we received a petition dated July 30, 1998, from the National Wildlife Federation (National Wildlife Federation 1998). The Petitioner requested that we list the black-tailed prairie dog as threatened throughout its range. The Petitioner also requested that the species be afforded emergency listing. Section 4 of the Act and regulations at 50 CFR 424 do not provide for petitions to request the listing of species on an emergency basis. However, section (4)(b)(7) of the Act and the Service's Listing Priority Guidance (63 FR 25502) direct that all petitions are to be reviewed to determine if an emergency listing is appropriate. We determined and advised the Petitioner by letter dated August 27, 1998, that it would be inappropriate to list this species on an emergency basis given its then known status. On September 16, 1999, the Petitioner requested that we readdress this issue based on reports of increased control efforts (Graber, National Wildlife Federation, in litt. 1999). We have reevaluated information available regarding this subject and determined that emergency listing of the species is not appropriate at this time.

Section 4(b)(3)(A) of the Act requires that, for any petition to revise the List of Threatened and Endangered Species containing substantial scientific and commercial information that listing may be warranted, we make a positive 90-day finding and initiate a status review of the species. We published a notice of a positive 90-day finding on the subject petition in the Federal Register on March 25, 1999 (64 CFR 14425). Accordingly, the subject petition requires a 12-month administrative finding pursuant to section 4(b)(3)(B) on whether the petitioned action is—(I) not warranted, (ii) warranted, or (iii) warranted but precluded from immediate proposal by other higher priority efforts to revise the List of Threatened and Endangered Species. When we find a petition to list a species is warranted but precluded, the species is designated a candidate species.

We believe that sufficient information is currently available to support a finding that listing the black-tailed prairie dog as threatened is warranted, but that a proposed rule at this time is precluded by work on other higher priority listing actions. We will reevaluate the status of the species in 1 year. The information contained in this notice is a summary of the information in the 12-month finding.

The National Wildlife Federation petition presented extensive information regarding the biology of the black-tailed prairie dog. This information included a description of the species and its range, as well as comments related to its population biology and trend. The Petitioner noted that the species still occurs intermittently throughout most of its historic range, although much reduced in numbers and in the amount of habitat that it occupies. The Petitioner contrasted reports that the black-tailed prairie dog once occupied as much as 100-200 million acres (ac) (40-80 million hectares (ha)) of the western North American prairie with current estimates of occupied habitat and concluded that the species' habitat has been reduced by at least 99 percent. The Petitioner attributed reductions in occupied habitat to habitat loss and degradation related to the conversion of prairie grasslands to farmland, extensive control, disease, urban development, unregulated shooting, and other factors.

On August 26, 1998, we received another petition regarding the black-tailed prairie dog from the Biodiversity Legal Foundation, the Predator Project, and Jon C. Sharps (Biodiversity Legal Foundation et al. 1998). They requested that we list the black-tailed prairie dog as threatened throughout its known historic range in the contiguous United States. We accepted this second request as supplemental information to the National Wildlife Federation petition. The Biodiversity Legal Foundation et al. (1998) provided estimates of historic and current distribution of the black-tailed prairie dog, both regionally and by State. They noted that the species' populations are impacted by eradication programs, sylvatic plague, recreational shooting, land conversion, and natural predation. The Biodiversity Legal Foundation (1999) also developed and submitted a potential plan for black-tailed prairie dog conservation.

The notice of a 90-day finding that a petition to list the black-tailed prairie dog presented substantial information that appeared in the Federal Register on March 25, 1999 (64 FR 14424). In this notice, we requested that any additional scientific information relevant to a proposed 12-month administrative finding be submitted to us by May 24, 1999. We published a notice in the Federal Register on June 4, 1999 (64 FR 29983), that reopened this period for an additional 45 days, through July 19, 1999. On October 4, 1999, we again published a notice that we would accept additional information, especially pertaining to a draft black-tailed prairie dog Conservation Assessment and Strategy (Strategy) developed by various States and its effect on the status of the species (64 FR 53655). This information collection period closed November 3, 1999.

We received approximately 14,500 comment letters during the development of this finding. The following summarizes the sources and general content of information we received.

All State wildlife agencies within the historic range of the black-tailed prairie dog provided written comments on the petition. Two State agriculture departments (New Mexico and Wyoming) and two State Legislatures (North Dakota and Wyoming) also provided comments. In general, the States opposed listing the black-tailed prairie dog but supported the development of conservation measures for the species. Most information provided by the States focused on policy and jurisdictional concerns rather than on information related to the biological status of the species.

State wildlife agencies and other interested parties also developed a Strategy for conservation of the black-tailed prairie dog (Van Pelt in prep.). The actions identified in the current draft of this Strategy remain tentative and do not at this time confer any improved status for the species. Eight of the 11 participating State wildlife agencies have signed a Memorandum of Understanding for the purpose of implementing the States' Strategy for the black-tailed prairie dog. At this time, the strategy does not include participation by the States of New Mexico, North Dakota, and Colorado, other State (non-wildlife) agencies, Federal agencies, Tribal agencies, or any private interests. We recognize the significant effort that went into the development of this strategy, and we believe that the strategy is a positive step in addressing the conservation needs of the black-tailed prairie dog. At this early stage in development of the strategy, the document lacks commitments to specific immediate actions that would affect the status of the species. We will continue working with the States and other interested parties to support the coordinated conservation efforts of the States.

Three Tribes in South Dakota provided written comments on the petition—the Cheyenne River Sioux Tribe, the Crow Creek Sioux Tribe, and the Rosebud Sioux Tribe. Information was provided by these Tribes regarding distribution and abundance and existing regulatory mechanisms on and adjoining their respective Tribal lands.

Several Federal agencies provided written comments on the petition. The Bureau of Indian Affairs (BIA) supported conservation measures and acknowledged a possible need to list the species. The U.S. Forest Service provided supplemental information regarding the current status of black-tailed prairie dogs on National Grasslands (Sidle, U.S. Forest Service, in litt. 1999). The National Park Service provided information on its control efforts and noted its preference for the development and implementation of cooperative management strategies among State, Tribal, and Federal agencies rather than a listing of the species. The Corps of Engineers Omaha District also reviewed information provided in the petition, but had no specific comments.

Twenty-three county agencies (county commissions and weed/pest councils) in Colorado, Montana, Nebraska, South Dakota, and Wyoming provided written comments on the petition. All county agencies were opposed to listing the species. Economic considerations were a common concern in these comment letters. Because the Act directs that only biological considerations are to be addressed in the listing process, we cannot address economic considerations in review of this petition.

One hundred forty-four organizations (wildlife/conservation or livestock/land management organizations) provided written comments on the petition. Forty-two wildlife/conservation organizations supported listing of the black-tailed prairie dogs. Eighty-seven livestock/land management organizations were opposed to listing the species. Fifteen organizations provided recommendations but did not indicate a position.

Over 14,300 individuals provided written comments on the petition. Approximately 90 percent of all individuals supported listing the black-tailed prairie dog as threatened. The issues most frequently noted in these letters were impacts from the loss of 99 percent of the species' habitat, recreational shooting, control, and disease. Individuals opposed to listing the species most frequently expressed the view that adequate numbers of the species exist, the species is able to reproduce rapidly in response to adverse impacts, sport shooting does not impact the species, and adverse economic impacts can occur if the species is not controlled.

We received approximately 9,000 letters during the third comment period (October 4 to November 3, 1999). Of these, 84 mentioned the States' Strategy, 25 of which opposed the States' Strategy, mostly due to a perceived lack of specific conservation measures and reliance on future, voluntary actions. Fifty-six letters supported the States' Strategy, most expressing the view that the proposed measures were sufficient to avoid listing and that State management was preferable to Federal management. The remaining 3 of the 84 commenters did not express a position.

Taxonomy

Five species of prairie dogs occur in North America. Prairie dogs are rodents within the squirrel family (Sciuridae) and include the black-tailed prairie dog, the white-tailed prairie dog (Cynomys leucurus), the Gunnison's prairie dog (C. gunnisoni), the Utah prairie dog (C. parvidens), and the Mexican prairie dog (C. mexicanus) (Pizzimenti 1975). The Utah and Mexican prairie dogs are currently listed as threatened (49 FR 22339) and endangered (35 FR 8495), respectively. Generally the black-tailed prairie dog occurs east and north of the other four species in less arid habitat.

Some scientific literature describes a subspecies (Cynomys ludovicianus arizonensis) of the black-tailed prairie dog. This subspecies, found in northeastern Mexico (Ceballos et al. 1993), is extirpated in Arizona (Alexander 1932; Bureau of Sport Fisheries and Wildlife 1961; Van Pelt, Arizona Game and Fish Department, in litt. 1998) and has a remnant population in southwestern New Mexico (Hall and Kelson 1959) and in the Trans-Pecos region of Texas (Davis 1974, Hall and Kelson 1959). A complex of this subspecies in Chihuahua, Mexico, comprises the largest remaining prairie dog complex of any prairie dog species (Ceballos and Pacheco 1997).

The remainder of the species is found in eastern Montana, eastern Wyoming, eastern Colorado, eastern New Mexico, southwestern North Dakota, western and central South Dakota, western and central Nebraska, western and central Kansas, western and central Oklahoma, northwestern Texas, and southwestern Canada. Although some literature describes a subspecies, the research that has focused on evolutionary divergence (genetic segregation and differentiation within a taxon) supports categorizing the black-tailed prairie dog as a monotypic species. Based on this research we do not consider this subspecies separation to be valid. We consider the species as being monotypic. For the remainder of this notice, the use of the common name “black-tailed prairie dog” includes both varieties discussed above.

Biology

Prairie dogs are small, stout ground squirrels. The total length of an adult black-tailed prairie dog is approximately 14-17 inches. The weight of an individual ranges from 1 to 3 pounds. Individual appearances within the species vary in mixed colors of brown, black, gray, and white. The black-tipped tail is characteristic (Hoogland 1995). Black-tailed prairie dogs are diurnal, burrowing animals and spend most of the day above ground. They do not hibernate as do white-tailed, Gunnison's, and Utah prairie dogs (Hoogland 1995, Tileston and Lechleitner 1966). The species is very social, living in population aggregations called colonies, towns, or villages (King 1955). Groups of colonies comprise a complex. Historically, they generally occurred in large colonies that contained thousands of individuals, covered hundreds of thousands of acres, and extended for miles (Bailey 1905). This description is no longer accurate for existing black-tailed prairie dog populations; most colonies are now much smaller.

The colonial behavior of prairie dogs, especially the black-tailed prairie dog, is a significant characteristic of the species. Colonial behavior offers an effective defense mechanism by aiding in the detection of predators and deterring predators through mobbing behavior. It increases reproductive success through cooperative rearing of juveniles and aids parasite removal via shared grooming. However, it also has been noted that this behavior promotes the transmission of disease, which can significantly suppress populations (Olsen 1981, Hoogland 1995).

Several biological factors determine the reproductive potential of the black-tailed prairie dog. Females usually do not breed until their second year and live 3-4 years (Hoogland 1995, King 1955, Knowles and Knowles 1994). Females of the species produce a single litter, usually 4-5 pups, annually (Hoogland 1995, Knowles and Knowles 1994). Prairie dog dispersal is usually limited to approximately 3 miles (5 kilometers) or less, and individuals dispersing from home colonies generally move into an established colony rather than attempting to initiate a new colony (Garrett and Franklin 1988, Hoogland 1995). These limitations could restrict recruitment of animals into small and declining isolated populations and favor the reestablishment of individuals in nearby, recently abandoned colonies over the establishment of new, more distantly located colonies.

Ecology

The extent to which the black-tailed prairie dog is affected by other species, particularly ungulates, is largely unknown. The black-footed ferret (Mustela nigripes), swift fox (Vulpes velox), mountain plover (Charadrius montanus), ferruginous hawk (Buteo regalis), burrowing owl (Athene cunicularia), and numerous other species are dependent upon prairie dogs to varying degrees. Although reports vary as to those species that require prairie dogs for their survival, at least 9 species depend directly on prairie dogs or their activities to some extent, and another 137 species are associated opportunistically (Kotliar et al. 1999). The most obligatory species of this group is the endangered black-footed ferret. Probably no other species has a more clearly documented dependence on another species than does the black-footed ferret on the prairie dog (Anderson et al. 1986, Biggins et al. 1986, Clark 1989, Forrest et al. 1988, Henderson et al. 1974, Hillman 1968, Miller et al. 1996).

Rangewide Distribution

The historic range of the black-tailed prairie dog included portions of 11 States, Canada, and Mexico. Today it occurs from extreme southern Canada to northeastern Mexico and from approximately the 100th meridian west to the Rocky Mountains. The species is currently present in 10 States including Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming. It has been extirpated in Arizona since as early as 1932 (Alexander 1932). We believe that significant range contractions have occurred in the southwestern portion of the species' historic range in Arizona, western New Mexico and western Texas, and in the eastern portion of the species' historic range in Kansas, Nebraska, Oklahoma, South Dakota, and Texas. These range contractions represent approximately 20 percent of the species' original range. Only a few individuals or none remain in these areas. Approximately 37 percent of the species' potential habitat in the United States has been converted to cropland (Black-footed Ferret Recovery Foundation, in litt. 1999). This habitat loss is essentially permanent and not considered a range contraction in the usual sense occurring at the periphery of a species' range. Although the species will occupy abandoned tilled ground, these lands are generally unavailable for use by the species because the land is continuously disturbed and thus the habitat is lost permanently.

Rangewide Abundance

Historically, black-tailed prairie dogs were one of the most conspicuous and characteristic residents of the short-grass and mixed-grass prairies of the United States. Seton (1953) estimated that, in the late 1800s, 5 billion black-tailed prairie dogs existed over their entire range of 600,000 square miles (384 million ac or 155.5 million ha). Miller et al. (1996) and Mulhern and Knowles (1995) provided a range for historic occupied habitat by all species of prairie dogs of 99 million-247 million ac (40 million-100 million ha). Anderson et al. (1986) noted that, as a conservative estimate for the early 1900s, 104 million ac (42 million ha) of rangeland may have been occupied by all species of prairie dogs. Black-tailed prairie dogs had the most extensive range of all the species of prairie dogs and probably occupied more area than all other species combined (Hoogland 1995). Estimates of historic black-tailed prairie dog occupied habitat of approximately 79 million ac (32 million ha) in the United States by the Black-footed Ferret Recovery Foundation (in litt. 1999) and of approximately 111 million ac (45 million ha ) by Knowles (1998) provide a reasonable historic range for black-tailed prairie dog occupied habitat. It is apparent that regardless of which estimate is considered, tens of millions of acres of occupied habitat once existed in the United States.

At present, the black-tailed prairie dog may be found scattered in remnant populations throughout much of the range that it once occupied. A significant portion of existing occupied habitat rangewide occurs in a few large complexes. Approximately 36 percent of the remaining occupied habitat for the species in North America occurs in seven complexes, each larger than 10,000 ac (4,000 ha). We believe that approximately 768,000 ac (311,000 ha) of occupied habitat currently exists rangewide. This estimate is based on the sum of Service estimates from various States, from Canada, and from Mexico, as discussed under the “Statewide Distribution, Trends, and Abundance” section of this document.

Rangewide Trends

Most estimates of prairie dog population trends are not based on numbers of individuals, but on the amount of occupied habitat for the species. The actual number of animals present depends upon the density of animals in that locality. Estimates of black-tailed prairie dog density across the species' range vary seasonally, but range from 2 to 18 individuals per ac (5 to 45 individuals per ha) (Fagerstone and Ramey 1996, Hoogland 1995, King 1955, Koford 1958, Miller 1996). Most prairie dog surveys do not estimate density because of the high effort and cost involved. We believe that a review of various estimates of occupied habitat area provides the best available and most reasonable means of determining population trends for the species.

The U.S. Geological Survey estimated that the black-tailed prairie dog may occupy less than 0.5 percent of its original range and has experienced an estimated 98 percent decline in population abundance throughout North America (Mac et al. 1998). It notes that the amount of occupied habitat has declined from approximately 100 million ac (40.5 million ha) in the late 1800s to less than 1 million ac (0.4 million ha) at present; a decline of over 99 percent. Barko (1997), Fagerstone and Ramey (1996), Knowles (1998), Mulhern and Knowles (1995), and Wuerthner (1997) concluded that a reduction of approximately 94-99 percent in the amount of occupied habitat within this range has occurred since about 1900. State wildlife agencies generally confirm this decline, but some point out that disproportionately more occupied habitat remains in some areas than in others.

Some increases in the amount of occupied habitat in some areas occurred subsequent to the Executive Order banning the use of compound 1080 (a toxicant) in 1972. These increases appear to have been limited in later years by the use of other toxicants such as zinc phosphide, the continuing spread of sylvatic plague, and other factors (Knowles 1998). Moreover, the majority of these increases (approximately 85 percent) occurred in areas (Montana, South Dakota, and Wyoming) where significant impacts due to disease had not yet occurred.

Survey efforts in some areas have noted significant declines in the amount of black-tailed prairie dog occupied habitat over the last few decades. For example, the U.S. Forest Service has mapped black-tailed prairie dog colonies within the Northern Great Plains National Grasslands in North Dakota, South Dakota, Wyoming, and Nebraska. These grasslands, covering approximately 3.7 million ac (1.5 million ha), included a maximum of 86,220 ac (34,890 ha) of black-tailed prairie dog occupied habitat in the 1970s to the 1990s. In 1997, the U.S. Forest Service mapped 39,420 ac (15,965 ha) of occupied habitat in the same areas, indicating a 54 percent decline (U.S. Forest Service 1998). Data provided by the U.S. Forest Service in 1999 confirmed losses in occupied habitat for the National Grasslands with a 58 percent decline from the 1970s to the present (Sidle, U.S. Forest Service, in litt. 1999).

Lockhart (U.S. Fish and Wildlife Service, in litt. 1998) reported that the recovery program for the black-footed ferret has identified large prairie dog complexes potentially useful for reintroduction of the ferret. Both black-tailed and other prairie dog species are considered. One necessary criteria for these sites is that they contain approximately 10,000 ac (4,000 ha) of occupied habitat. In the late 1980s, the Black-footed Ferret Interstate Coordinating Committee identified dozens of potential sites that may have qualified as suitable for ferret recovery. Black-tailed prairie dog populations at these sites appear to have been reduced by as much as 90 percent within the last 15 years. By 1994 only 16 sites were identified, and by 1998 this number was reduced to 10 sites (7 being black-tailed prairie dog sites). Although the overall trend is a large-scale reduction, population increases have been observed at some locales. These declines have occurred largely in the western portion of the species' range and are generally attributed to sylvatic plague. These declines may be representative of the overall population dynamics of the species in many areas. However, populations in some other areas in the eastern portion of the species' range where plague is mostly absent have increased marginally or remained generally constant during the same period.

Approximately 66 percent, or 300 million ac (122 million ha), of the black-tailed prairie dog range in the United States is affected by sylvatic plague (Black-footed Ferret Recovery Foundation, in litt. 1999). This area includes the western portions of the species' range. Another important factor that has affected the species is the conversion of rangeland to cropland, especially in the eastern portion of the species' range. Conversion of native prairie to cropland has largely progressed across the species' range from east to west with more cropland occurring in the eastern portion of the species' range. In the plague-free portion of the species' range, less than 33 percent of the species' historic range is available to the species (Black-footed Ferret Recovery Foundation, in litt. 1999). Therefore, only approximately 10 percent of the black-tailed prairie dog historic range is both plague-free and available (not cropland) to the species. The majority of plague-free, suitable range occurs in South Dakota.

Statewide Distribution, Abundance, and Trends

In some parts of the species' range, statewide population increases were noted after 1972. However, in most western States, populations have declined since the 1980s, most likely due to sylvatic plague. In the eastern part of the range, where plague has not yet occurred, similar declines have not been observed. These trends are discussed below by State. We have evaluated all historic and current data and information available on the species' abundance and trends. Several estimates of black-tailed prairie dog occupied habitat were available for each State. The dates, methodologies, and ultimately the reliability of these estimates varied. Generally, our estimate of current occupied habitat for each State is the most recently reported estimate with the most reliable methodology (Arizona, Montana, Nebraska, North Dakota, Oklahoma, South Dakota, Canada, and Mexico). For States where a range (Wyoming) or two reliable estimates were available (Kansas), we used the midpoint. For States where no recent estimate with adequate methodology was available (Colorado, New Mexico, and Texas), we extrapolated from older estimates. We rounded all our estimates to the nearest 1,000 ac.

In Arizona, black-tailed prairie dogs existed in the southeastern portion of the State prior to eradication efforts (Hall and Kelson 1959). The species is extirpated at present in the State. Approximately 2 percent of occupied habitat in the United States may have existed in Arizona historically. We believe that intensive grazing at the turn of the last century may have caused occupied habitat to expand in Arizona and that control may have been the principal factor that subsequently suppressed populations. Shrub invasion also may have limited recovery. The species largely disappeared from the State prior to the documented occurrence of sylvatic plague in the State (Shroufe, Arizona Game and Fish Department, in litt. 1999). However, plague is an additional factor that could affect the future viability of the species in Arizona.

In Colorado, black-tailed prairie dogs historically occurred on suitable habitat east of the Rocky Mountain foothills (Hall and Kelson 1959, Torres 1973). Presently, the species appears to be scattered in remnant populations throughout the same area. Statewide estimates of occupied habitat noted for Colorado range from 7 million ac (2.8 million ha) historically to 44,000 ac (18,000 ha) in 1998 (Knowles 1998).

We believe that occupied habitat in Colorado has declined significantly from historic estimates. There is a large disparity in recent statewide estimates of remnant occupied habitat. However, we believe that trends at specific locations within the State (a 50 percent decline in Denver Metropolitan Area from 1994 to 1998 (Seery, U.S. Fish and Wildlife Service, pers. comm. 1998), a 70 percent decline at Rocky Mountain Arsenal National Wildlife Refuge from 1988-1999 (Seery and Matiatos, in press), and a 90 percent decline at Comanche National Grasslands from 1995 to 1998 (Cully 1998), indicate that there has likely been a statewide decline in recent years (despite periodic limited recovery) and that these declines may continue. These declines have largely been attributed to sylvatic plague. We estimate that 93,000 ac (43,000 ha) of black-tailed prairie dog occupied habitat currently exist statewide.

In Kansas, black-tailed prairie dogs historically occurred on suitable habitat throughout the western two-thirds of the State (Hall and Kelson 1959, Smith 1958). Presently, the species appears to be scattered throughout generally the same area, except that the eastern limit of the range appears to have shifted westward approximately 30-50 miles (50-80 kilometers) (Vanderhoof and Robel 1992). Statewide estimates of occupied habitat for Kansas range from 2.5 million ac (1 million ha) historically to 36,000 ac (15,000 ha) in 1998 (Knowles 1998). We estimate that 42,000 ac (17,000 ha) of black-tailed prairie dog occupied habitat currently exist statewide.

We believe that occupied habitat in Kansas has declined significantly from historic estimates, but has likely been stable to slightly declining in recent years. The most recent statewide survey is from 1992 (Vanderhoof and Robel 1992). However, in 1996 sylvatic plague was documented in Kansas on the Cimarron National Grasslands (Cully, U.S. Geological Survey, Biological Resources Division, pers. comm. 1998). Therefore, occupied habitat may decline if sylvatic plague impacts continue and/or spread to other areas of the State.

In Montana, black-tailed prairie dogs historically occurred on suitable habitat in the eastern two-thirds of the State (Flath and Clark 1986), with the exception of the northeastern corner of the State (Hall and Kelson 1959). One of the seven large remaining black-tailed prairie dog complexes occurs in Montana. Statewide estimates of occupied habitat for Montana range from 6 million ac (2.4 million ha) historically (Knowles 1998) to 28,286 ac (11,456 ha) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The Montana Department of Fish, Wildlife, and Parks believes that historic estimates are inaccurate (Graham, Montana Department of Fish, Wildlife, and Parks, in litt. 1998). The most recent estimate of occupied habitat is 66,000 ac (26,000 ha) (Montana Department of Fish, Wildlife and Parks in prep.). We estimate that 65,000 ac (26,000 ha) of black-tailed prairie dog occupied habitat currently exist statewide.

We believe that occupied habitat in Montana has declined significantly from historic estimates. Following a major reduction in occupied habitat from approximately 1900 to 1961, black-tailed prairie dog populations in the State apparently expanded from 1961 to 1986 and then experienced significant declines due to sylvatic plague. The Montana Department of Fish, Wildlife, and Parks (1998) noted that occupied habitat declined by approximately 50 percent from the estimates of the late 1980s, largely due to sylvatic plague.

In Nebraska, black-tailed prairie dogs historically occurred on suitable habitat throughout most of the State west of the 97th meridian (Hall and Kelson 1959, Knowles 1995). Presently, the species appears to be scattered throughout the same area, but at much reduced numbers, especially east of the 99th meridian. Statewide estimates of occupied habitat noted for Nebraska range from 6 million ac (2.4 million ha) historically (Knowles 1998) to 30,000 ac (12,000 ha) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The most recent estimate of occupied habitat is 60,000 ac (24,000 ha) (Knowles 1998). We estimate that 60,000 ac (24,000 ha) of black-tailed prairie dog occupied habitat currently exist statewide.

We believe that occupied habitat in Nebraska has declined significantly from historic estimates and has likely been stable to slightly declining in recent years (Amack, Nebraska Game and Parks Commission, in litt. 1999). This stability may be due to the fact that sylvatic plague does not appear to be widespread in the State, although it has been documented in the northwestern portion of the State where it has impacted some black-tailed prairie dog populations (Virchow et al. 1992).

In New Mexico, black-tailed prairie dogs historically occurred on suitable habitat throughout the southern and eastern two-thirds of the State (Bailey 1932, Hall and Kelson 1959). Presently, the species appears to exist in remnant populations in scattered locations, generally east of the Pecos River (Findley et al. 1975). Statewide estimates of occupied habitat noted for New Mexico range from over 6,640,000 ac (2,690,000 ha) historically (Bailey 1932) to 15,000 ac (6,000 ha) in 1998 (Knowles 1998). We estimate that 39,000 ac (16,000 ha) of black-tailed prairie dog occupied habitat currently exist statewide.

We believe that occupied habitat in New Mexico has declined significantly from historic estimates. Following the toxicant ban in 1972, increases in occupied habitat appear to have occurred. However, declines in occupied habitat have likely occurred in more recent years (Maracchini, New Mexico Department of Game and Fish, in litt. 1998).

In North Dakota, black-tailed prairie dogs historically occurred on suitable habitat in the southwestern third of the State, west of the Missouri River (Hall and Kelson 1959). Presently, the species appears to be scattered throughout the same area. Statewide estimates of occupied habitat for North Dakota range from 2 million ac (810,000 ha) historically (Knowles 1998) to approximately 7,000 ac (2,800 ha) as a conservative estimate in 1973 (Grondahl 1973). The most recent estimate of occupied habitat is a preliminary estimate of approximately 25,000 ac (10,000 ha), based on aerial surveys (Sidle, U.S. Forest Service, pers. comm. 1999). We estimate that 25,000 ac (10,000 ha) of black-tailed prairie dog occupied habitat currently exist Statewide.

We believe that occupied habitat in North Dakota has declined significantly from historic estimates, but has likely been fairly stable to increasing (McKenna, North Dakota Game and Fish Department, in litt. 1999) in recent years. The amount of occupied habitat in North Dakota is relatively small compared to other States in the northern Great Plains.

In Oklahoma, black-tailed prairie dogs historically occurred on suitable habitat in the western two-thirds of the State (Hall and Kelson 1959). Presently, the species is largely limited to the panhandle (Shaw et al. 1993, Tyler 1968, Wuerthner 1997), although scattered remnant populations occur in the western half of the State outside of the panhandle (Shackford et al. 1990). Statewide estimates of occupied habitat noted for Oklahoma range from 950,000 ac (385,000 ha) historically (Knowles 1998) to less than 8,600 ac (3,500 ha) in 1998 (Lomolino, University of Oklahoma, in litt. 1999). We estimate that 9,000 ac (3,600 ha) of black-tailed prairie dog occupied habitat currently exist Statewide.

Populations in the panhandle have experienced significant declines in the past 10 years, although with limited recovery (Lomolino, University of Oklahoma, in litt. 1999). These declines were likely due to plague. The amount of occupied habitat in the remainder of the State has experienced a slow, steady decline (Shackford et al. 1990). Statewide, populations have been reduced by 50 percent in the last 10 years (Lomolino, in litt. 1999).

In South Dakota, black-tailed prairie dogs historically were found throughout all but the eastern one-fourth of the State (Hall and Kelson 1959, Linder et al. 1972). Presently the species appears to be scattered throughout the same area, with the majority of occupied habitat on Tribal or Federal lands west of the Missouri River and small scattered populations elsewhere. Four of the seven remaining large black-tailed prairie dog complexes occur in South Dakota. Statewide estimates of occupied habitat for South Dakota range from more than 1,757,000 ac (712,000 ha) historically, following the initiation of intensive control efforts in 1918 (Linder et al. 1972), to 33,000 ac (13,000 ha) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The most recent estimate of occupied habitat in the State is a preliminary estimate of 147,000 ac (60,000 ha), based on aerial surveys (Sidle, U.S. Forest Service, pers. comm. 1999). We estimate that 147,000 ac (60,000 ha) of black-tailed prairie dog occupied habitat currently exist Statewide.

We believe that occupied habitat in South Dakota has declined significantly from historic estimates, with notable recovery from 1961-1980 (Bureau of Sport Fisheries and Wildlife 1961, Tschetter 1988). Thereafter, extensive control efforts at Pine Ridge Reservation and elsewhere in the 1980s resulted in a significant decline in occupied habitat. Subsequently, occupied habitat has remained fairly stable. More unoccupied, but available, habitat appears to remain in South Dakota than in other States.

In Texas, black-tailed prairie dogs historically occurred on suitable habitat throughout the northwestern one-third of the State (Bailey 1905, Hall and Kelson 1959). Presently, the species occurs largely in the western portion of the panhandle. Some scattered remnant populations exist in the Trans-Pecos Region of western Texas. Statewide estimates of occupied habitat range from 58 million ac (23 million ha) historically to 23,000 ac (9,000 ha ) in 1998 (Knowles 1998). We estimate that 71,000 ac (29,000 ha) of black-tailed prairie dog occupied habitat currently exist Statewide.

We believe that occupied habitat in Texas has declined significantly from historic estimates. However, based upon the limited amount of information available, we believe that occupied habitat increased following the toxicant ban in 1972 and that populations may have remained fairly stable since the late 1970s (Cheatheam 1977, Lair and Mecham 1991).

In Wyoming, black-tailed prairie dogs historically occurred on suitable habitat east of the Rocky Mountain foothills (Clark 1973, Hall and Kelson 1959) below approximately 5,500 feet (1,676 meters) elevation (Van Pelt in prep.). Presently, the species appears to be scattered throughout the same area. One of the seven remaining large black-tailed prairie dog complexes occurs in Wyoming. Statewide estimates of occupied habitat for Wyoming range from 16 million ac (6.5 million ha) historically (Knowles 1998) to 49,000 ac (20,000 ha) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The most recent estimate is 70,000-180,000 ac (28,000-73,000 ha) in 1998 (Knowles 1998). We estimate that 125,000 ac (51,000 ha) of black-tailed prairie dog occupied habitat currently exist Statewide.

We believe that occupied habitat in Wyoming has declined significantly from historic estimates. Increases in occupied habitat occurred following the toxicant ban in 1972. However, we believe that recent declines, largely due to impacts from sylvatic plague, are likely to continue.

Canada Distribution, Abundance, and Trends

Historically, black-tailed prairie dogs occurred on suitable habitat in southernmost Saskatchewan (Hall and Kelson 1959). Presently the species is found in a small area along the Frenchman River Valley. Many of these colonies are in Canada's Grasslands National Park (Laing 1986). Canada represents a very small percentage (approximately 0.3 percent) of the rangewide population. Estimates of occupied habitat in Canada range from 1,244 ac (503 ha) in 1970 (Millson 1976) to 2,318 ac (938 ha) in 1996 (Fargey, Grasslands National Park, pers. comm. 1998). We estimate that 2,000 ac (800 ha) of black-tailed prairie dog occupied habitat currently exists in Canada.

We believe that occupied habitat in Canada has remained at approximately 2,000 ac (800 ha) and, in the absence of sylvatic plague, will likely remain stable.

Mexico Distribution, Abundance, and Trends

Historically, black-tailed prairie dogs occurred on suitable habitat throughout the northern portion of the Mexican States of Chihuahua and Sonora (Hall and Kelson 1959). Presently, most individuals appear to be limited to a small region in northern Chihuahua. The largest remaining black-tailed prairie dog complex occurs in Mexico. Estimates of occupied habitat in Mexico range from 1,384,000 ac (560,000 ha) historically (Mearns 1907 as cited in Ceballos et al. 1993) to 90,000 ac (36,000 ha) in 1996 (List et al. 1997). We believe that the List et al. (1997) estimate of 90,000 ac (36,000 ha) of currently existing black-tailed prairie dog occupied habitat in Mexico is accurate.

We believe that occupied habitat in Mexico has declined significantly from historic estimates and that this decline continues. Decline appears to be due primarily to cropland conversion. From 1988 to 1996, the geographic range of the species in Mexico contracted 80 percent and the amount of occupied habitat decreased by 34 percent (List et al. 1997). Colony fragmentation has occurred in previously surveyed black-tailed prairie dog colonies, reducing the size of towns and increasing their isolation.

Summary of Factors Affecting the Species

Section 4 of the Act and regulations (50 CFR part 424) promulgated to implement the listing provisions of the Act set forth the procedures for adding species to the Federal lists. A species may be determined to be an endangered or threatened species due to one or more of the five factors described in section 4(a)(1). These factors and their application to the black-tailed prairie dog are as follows:

A. The Present or Threatened Destruction, Modification, or Curtailment of the Species' Habitat or Range

We believe that habitat loss due to cropland conversion, urbanization, habitat modification, and fragmentation is a factor adversely affecting black-tailed prairie dog populations rangewide.

In the United States, approximately 37 percent of the suitable habitat within the range of the black-tailed prairie dog has been converted to cropland (Black-footed Ferret Recovery Foundation, in litt. 1999). This land use change resulted in significant destruction of black-tailed prairie dog habitat, particularly in eastern portions of the species' range where adequate precipitation favors farming. Cropland conversion continues, but the amount of occupied habitat converted annually is unknown. In some areas cropland conversion occurs due to continuing improvements in intensive agricultural techniques, for example, dryland wheat farming in Montana (Knowles et al. 1996, Lessica 1995) and irrigated croplands in Mexico (List et al. 1997). List et al. (1997) reported that occupied habitat in Mexico declined by 34 percent between 1988 and 1996, in part due to conversion to cropland.

Habitat loss also has occurred due to urbanization. One example of the present and threatened destruction of black-tailed prairie dog occupied habitat due to urban development is apparent along the Front Range of Colorado near Denver. In 1994, 42,500 ac (17,200 ha) of occupied habitat were mapped in the Denver/Boulder/Fort Collins metropolitan area (Skiba, Colorado Division of Wildlife, pers. comm. 1999). Knowles (1998) estimated that occupied habitat has declined by approximately 8,000 ac (3,200 ha) since the initial mapping effort, due to urbanization. An evaluation of the specific impact of urbanization is difficult because sylvatic plague also has significantly affected populations in this area in recent years (Weber, Colorado Division of Wildlife, pers. comm. 1998).

Habitat modification and loss due to the absence of black-tailed prairie dogs can be anticipated in the prairie ecosystem where populations have been extirpated or significantly reduced in number. Weltzin et al. (1997) determined that black-tailed prairie dogs, and the herbivores and granivores associated with their colonies, probably maintained grassland and savanna historically by preventing woody species such as mesquite from establishing or attaining dominance. List et al. (1997) reported that control of black-tailed prairie dogs in Mexico resulted in the invasion of mesquite shrubs that rendered the landscape unsuitable for reoccupation by the species. Davis (1974) also noted that the removal of the species from some sites in Texas resulted in the invasion of brush. The fragmented nature of remaining prairie dog colonies, barriers to immigration and emigration, and the lack of fire and native ungulate herds that historically denuded the landscape and provided opportunities for prairie dog colonies to expand (Miller et al. 1994) accentuate habitat loss due to vegetative succession. The degree to which this type of grassland change and other landscape alterations affect black-tailed prairie dog populations across their range is unknown. Nevertheless, these subtle habitat changes may be a major factor in precluding the utilization of habitat or recolonization of former habitat by the species.

North American grasslands have suffered among the most extensive fragmentation and transformation of any biome on the continent (Groombridge 1992). More fragmented, more isolated, and less connected populations usually have higher extinction rates (Clark 1989, Gilpin and Soule 1986, MacArthur and Wilson 1967, Shaffer 1981, Wilcove et al. 1986, Wilcox and Murphy 1985). List et al. (1997) suggested that fragmented black-tailed prairie dog colonies in Mexico were prone to extirpation. Miller et al. (1996) described existing prairie dog populations as small, disjunct, and geographically isolated. Dispersal has been limited by barriers created by human development that preclude immigration or emigration. Fragmentation and extirpation of small, isolated colonies will result in the loss of additional genotypes, as occurred with the complete extirpation of the species in portions of the eastern and southwestern areas of its historic range. Lost genetic diversity will inherently be detrimental to the long-term survival of the species.

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

We believe that overutilization of the black-tailed prairie dog via the pet trade is not a significant factor affecting black-tailed prairie dog populations rangewide. Herron (Texas Parks and Wildlife Department, pers. comm. 1999) and others have reported that black-tailed prairie dogs are removed from the wild for sale as pets. Herron was aware of 3 commercial operators who collectively removed approximately 5,000 individuals from the Texas panhandle and other States annually in recent years. Miscellaneous reports indicate that this practice occurs elsewhere in the species' range, but the extent of removal of individuals from the wild for use as pets is unknown.

Recreational (sport or varmint) shooting is impacting black-tailed prairie dog populations in some local areas. At present, we do not believe that this factor is responsible for significant rangewide declines in the species' population; however, it may be important locally. The popularity of shooting has increased appreciably in recent years. Many States do not require hunting licenses and have no bag limits or seasonal restrictions for taking prairie dogs. Some areas administered by the Bureau of Land Management and the U. S. Forest Service have been closed to recreational shooting over the past two years, but recreational shooting is still allowed on other areas administered by these agencies. Recreational shooting is not allowed on on lands administered by the National Park Service or the Fish and Wildlife Service. Knowles (1988) reported that shooting on two black-tailed prairie dog colonies removed 69 percent of the adults. He thought that the reduction of prairie dog populations below a certain threshold number might have a further negative consequence because fewer prairie dogs were available to watch for predators and keep the vegetation clipped around burrows to improve detection of predators. Vosburgh (1996) reported that intensive shooting can have a statistically significant impact on the density of local black-tailed prairie dog colonies. He observed that during the summer, species density declined 33 percent on colonies with shooting and 15 percent on colonies without shooting. Prairie dogs also spent more time in alert postures and less time foraging on colonies where shooting occurred.

Large, healthy populations appear to be able to withstand considerable removal by shooting and remain viable (Bourland and Dupris, Cheyenne River Sioux Tribe, in litt. 1998; Finnegan et al., Rosebud Sioux Tribe, in litt. 1998). Accordingly, the shooting of hundreds of thousands of individuals across the extensive range of the black-tailed prairie dog where millions of individuals occur will not likely adversely impact the overall population of a species where each female can produce an average of four young annually. Conversely, small local populations already depressed by disease and other adverse influences may suffer additive losses from shooting impacts. Shooting impacts also may contribute to population fragmentation and preclude or delay recovery of colonies reduced by other factors, such as sylvatic plague.

C. Disease or Predation

We believe that sylvatic plague is likely the most important factor in recent reductions of many black-tailed prairie dog populations throughout a significant portion of the range of the species. Approximately 66 percent of the species' range has been affected by plague (Black-footed Ferret Recovery Foundation, in litt. 1999). Plague is an exotic disease foreign to the evolutionary history of North American species (Gage, Center for Disease Control, pers. comm. 1999). Plague was first observed in wild rodents in North America near San Francisco, California, in 1908 (Eskey and Haas 1940). It spread eastward across the continent in subsequent years and still appears to be expanding its range, although not as rapidly as in its early years. The first reported incidences of plague in black-tailed prairie dogs occurred in the 1940s (Gage, Center for Disease Control, pers. comm. 1999, Miles et al. 1952). Black-tailed prairie dogs show neither effective antibodies nor immunity to the disease. This disease is caused by the bacterium Yersinia pestis, which fleas acquire from biting infected rodents and other species and then transmit via a bite. Plague also can be transmitted directly between animals. Cully (1989) summarized plague reports in 76 species of 5 mammalian orders in the United States, although plague is primarily a rodent disease. It can seriously affect humans, although it responds well to modern treatment (Center for Disease Control 1997). Rodent species vary in their susceptibility to plague, with some species acting as hosts or carriers of the disease or infected fleas and showing little or no symptoms. Black-tailed and Gunnison's prairie dog populations demonstrate nearly 100 percent mortality when exposed to plague (Barnes 1993, Cully 1993) and cannot be considered carriers.

Plague, once established in an area, becomes persistent and periodically erupts, with the potential to extirpate local black-tailed prairie dog populations. After several epizootics (an eruption of the disease that attacks a large number of animals at the same time), black-tailed prairie dogs at the Rocky Mountain Arsenal National Wildlife Refuge have neared extirpation (Seery, U.S. Fish and Wildlife Service, pers. comm. 1998). This phenomenon may be occurring at other formerly large black-tailed prairie dog complexes across much of the western portion of the species' range. At Northern Cheyenne Reservation in southeastern Montana, a plague epizootic started in 1991 and continued through 1996 (Young 1997), removing 97 percent of the black-tailed prairie dog population (Fourstar, Bureau of Indian Affairs, pers. comm. 1998). The population has begun to recover and has increased from a low of 378 ac (153 ha) of occupied habitat to 963 ac (390 ha). However, Young (University of Arizona, pers. comm. 1998) does not believe that this complex will recover to its former status. The effects of plague on prairie dogs may be exacerbated in smaller, isolated colonies where populations are not buffered by large numbers (where some individuals may escape infection by chance) and where recovery may be hampered by limited immigration from other colonies.

We believe that predation is not likely a major factor affecting overall black-tailed prairie dog populations, but it may be important locally or contribute to the effects of other factors. Little information is available to quantify the impact of predators on prairie dog populations.

D. The Inadequacy of Existing Regulatory Mechanisms

We believe that inadequate regulatory mechanisms are a contributing factor affecting overall black-tailed prairie dog populations. Many States, Tribes, and Federal agencies recognize the historic decline and ecological significance of the black-tailed prairie dog, but few use available regulatory mechanisms to conserve the species. At least one government entity in most States promotes their reduction. However, some limited regulatory mechanisms exist for conservation of the species.

States

In Arizona, the Game and Fish Department classifies all prairie dogs native to the State as nongame mammals. Although the species has been extirpated in Arizona, a hunting season was open until 1999, when it was closed (Shroufe, Arizona Game and Fish Department, in litt. 1999). Arizona does not require the eradication of prairie dogs for agricultural purposes or promote recreational shooting of prairie dogs (Shroufe, Arizona Game and Fish Department, in litt. 1998). The black-tailed prairie dog is listed as endangered on the Arizona Game and Fish Department “Threatened Native Wildlife” list (Arizona Game and Fish Department 1988).

In Colorado, the Division of Wildlife requires a resident or nonresident hunting license for prairie dog shooting unless the animals are on land owned by the shooter. The season is year-round, with no bag or possession limit. However, for hunt contests, no participant may take more than five prairie dogs during the contest. In 1999, the Colorado State Legislature passed a bill prohibiting the translocation of prairie dogs and other species into a county without the consent of the county's commissioners (Van Pelt in prep.).

The State of Kansas considers black-tailed prairie dogs as agricultural pests and mandates control if an adjoining landowner files a complaint (Knowles 1995). In recent years, some counties have invoked “Home Rule” to take over authority for prairie dog control from the townships and impose mandatory control requirements on landowners. The landowner is given the opportunity to control prairie dogs on his land and if he fails to do so it is done by the county at the landowner's expense (Van Pelt in prep.). Shooting of prairie dogs in Kansas is somewhat restricted since a resident or nonresident hunting license is required and established methods of take are listed (Williams, Kansas Department of Wildlife and Parks, in litt. 1998).

In Montana, the Department of Fish, Wildlife, and Parks requires no license to shoot prairie dogs, and no limits on take or season exist. Prairie dogs are protected on two State parks as important features of those parks (Graham, Montana Department of Fish, Wildlife and Parks, in litt. 1998). The Department of Fish, Wildlife, and Parks identifies the black-tailed prairie dog as a State “species of special concern” (Flath 1998). The Department of Fish, Wildlife, and Parks is developing a species conservation plan for black- and white-tailed prairie dogs in Montana (Montana Department of Fish, Wildlife and Parks in prep.). However, the Montana Department of Agriculture classifies prairie dogs as “rodents” and “vertebrate pests.” The Montana Department of Agriculture assists landowners in control of prairie dogs if requested, but such assistance is not mandated (Sullins, Montana Department of Agriculture, pers. comm. 1999).

In Nebraska, the Game and Parks Commission currently considers the black-tailed prairie dog an unprotected nongame species that can be taken in any manner, without restrictions on shooting or control activities. Permits are not required for residents; nonresidents must have a small-game hunting permit. The Game and Parks Commission recognizes prairie dog shooting as an acceptable recreational activity, but suggests that shooting be avoided when prairie dogs have dependent young and that shooters take responsible measures to avoid disturbance of other wildlife species that use prairie dog colonies (Amack, Nebraska Game and Parks Commission, in litt. 1998).

In New Mexico, the Department of Game and Fish requires a license to shoot prairie dogs, but there are no bag limits or restrictions (Knowles 1998). The Petitioner reports that New Mexico considers the prairie dog as a “rodent pest” and mandates that landowners destroy prairie dogs on notice (National Wildlife Federation 1998).

In North Dakota, the Game and Fish Department classifies the black-tailed prairie dog as a nongame wildlife species. A resident is not required to purchase a hunting license to shoot prairie dogs; however, nonresidents are required to purchase one. The State sets no bag limits or seasons for prairie dogs. The North Dakota Game and Fish Department has published a guidebook to aid prairie dog shooters in finding colonies (North Dakota Game and Fish Department undated). The State of North Dakota considers the black-tailed prairie dog a pest, although the Game and Fish Department considers it a nongame species. The North Dakota Department of Agriculture and the county weed boards have regulatory authority over control efforts (Van Pelt in prep.).

In Oklahoma, the Department of Wildlife Conservation classifies the black-tailed prairie dog as a Category II Mammal Species of Special Concern. Prairie dog eradication is no longer mandatory in Oklahoma but is assisted by some State agencies and local governments. Control and recreational shooting of the species can occur on private land, but the Department of Wildlife Conservation does not promote either activity (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1998). A license for recreational shooting is required by residents and nonresidents. The Department of Wildlife Conservation requires that a permit be obtained prior to any control. Prairie dogs cannot be reduced in any county to fewer than 1,000 individuals, and control is not permitted on public lands (Van Pelt in prep.).

In South Dakota, the Department of Game, Fish, and Parks classifies the black-tailed prairie dog as a predator/varmint and requires that a resident or nonresident acquire a license to shoot prairie dogs. No seasons or bag limits have been established. The South Dakota Weed and Pest Control Statute designates the species as a statewide declared pest. Therefore, the existence of prairie dogs constitutes an infestation, giving the State authority to enter private land and exterminate the animals. If a county declares an infestation, landowners are responsible for the costs to control prairie dogs on their land whether they want control or not (Van Pelt in prep.).

In Texas, the Parks and Wildlife Department designates black-tailed prairie dogs as a nongame species and is prohibited by State statute from listing them as a State endangered species. A license is required to hunt prairie dogs, but no season or bag limits have been established. In 1999, the State established a regulation that requires a nongame collection or dealer's permit to possess more than 10 live prairie dogs or to sell prairie dogs (Van Pelt in prep.). This law does not regulate the killing of prairie dogs for recreational, agricultural, or nuisance purposes (Sansom, Texas Parks and Wildlife Department, in litt. 1998). The Texas Health and Safety Code authorizes counties to control prairie dogs and gives the Texas Department of Agriculture responsibility for providing information regarding control to requesting counties (Van Pelt in prep.).

The Wyoming Game and Fish Department regards the black-tailed prairie dog as a nongame wildlife species and has listed it as a Species of Special Concern. No license is required to hunt prairie dogs, and no seasons, bag limits, or restrictions on method of take have been established (Van Pelt in prep.). The Game and Fish Department supports development of seasons and bag limits for the black-tailed prairie dog (Wichers, Wyoming Game and Fish Department, in litt. 1998). The Wyoming Department of Agriculture lists the species as a pest. The Wyoming Weed and Pest Control Act of 1973 authorizes counties to enter private property to control prairie dogs if damage has been documented to neighboring landowners (Knowles 1995).

Tribal

Mulhern and Knowles (1995) estimated that 30 percent of black-tailed prairie dog colonies occur on Tribal lands. Four of the seven remaining large complexes (those with 10,000 acres or more) (Cheyenne River, Fort Belknap, Pine Ridge, and Rosebud) occur on Tribal lands. Two Tribes (Cheyenne River Sioux Tribe in South Dakota and Fort Belknap in Montana) have prairie dog management plans in place (Knowles 1995). No extensive control of prairie dogs has occurred on Cheyenne River Sioux Tribe, Fort Belknap, or Rosebud Sioux Tribe (in South Dakota) in recent years due to concerns related to the conservation of black-footed ferrets. However, active recreational shooting programs on these and other Tribal lands exist. The Cheyenne River Sioux Tribe does not classify the prairie dog as a pest and does not require or encourage their eradication; however, shooting of black-tailed prairie dogs occurs year-round and without limits (Bourland and Dupris, Cheyenne River Sioux Tribe, in litt. 1998). Recreational shooting is also allowed on the Crow Creek Sioux Tribe in South Dakota, but chemical control is not allowed. The Tribe states that shooting appears to have no effect on black-tailed prairie dog numbers, and they report the species as abundant (Miller, Crow Creek Sioux Tribe, in litt. 1998). In 1998, the Rosebud Sioux Tribe Department of Natural Resources implemented a new licensing system for black-tailed prairie dogs in an attempt to reduce the number of shooters. License sales were reduced by approximately 50 percent from approximately 4,000 licenses in 1997 to 2,000 licenses in 1998 (Finnegan, Rosebud Sioux Tribe, pers. comm. 1999).

Federal Agencies

The BIA has a trust responsibility to oversee management of Tribal lands. The BIA's involvement in prairie dog control efforts has been principally through management of funding for prairie dog control programs on Tribal lands. In the northern Great Plains, from 1978-1992, BIA funding was responsible for the control of more prairie dog habitat than any other Federal agency in the country (Roemer and Forrest 1996).

The Bureau of Land Management (BLM) manages prairie dogs to meet multiple-use resource objectives including production of livestock forage and preventing prairie dog movement to adjacent State or private lands. Although BLM no longer actively conducts control, it still allows control to occur by other agencies on its lands and it still allows significant levels of unregulated sport shooting (Knowles 1995). In a memorandum dated June 23, 1999, and expiring September 30, 2000, the BLM instructed all of its State Directors within the range of the black-tailed prairie dog to “ensure that all actions authorized, funded or carried out by their respective field offices do not contribute to the need to list this species” (Colby, Bureau of Land Management, in litt. 1999). The BLM also anticipates implementing a mandatory restriction on prairie dog hunting in portions of south Phillips County, Montana, due to the lack of success of current voluntary closures in the area (October 18, 1999; 64 FR 56213).

We manage over 500 National Wildlife Refuges and their satellites, but only about 15 refuges, satellites, or Waterfowl Production Areas have black-tailed prairie dogs. Only two refuges have any significant amount of occupied habitat. On the Charles M. Russell and UL Bend National Wildlife Refuges in Montana, we manage 5,150 ac (2,090 ha) of black-tailed prairie dog occupied habitat. We have treated burrows with insecticide in an attempt to reduce fleas and disease transmission, and we have moved prairie dogs to recolonize vacant or low-density towns (Matchett 1997). The Rocky Mountain Arsenal National Wildlife Refuge in Colorado is attempting to recover its populations subsequent to repeated plague epizootics (U.S. Fish and Wildlife Service 1998). Shooting of prairie dogs is currently prohibited on all National Wildlife Refuges and satellites. Limited control has occurred on a few wildlife refuges, primarily as a measure to prevent the spread of prairie dogs onto adjacent private lands. At this time, all control efforts regarding the species have been suspended on Service lands (Clark, U.S. Fish and Wildlife Service, in litt. 1999).

The U.S. Forest Service manages approximately 3.7 million ac (1.5 million ha) of National Grasslands, which support approximately 42,460 ac (17,200 ha) of black-tailed prairie dog occupied habitat, approximately 1.1 percent of the National Grasslands (Sidle, U.S. Forest Service, in litt. 1999). In response to a request from the National Wildlife Federation and the positive 90-day finding, the U.S. Forest Service issued a moratorium on control of black-tailed prairie dogs during the current status review period on all lands administered by the U.S. Forest Service. The U.S. Forest Service also noted their intention to manage for larger prairie dog populations via new planning efforts subject to completion and approval (Manning, U.S. Forest Service, in litt. 1999).

The National Park Service is involved with prairie dog control programs through integrated pest management guidelines. During 1982-1992, four National Parks in the northern Great Plains were involved in prairie dog control—Badlands National Park, South Dakota; Wind Cave National Park, South Dakota; Theodore Roosevelt National Park, North Dakota; and Devils Tower National Monument, Wyoming (Roemer and Forrest 1996). In a memorandum dated January 14, 1999, the National Park Service instructed Superintendents of National Parks within the Midwest Region where prairie dogs occur (Badlands, Fort Larned, Scotts Bluff, Theodore Roosevelt, and Wind Cave units) to suspend further treatment of prairie dog colonies (with few exceptions) until a final determination is made on their status (Schenk, National Park Service, in litt. 1999).

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service-Wildlife Services influences prairie dog control programs through its grant-in-aid program to States, which provides technical assistance to other State, Tribal, and Federal agencies, and private landowners, and its distribution of prairie dog toxicants. Roemer (1997) reported that during 1990-1994, the Animal and Plant Health Inspection Service-Wildlife Services was involved in control of prairie dogs over 101,660 ac (41,140 ha). Additionally, they were involved in control programs in the early 1980s at the Pine Ridge Indian Reservation (Oglala Sioux Tribe), South Dakota. The Animal and Plant Health Inspection Service-Wildlife Services has directed and conducted research related to the efficiency of prairie dog and other rodent control.

The Environmental Protection Agency deals indirectly with prairie dog control through pesticide labeling programs including restrictions to protect wildlife. Presently, labeling does not restrict prairie dog control, but does address concerns for the endangered black-footed ferret.

In Canada, the black-tailed prairie dog is designated as vulnerable by the Committee on the Status of Endangered Wildlife in Canada. Control is prohibited, and only private landowners are permitted to shoot prairie dogs (Fargey, Grasslands National Park, pers. comm. 1998).

In Mexico, the black-tailed prairie dog is listed as threatened by the Lista de las Especies Amerzadas, the official threatened and endangered species list of the Mexican Government (SEMARNAP 1994). List et al. (1997) reported that in Mexico, laws exist to stop control, but are often not enforced, and extensive control occurs. There are no protected areas for the black-tailed prairie dog in Mexico (Ceballos et al. 1993).

E. Other Natural or Manmade Factors Affecting the Species' Continued Existence

Control Effort

We believe that control efforts have limited black-tailed prairie dog populations, especially large-scale, well-organized efforts conducted early in the century. These control programs were conducted in response to concerns regarding potential forage competition with domestic livestock. Current control efforts are limited compared to historic efforts, but still impact a significant portion of occupied habitat annually. A well-documented control effort has occurred over most of the range of the black-tailed prairie dog (Anderson et al. 1986, Bell 1921, Cain et al. 1972, Forrest and Proctor in prep., Hanson 1993, Hubbard and Schmitt 1983, Lantz 1903, Lewis and Hassien 1973, Linder et al. 1972, Merriam 1902, Roemer and Forrest 1996, Shriver 1965). Control efforts resulted in extirpation of the black-tailed prairie dog in Arizona (Alexander 1932). Similar control efforts in Texas resulted in the persistence of only remnant populations in areas where, historically, the largest known populations of the species occurred (Bureau of Sport Fisheries and Wildlife 1961, Cheatheam 1977, Cottam and Caroline 1965).

Prairie dog control occurred repeatedly in most areas, and figures cited for acreage controlled may include retreatment of the same areas in subsequent years. Therefore, annual estimates of lands treated do not always equate to total loss of habitat. However, control (usually in conjunction with other factors) has led to the complete loss of occupied habitat in many areas. Organized prairie dog control gained momentum from 1916 to 1920 when prairie dogs were controlled on tens of millions of acres of western rangeland (Bell 1921). Federal programs were responsible for much of this effort (Cain et al. 1972). From 1937 to 1968, 30,447,355 ac (12,331,178 ha) of prairie dog occupied habitat were controlled (Cain et al. 1972). In the 1960s, several States reached their lowest estimates of occupied habitat (Bureau of Sport Fisheries and Wildlife 1961). In 1972, Compound 1080, which was used extensively in prairie dog control efforts, was banned by Presidential Executive Order II 11643. Although prairie dog control continued via other toxicants, it was at a reduced rate.

The most extensive control efforts in recent years have been conducted in the Northern Great Plains (U.S. Forest Service 1998). Roemer and Forrest (1996) summarized recent Federal and State control efforts on approximately 1,045,524 ac (423,437 ha) in South Dakota, Montana, and Wyoming. From 1978 to 1992, an average of 69,701 ac (28,229 ha) were treated annually in these three States. These estimates did not include estimates for private control or control involving indirect State or Federal assistance. Forrest and Proctor (in prep.) estimated that in recent years control conducted at the local level probably affected “tens of thousands” of black-tailed prairie dog occupied habitat on an annual basis. The BIA administered the last large-scale control effort for black-tailed prairie dogs on the Pine Ridge Reservation in South Dakota in the early 1980s. This effort resulted in the eradication of most prairie dogs on approximately 458,618 ac (185,740 ha) from 1980 to 1984. From 1985 to 1986, 240,000 ac (97,000 ha) were retreated (Roemer and Forrest 1996). In 1987, after these efforts, 57,281 ac (23,199 ha) of occupied habitat remained (Tschetter 1988). Current estimates of occupied habitat range from 20,000 to 30,000 ac (8,000 to 12,000 ha) (Yellowhair, Pine Ridge Sioux Tribe, pers. comm. 1999). Following control efforts on Pine Ridge, three additional extensive control efforts targeted for the Cheyenne River and Rosebud Reservations in South Dakota and Fort Belknap Reservation in Montana were halted due to concerns regarding the lack of available black-footed ferret reintroduction sites.

Vulnerability of the Species in Perspective

Three major impacts have had a substantial influence on black-tailed prairie dog populations. The first major impact on the species was the initial conversion of prairie grasslands to cropland in the eastern portion of its range from approximately the 1880s-1920s. The conversion of native prairie to cropland likely reduced black-tailed prairie dog occupied habitat in the United States from about 80 million ac (32 million ha) to about 50 million ac (20 million ha) or less. The second major impact on the species was large-scale control efforts conducted from approximately 1918-1972 in efforts to reduce competition between prairie dogs and domestic livestock. Repeated control efforts likely reduced black-tailed prairie dog occupied habitat in the United States from about 50 million ac (20 million ha) to approximately 364,000 ac (147,000 ha) by 1961 (Bureau of Sport Fisheries and Wildlife 1961). Some limited recovery and subsequent declines have since occurred in these remnant populations. The third major impact on the species was the inadvertent introduction of an exotic disease from the Old World, sylvatic plague, into North American ecosystems in 1908, with the first recorded impacts on the black-tailed prairie dog in the 1940s. These three factors, as well as other additional factors impacting the species, are discussed below.

We believe that many factors, alone, in combination with each other, and synergistically, have influenced and continue to influence black-tailed prairie dog populations. Historically, large black-tailed prairie dog populations successfully coped with various depressant factors, except plague, on a different scale; populations were large and robust, while threats were few with only short-term effects. Presently, most populations are significantly reduced and must cope with many persistent influences that depress populations, both temporally and permanently. Based upon our review of the available information, we conclude that a general long-term, rangewide decline has occurred, in addition to more recent population declines in some areas.

The persistence of the black-tailed prairie dog as a species may appear secure to some observers because it is relatively abundant in absolute numbers when compared with many other species with smaller populations that are not thought to be vulnerable. Many wildlife species in North America that have experienced significant population declines remain viable (e.g., various game species such as the pronghorn (Antilocapra americana)). However, the black-tailed prairie dog is a highly social species that, for the most part, responds to major factors causing population reductions (e.g., plague and control) on the basis of entire colonies rather than on an individual basis. Additionally, adequate regulatory mechanisms are not in place to protect or manage populations of the black-tailed prairie dog, as they are with most game species. Therefore, populations are likely not as viable as their absolute numbers might suggest.

A significant portion of existing black-tailed prairie dog occupied habitat rangewide occurs in a few large complexes. Approximately 36 percent of the remaining occupied habitat for the species in North America occurs in seven complexes, each larger than 10,000 ac (4,000 ha). These complexes include—Buffalo Gap National Grassland/Conata Basin, South Dakota; Cheyenne River Reservation, South Dakota; Fort Belknap Reservation, Montana; Janos Nuevo Casas Grandes, Mexico; Pine Ridge Reservation, South Dakota; Rosebud Reservation, South Dakota; and Thunder Basin National Grassland, Wyoming. These complexes are potentially vulnerable to control efforts or plague.

Extant populations of black-tailed prairie dogs may or may not be large enough to be resilient to ongoing or future environmental challenges and related potential declines. Quammen (1996) provided examples of species that were abundant, but suddenly became very rare. For example, he reported that the passenger pigeon (Ectopistes migratorius) numbered in the billions around 1810 and in the low millions by the 1880s, yet was extinct in the wild by 1900. Habitat destruction and over-harvesting depressed passenger pigeon numbers to a few million, a level too low for a highly social and colonial species to function (Halliday 1980). The black-tailed prairie dog numbered in the billions around 1900, exists as a few million at present, and appears to be declining in a significant portion of its range. The advantages of sociality (e.g., breeding, feeding, predator defense) may no longer offset its modern disadvantages (e.g., vulnerability to an exotic disease and control efforts). Accordingly, the vulnerability of the black-tailed prairie dog to population reductions is likely related less to its absolute numbers than to the number of colonies in which it exists, their size, their geospatial relationship, existing barriers to immigration and emigration, and ultimately the number and nature of the remaining direct threats to the species.

Finding

After a thorough review of the best available scientific and commercial information, we find that sufficient information is currently available to support a determination that listing the black-tailed prairie dog as threatened is warranted. This action is appropriate because of the number and variety of threats that act in concert to adversely affect the species. A significant recent decline in occupied habitat has occurred due to several factors, the most influential of which is the widespread occurrence of plague, an exotic and lethal disease to the species. In concert with plague, the loss of suitable habitat and inadequate regulatory mechanisms have adversely affected remnant fragmented populations. The available information indicates that the species is likely to become endangered throughout all or a significant portion of its range in the foreseeable future.

A major decline in historic black-tailed prairie dog occupied habitat has occurred (perhaps as much as 99 percent). Sixty percent of the species' remnant occupied habitat is vulnerable or very vulnerable to the effects of habitat loss or modification, disease, inadequate regulatory mechanisms, and other factors (Black-footed Ferret Recovery Foundation, in litt. 1999). Based on our review of the available distribution data, we estimate that approximately 30 percent of the historic range no longer supports any appreciable number of black-tailed prairie dogs, and that these reductions occurred at the periphery of the historic range. However, reductions in occupied habitat have also occurred throughout the historic range; approximately 37 percent of the suitable habitat within the historic range in the United States has been fundamentally modified via conversion to cropland and is not available for use by the species (Black-footed Ferret Recovery Foundation, in litt. 1999). Additionally, habitat in approximately 66 percent of the historic range of the species has been degraded by the occurrence of plague (Black-footed Ferret Recovery Foundation, in litt. 1999). These estimates are not additive inasmuch as several factors can affect any given portion of the range.

Recent, widely separated, site-specific declines across the area where 60 percent of the current occupied black-tailed prairie dog habitat now exists appear to be indicative of a general population decline. The overall decline may be similar to the specific decline observed across the State of Montana from 1986 to 1998 when approximately 50 percent of all occupied habitat was lost, largely due to plague (Montana Department of Fish, Wildlife, and Parks 1998). Plague has incrementally extended its range and impacts on black-tailed prairie dogs since it was first documented in the species. It may likely continue to expand into the eastern portions of the species' range in the immediate future, as evidenced by recent reports of predator species' exposure to plague in previously unaffected portions of the black-tailed prairie dog range. A decline of similar magnitude has occurred with populations in Mexico (12 percent of current occupied habitat); however, the decline in Mexico is due to cropland conversion, not plague.

At present, occupied habitat has decreased over the past century by two orders of magnitude (or 99 percent, from approximately 100 million ac to less than 1 million ac). If the magnitude of decline that we have observed due to plague or cropland conversion persists in western portions of the species' range, and manifests itself in eastern portions of the species' range, over the next 30 years existing occupied habitat could decline another order of magnitude to as low as approximately 10 percent of current estimates, or approximately 0.1 percent of historic estimates.

We have evaluated the magnitude and immediacy of threats to the black-tailed prairie dog. The following provides a summary of these evaluations.

Habitat loss and fragmentation are considered a threat of moderate magnitude. The species has lost an estimated 99 percent of its historic occupied habitat, much of it through cropland conversion, largely in the eastern portion of the species' range. However, a considerable amount of potential unoccupied habitat remains, especially in the western portion of the species' range. This unoccupied habitat could be utilized if other factors such as disease and control efforts were not present or were carefully managed via adequate regulatory mechanisms. This threat is considered imminent because habitat loss continues at present in various parts of the species' range from a variety of activities, including cropland conversion, urbanization, change in vegetative communities, and fragmentation.

Overutilization via commercial use of the species as a pet is not considered a threat because of the apparent low number of individuals utilized. Overutilization via recreational shooting is considered a threat of low magnitude. Local populations may be impacted by shooting; however, significant rangewide population declines due to this factor are not likely. This threat is considered imminent because it is ongoing.

Disease is considered a threat of moderate magnitude. Plague has markedly reduced some populations, but has not affected all populations at once. Some population recovery may occur, largely via unaffected adjacent populations, before plague reoccurrence. Plague has impacted the species and its conspecifics throughout a significant portion of their ranges. Black-tailed prairie dog populations demonstrate nearly 100 percent mortality when exposed to plague. An epizootic may affect an entire complex similar to a pathogen affecting an individual animal. The spread of plague in black-tailed prairie dog populations underscores the likelihood that areas as yet unaffected may experience outbreaks in the future. This threat is considered imminent because it is ongoing. Predation is not considered a threat.

Existing regulatory mechanisms are inadequate and considered a threat of moderate magnitude. All States within the current range of the black-tailed prairie dog classify the species as a pest for agricultural purposes and either allow or require its eradication (Mulhern and Knowles 1995). Few regulatory mechanisms exist to aid in conserving the species. This threat is considered imminent because it is ongoing. State wildlife agencies and other interested parties are developing a conservation plan for the species. While we support the States' efforts and will cooperate in conservation actions for the black-tailed prairie dog, at this early stage of development, the conservation assessment and strategy document lacks commitments to specific immediate actions that would affect the status of the species.

Control programs conducted largely in response to concerns related to potential forage competition with domestic livestock are considered a threat of moderate magnitude. Control programs have had significant impacts on population levels in the past. Control efforts resulted in extirpation of the black-tailed prairie dog from Arizona and significant reductions in other States. Current control efforts may impact 10-20 percent of the species' overall population annually (Forrest and Proctor, in prep.). This threat is considered imminent because it is ongoing. Control efforts in some areas could likely be accommodated if adequate regulatory mechanisms were in place that balanced agricultural and wildlife conservation interests.

We conclude that the overall magnitude of threats to the black-tailed prairie dog throughout its range is moderate and the overall immediacy of these threats is imminent. The black-tailed prairie dog is considered a species without subspecies classification. Pursuant to the Service's Listing Priority Guidance (48 FR 43098), a species for which threats are moderate and imminent is assigned a Listing Priority Number of 8. Region 6 currently has nine Candidate species or subspecies that have lower Listing Priority Numbers and, therefore, are in more immediate need of protection. Region 6 also has four species proposed as endangered or threatened, and two species for which proposed rules are under review. Therefore, while we have concluded that the listing of the black-tailed prairie dog as threatened is warranted, an immediate proposal to list is precluded by other, higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants.

References Cited

A complete list of references cited in this notice is available upon request from the South Dakota Field Office (see ADDRESSES section).

Author: The primary author of this document is Pete Gober (see ADDRESSES section).

Authority: The authority for this action is the Endangered Species Act of 1973 as amended (16 U.S.C. 1532 et seq.).