Mountain-Prairie Region
 

12-MONTH ADMINISTRATIVE FINDING, BLACK-TAILED PRAIRIE DOG

Chapter 2 - Table of Contents

2. BACKGROUND INFORMATION

2.1 Taxonomy

2.2 Biology

2.3 Ecology

2.4 Distribution, Abundance, and Trends

2.4.1 Distribution—Rangewide

2.4.2 Abundance—Difficulty and Accuracy of Evaluations

2.4.3 Abundance—Rangewide

2.4.4 Trends—Rangewide

2.4.5 Trends—Regional Differences in Occupied Habitat for the Species

2.4.6 Distribution, Abundance, and Trends—Specific Areas

2.4.6.1 States

2.4.6.2 Canada

2.4.6.3 Mexico


12-MONTH ADMINISTRATIVE FINDING, BLACK-TAILED PRAIRIE DOG

2. BACKGROUND INFORMATION

The Service reviewed numerous scientific publications and reports in the preparation of this 12-month finding. Many of these were available from peer reviewed journals, but some were unpublished reports from various sources. Additionally, the Service acquired information and professional opinions from scientific experts and other parties through personal communication and from comments made in response to the 90-day finding. Although considerable site and issue specific information related to the black-tailed prairie dog was available, most large scale evaluations related to the species were challenged by the extensive range of the species and the numerous factors which have affected it for over a century. Deliberations for this 12-month finding were similarly challenged; however, the Service believes that a reasonable, accurate evaluation of status trends for the species is possible from the best available scientific and commercial information. In particular, the absolute precision of current population estimates (or lack thereof) did not prove as useful as evaluations of various threats and related examinations of the relative magnitude and trends of recent population changes.

2.1 TAXONOMY

There are five species of prairie dogs in North America. They 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 more mesic habitat.

The black-tailed prairie dog was first described by Ord in 1815 from a specimen local to the Upper Missouri River (Hall and Kelson 1959), although the species was first collected by members of the Lewis and Clark expedition of 1804-1806. Pizzimenti (1975) researched the evolutionary divergence of the various taxa and populations of Cynomys using chromosomal studies and serum protein studies of individuals throughout the range of the genus and concluded that the black-tailed prairie dog should be considered a monotypic species. Other authors (Davis 1974, Hall and Kelson 1959, Hollister 1916, Hubbard and Schmitt 1983, Koford 1958, Sager 1996) indicated that there are two subspecies of the black-tailed prairie dog, the Arizona black-tailed prairie dog (C. l. arizonensis) and the major subspecies (C. l. ludovicianus). The lack of an additional descriptive name for the major group has created some confusion; although it is the most numerous and widespread of the two entities, and is usually what is thought of when the species is considered.

The Arizona subspecies (or variety) is 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 is remnant in southwestern New Mexico (Hall and Kelson 1959) and in the Trans-Pecos region of Texas (Davis 1974, Hall and Kelson 1959). Individuals of the variety in Chihuahua, Mexico, comprise the largest remaining prairie dog complex of any prairie dog species or subspecies (Ceballos and Pacheco 1997). Sager (1996) reported the Arizona subspecies as extirpated from southwestern New Mexico where it once occurred, and described the taxonomy of the black-tailed prairie dog in portions of New Mexico as unclear (the major subspecies occurs in the eastern portion of the State). A debate concerning the subspecies classification of the few remaining black-tailed prairie dogs in southwestern New Mexico continues (Hubbard and Schmitt 1983). Accordingly, the Arizona subspecies (or variety), if recognized, is remnant in the United States since none exist in Arizona, and only a few occur west of the Pecos River in southwestern New Mexico and western Texas.

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 in a small area of south-central Canada.

For the remainder of this finding the use of the common name "black-tailed prairie dog" includes both groups discussed above. Based upon the information currently available, the Service concurs with Pizzimenti’s (1975) assessment of the species as monotypic.

2.2 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 approximately 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. Individuals 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). Historically, they generally occurred in large colonies that contained thousands of individuals, covered hundreds of thousands of acres, and extended for miles (Bailey 1905). Most existing colonies are much smaller. When unsuitable habitat such as a hill, tall vegetation, or a stream divides a prairie dog colony, the resulting sub-colonies are called wards (King 1955). Within colonies, prairie dogs live in territorial, harem-polygamous family groups called coteries (Hoogland 1995). Groups of colonies comprise a complex.

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

Black-tailed prairie dogs are not prolific in comparison to many other rodents. Several biological factors determine the reproductive potential of the species. Females usually do not breed until their second year and live 3-4 years (Hoogland 1995, King 1955, Knowles and Knowles 1994). A common misconception in many of the comment letters the Service received was that prairie dogs produce multiple litters in a year. Female black-tailed prairie dogs produce a single litter, usually 4-5 pups, annually (Hoogland 1995, Knowles and Knowles 1994). Therefore, 1 female may produce from 0 to 20 young in its lifetime. In contrast, another female rodent, the meadow mouse (Microtus), can become pregnant at 3 weeks of age, have up to 17 litters in 1 year, and produce as many as 83 young before 1 year of age (Bailey 1924). Conversely, survival of young prairie dogs can be high in some circumstances, especially in low density populations where habitat resources are plentiful and repressive factors such as control or disease are not operative (Garrett et al. 1982); although much lower rates of annual increase or even reductions in colony size can occur where vegetation hinders expansion or constricts existing colonies (Osborn and Allan 1949). For example, on Buffalo Gap National Grassland in South Dakota, during periods of drought and heavy stocking (both conducive to black-tailed prairie dog expansion), annual colony expansion rates approached 25 percent, while ungrazed areas showed expansion rates of 1-2 percent (Schenbeck, U.S. Forest Service, pers. comm. 1999b).

Another misconception in comment letters to the Service is that female black-tailed prairie dogs produce very large litters. Unfortunately, some older scientific literature furthers this perception. For example, Cottam and Caroline (1965) report a colony in Texas that expanded from 3 pairs in 1961 to 2,000 individuals 3 years later. This rate of expansion and survival is not supported by available demographic information (Hoogland 1995, Knowles and Knowles 1994, Miller et al. 1996). A large group of juveniles observed on the top of a single prairie dog mound does not indicate a very large litter, but may reflect communal nursing. Hoogland et al. (1989) found that multi-litter groupings are common among black-tailed prairie dogs because mothers do not discriminate between their own young and the offspring of others. Most pups receive milk from foster mothers. The same author also found that early infanticide resulted in partial or total elimination of 39 percent of all litters born.

Knowles (1985) noted that roads were frequently utilized during dispersal for distances up to 6 miles (10 kilometers). However, 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 reestablishment of individuals in nearby, recently abandoned colonies over the establishment of new colonies. King (1955) observed two types of emigration among black-tailed prairie dogs. The first type occurred when yearling males move in the spring following the appearance of young in the colony. The second type of emigration consisted of older adults leaving a colony in the spring or summer, possibly to avoid excessive attention and interference by the young-of-the-year.

2.3 ECOLOGY

Prairie dogs act in several roles inasmuch as they are prey, provide shelter, modify vegetation, and influence ecological processes in a manner not entirely duplicated by other prairie herbivores (Ceballos and Pacheco 1997, Kotliar et al. 1999, List et al. 1997, Miller et al. 1994, Wuerthner 1997). While the black-tailed prairie dog creates habitat for itself and other species, it also is affected by other species. For example, prairie dogs can create preferential grazing opportunities for herbivores who in turn create opportunities via grazing for the expansion of prairie dog colonies at their perimeters. However, the degree to which the black-tailed prairie dog itself is influenced by these and other prairie species, particularly ungulates, is not well understood. For example, the removal of large numbers of bison (Bison bison) and other native ungulates from the North American prairie may have had effects on the ecology of the black-tailed prairie dog that can no longer be fully evaluated. Similarly, the periodic effects of fire no longer influence much of the remaining fragmented prairie environment.

The Petitioner described the importance of the black-tailed prairie dog to other species; noting that 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 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).

Many authors have recognized the biological importance of the black-tailed prairie dog as a keystone species (Agnew et al. 1986, Ceballos and Pacheco 1997, Clark et al. 1982, Kotliar et al. 1999, Miller et al. 1994, Reading et al. 1989). Keystone species influence ecosystem functions through their activities in unique and significant ways. The ecological effect caused by a keystone species is disproportionate to its numerical abundance and its removal or decline initiates changes in ecosystem structure and a decline in overall species diversity (Kotliar et al.1999, Miller et al. in press, Mills et al. 1993, Paine 1980, Power et al. 1996, Terborgh 1988). However, Stapp (1998) questioned whether the black-tailed prairie dog is truly a keystone species. He recognized various ecological values of the species, but challenged other authors’ view of the overall role of the species. Kotliar et al. (1999) concluded that prairie dogs provide some unique functions compared to other herbivores in the system and that continued decline of the species may lead to a substantial erosion of biological diversity; and, therefore, keystone status is appropriate. The extent to which these interrelationships directly affect the black-tailed prairie dog itself is largely unknown.

2.4 DISTRIBUTION, ABUNDANCE, AND TRENDS

2.4.1 Distribution—Rangewide

The historic range of the black-tailed prairie dog included portions of 11 States, Canada, and Mexico. Today it occurs from extreme south-central Canada to northeastern Mexico and from approximately the 98th 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).

The Petitioner noted that remnant populations of black-tailed prairie dogs are widely distributed within the exterior boundaries of the species’ original range, but that significant range contractions have occurred in Kansas, Oklahoma, Texas, and Arizona. The Service believes that significant range contractions have occurred in Arizona; in western New Mexico and western Texas in the southwestern portion of the species’ historic range; and in Kansas, Nebraska, Oklahoma, South Dakota, and Texas in the eastern portion of the species’ historic range. The Service has determined that these range contractions represent approximately 20 percent of the species’ original range. Only a few individuals, or none at all, remain in these areas.

The BFF Recovery Foundation (1999) estimated that approximately 37 percent of the species’ potential habitat in the United States, has been fundamentally converted to cropland or similar farming practices. This estimate addresses habitat loss that is essentially permanent, but not a range contraction in the usual sense at the periphery of a species’ range. Although the species will occupy abandoned cropland, these lands are generally unavailable for use by the species by virtue of continued disturbance.

Information from State, tribal, and Federal Agencies indicates that approximately 70 percent of all black-tailed prairie dog occupied habitat in the United States is on private or State lands, approximately 20 percent is on tribal lands, and approximately 10 percent is on Federal lands. A disproportionately large percentage of occupied habitat occurs on tribal and Federal lands, based upon the amount of available habitat on tribal and Federal lands as compared with the much larger amount of available habitat on private lands. These percentages are comparable to Knowles’ (1995) conclusions of over 50 percent of occupied habitat occurring on private lands and 30 percent occurring on tribal lands.

Black-tailed prairie dogs are absent from most of the range which they occupied historically, although remnant populations are widely scattered across much of this area. Notably, many land tracts within the historic range have no black-tailed prairie dogs, some have a few black-tailed prairie dogs, and very few have significant numbers of black-tailed prairie dogs.

2.4.2 Abundance—Difficulty and Accuracy of Evaluations

The Service notes the unavailability of any recent, comprehensive, original, single-source, rangewide estimate of occupied habitat for the black-tailed prairie dog and recognizes that such an evaluation would be very difficult to conduct. Several authors have attempted to combine reports of occupied habitat from various sources to provide an overall estimate across the species’ range (Fagerstone and Ramey 1996, Knowles 1995, Knowles 1998, Mulhern and Knowles 1995). However, these efforts have been limited because the range of the species is vast and much of it is remote, and accordingly accurate, comparable information is difficult to obtain. Populations are located irregularly, at varying densities, and may be periodically expanding and/or contracting over time and space due to various combinations of factors. For example, Johnson (South Dakota State University, in litt. 1999) suggested that early estimates vary and some populations at the turn of the century may have increased from pre-European levels. Moreover, census techniques are highly variable. The Service believes that many estimates of black-tailed prairie dog occupied habitat are subject to considerable error. However, precise estimates of occupied habitat may not be necessary to determine general population trends and the vulnerability of the species to various threats. The Service has relied more on some reports than on others based on the methodologies involved and the quality of the information available.

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

Throughout the past century, various parties have attempted estimates of black-tailed prairie dog occupied habitat with varying degrees of precision. Agricultural, pest control, or wildlife managers at the county or regional level have conducted many surveys; however, many of these estimates have not been very accurate. For example, Powell (1992) reported that Kansas conducted questionnaire surveys of prairie dog colonies in Kansas in 1989. Those surveys consisted of questions to USDA Soil Conservation Service (now Natural Resources Conservation Service) personnel and Kansas Conservation Officers about the size and location of prairie dog towns in their counties. A 1990 survey to assess the accuracy of the 1989 survey, using high resolution aerial photography and ground truthing, pointed out the overall lack of value of the questionnaire surveys previously conducted. Results of the questionnaire surveys varied widely, and the accuracy depended on the familiarity of field personnel with their area of jurisdiction.

Another example of the difficulty of obtaining accurate recent estimates of the amount of black-tailed prairie dog occupied habitat is available from Colorado. In a 1990 report the Colorado Department of Agriculture estimated from mail surveys of landowners that Colorado contained approximately 1.5 million acres (600,000 hectares) of prairie dog occupied habitat (Colorado Department of Agriculture 1990). Approximately 973,300 acres (394,200 hectares) of this amount was black-tailed prairie dog occupied habitat. A phone survey to county weed and pest control officials or extension agents in approximately 20 of the 37 counties within the black-tailed prairie dogs’ historic range in Colorado was completed in 1998 (Black-footed Ferret Recovery Foundation in litt. 1998). The intent of the 1998 survey was to revisit the Colorado Department of Agriculture’s estimates from 8 years earlier. In most cases, the 1998 estimates of black-tailed prairie dog occupied habitat were considerably less than those provided by the Colorado Department of Agriculture. Although different methodologies and different sampling times likely affected these results, further comparisons with field studies conducted by Bissell et al. (1979) and a contemporary effort by Patton and Leachman (1991) suggest that reports from Colorado Department of Agriculture (1990) overestimated occupied habitat on a county basis by a factor of as much as 4-10 fold.

The Service has observed that questionnaire efforts generally over-estimate the amount of occupied habitat. For example, the entire amount of occupied habitat in Oklahoma was estimated to be 8,600 acres (3,500 hectares) in a field study by Lomolino (University of Oklahoma, in litt. 1999), while a questionnaire based estimate from one county in Oklahoma for the same year was 50,000 acres (Black-footed Ferret Recovery Foundation in litt. 1998).

Some other types of estimates of occupied habitat are probably more reliable than questionnaire surveys. For example, the State of Montana produced a 1998 Statewide estimate based on field surveys assisted by Global Positioning System technology (Montana Department of Fish, Wildlife, and Parks 1998). Similar efforts have been conducted on some Federal and tribal lands. Studies in Oklahoma have followed black-tailed prairie dog populations for several years (1967, 1972, 1990, 1991, 1992, 1999). Several of these types of efforts in various States have been related to black-footed ferret recovery efforts. Black-footed ferret reintroduction has prompted various black-tailed prairie dog studies and resulted in a good understanding of the location of the remaining, large black-tailed prairie dog complexes (Lockhart, U.S. Fish and Wildlife Service, in litt. 1998). The Forest Service has conducted aerial line transect estimates for the States of Nebraska, North Dakota, South Dakota, and Wyoming, and many National Grasslands Administrative Units, although preliminary estimates are currently available for only North Dakota and South Dakota (Sidle 1999; Sidle, U.S. Forest Service, pers. comm. 1999).

2.4.3 Abundance—Rangewide

The black-tailed prairie dog may be found intermittently in remnant populations throughout much of the range that it once occupied. However, Barko (1997), Fagerstone and Ramey (1996), Knowles (1998), Mulhern and Knowles (1995), and Wuerthner (1997) concluded that there has been an approximate 94-99 percent reduction in the amount of black-tailed prairie dog occupied habitat within this range since about 1900. Generally State wildlife agencies confirm this decline, but some point out that disproportionately more occupied habitat remains in some areas than in others.

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. Merriam (1902) provides one of the earliest accounts of the species’ abundance. He described a colony in Texas of about 25,000 square miles (approximately 16 million acres/6.5 million hectares), with an estimated population of at least 400 million individuals. Bailey (1932) described the Arizona subspecies in the Animas Valley, New Mexico as "an almost continuous prairie-dog town for its whole length and breadth." He estimated that as many as 6.4 million prairie dogs occupied 1,000 square miles (640,000 acres/259,000 hectares) in that region. These accounts provide descriptions of black-tailed prairie dog abundance that may have been representative in the Great Plains at the turn of the last century and no longer occur anywhere in the species’ range. No black-tailed prairie dog populations, or only a few individuals, remain in either the Animas Valley of New Mexico or the area described in Texas.

Seton (1953) estimated that in the late 1800’s there were 5 billion black-tailed prairie dogs over their entire range of 600,000 square miles (384 million acres/155.5 million hectares). Anderson et al. (1986) noted that as a conservative estimate for the early 1900’s, 104 million acres (42 million hectares) of rangeland may have been occupied by all species of prairie dogs. Miller et al. (1996) and Mulhern and Knowles (1995) provide a range for historic occupied habitat by all species of prairie dogs based upon estimates from other authors of 99-247 million acres (40-100 million hectares). Black-tailed prairie dogs had the most extensive range of all the species of prairie dogs; they probably occupied more area than all other species combined (Hoogland 1995).

Historic and recent estimates from several sources of the amount of black-tailed prairie dog occupied habitat for pertinent States, the United States, Mexico, and Canada are summarized in Table 1. The final column contains an acreage figure which the Service believes is a reasonable estimate of current occupied habitat for the species, based upon the best information available. More detailed information for each of the States is presented in Section 2.4.6.1 Distribution, Abundance, and Trends—Specific Areas. It should be noted that the estimates provided by cited authors and others often repeat each others’ estimates. It also is important to remember that many of these historic and recent estimates are variable and subject to error due to their methodologies.

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 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 acres (4,000 hectares). We believe that approximately 768,000 acres (311,000 hectares) of black-tailed prairie dog occupied habitat currently exists rangewide. This estimate is based on the sum of Service estimates from various States in the United States, from Canada, and from Mexico, as discussed under the Statewide Distribution, Trends, and Abundance section below.

Historic abundance also can be estimated by evaluating current land use categories within the historic range of the black-tailed prairie dog. The BFF Recovery Foundation (1999) summarized land use types in the United States using data available from the U.S. Geological Survey. Land use types were grouped into three major categories—grasslands/shrublands, croplands, and other (forest, wetlands, rocky areas, urban areas, etc.). The aerial extent of each category was determined using a Geographic Information System (GIS). Grasslands/shrublands and croplands within the historic range of the species were assumed to have provided suitable potential habitat historically. It has been estimated that approximately 20 percent of all potential habitat was inhabited historically by the species at any given time (Whicker and Detling 1988). Table 2 presents this data. The author noted that these calculations rely on a number of assumptions, but believes they provide a reasonable estimate for historic abundance. This method also has the advantage of presenting a single source comparison of relative abundance between States; whereas other historic estimates for States are variable, since estimates were made both before and after initiation of control efforts, by different individuals, at different points in time, and using different methodologies. It should be noted that the total potential habitat estimate of 393,540,257 acres (159,383,800 hectares) in Table 2 is similar to Seton’s (1953) estimate of 384 million acres (155.5 million hectares) within the range of the species; and the total for 20 percent of potential habitat (occupied habitat) of 78,708,051 acres (32 million hectares) is comparable to Knowles’ (1998) estimate of 111 million acres (45 million hectares) of occupied habitat.

 

2.4.4 Trends—Rangewide

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 throughout North America (Mac et al. 1998). The estimate by the BFF Recovery Foundation (1999) for historic occupied habitat of approximately 79 million acres (32 million hectares) in the United States is less than the estimate by Knowles (1998) of approximately 111 million acres (45 million hectares). However, it is apparent that regardless of which estimate is considered, tens of millions of acres of black-tailed prairie dog occupied habitat once existed in the United States. Moreover, it appears that the amount of occupied habitat has declined from approximately 100 million acres (40.5 million hectares) in the late 1800’s to less than 1 million acres (0.4 million hectares) at present; a decline of approximately two orders of magnitude. A major reduction in historic black-tailed prairie dog occupied habitat has occurred. The species is absent from a significant portion of its historic range despite perceptions to the contrary engendered in part by its conspicuous life history, e.g., its diurnal behavior, its modifications to the landscape, and its persistence in small remnant populations across much of its former range.

In 1961, after this major reduction in black-tailed prairie dog occupied habitat, the Predator and Rodent Control Branch of the Bureau of Sport Fisheries and Wildlife estimated the area occupied by black-tailed prairie dogs in the United States to be approximately 364,000 acres (147,000 hectares) (Bureau of Sport Fisheries and Wildlife 1961). These estimates were based on surveys conducted by district offices in response to concerns regarding declines in prairie dog numbers. The accuracy of these surveys likely varied between districts. The methodology used to arrive at these estimates was not available. However, this report does provide relative estimates of occupied habitat for each species of prairie dog in each State for this time period.

The Arizona Game and Fish Department asserts that (outside the State) the black-tailed prairie dog occurs in all portions of its historic range and that sufficient numbers of individuals remain to recolonize vacant habitat (Shroufe, Arizona Game and Fish Department, in litt. 1998). The AGFD refers to the Predator and Rodental Control Branch report (Bureau of Sport Fisheries and Wildlife 1961) which estimated black-tailed prairie dog occupied habitat across its historic range at 364,056 acres (147,330 hectares) (none in Arizona) and concludes that if this estimate is correct, then the species has increased 46 percent since 1961 to arrive at the current estimates provided in the petition.

Some increases in the amount of black-tailed prairie dog occupied habitat in some areas occurred subsequent to the Executive Order banning the use of the toxicant Compound 1080 in 1972. In 1998, Knowles estimated 677,000 acres (274,000 hectares) of occupied habitat for the species in the United States; however, Knowles also noted that these increases appear to have been limited by the use of toxicants such as zinc phosphide, the continuing spread of sylvatic plague, and other factors (Knowles 1998). Moreover, the majority of this increase (approximately 85 percent) occurred in areas (Montana, South Dakota, and Wyoming) where significant impacts due to disease had not yet occurred (Table 1).

Evaluations of estimates of black-tailed prairie dog occupied habitat in New Mexico have confounded some estimates of rangewide trends for the species. Some survey reports of prairie dogs in New Mexico have combined estimates of occupied habitat for black-tailed and Gunnison’s prairie dogs (both occur in New Mexico). Some confusion developed regarding estimates provided by the Biodiversity Legal Foundation et al. (1998), Mulhern and Knowles (1995), and U.S. Fish and Wildlife (1995). The following discussion addresses this issue. Hubbard and Schmitt (1983) adjusted figures from Bodenchuck (1981) and estimated 497,012 acres (201,220 hectares) of occupied habitat for both species of prairie dogs in New Mexico. Mulhern and Knowles (1995) and U.S. Fish and Wildlife (1995) also reported 497,012 acres (201,220 hectares) of occupied habitat. This acreage figure has been misinterpreted to represent recent (post 1980) acreage of black-tailed prairie dog occupied habitat in the State. This figure also has been included in some United States totals (Mulhern and Knowles 1995), which otherwise refer only to black-tailed prairie dogs. Therefore, the estimate from the National Wildlife Federation (1998) of a potential 30-60 percent reduction in occupied habitat and from Biodiversity Legal Foundation et al. (1998) of a potential 50 percent loss in black-tailed prairie dog occupied habitat during the past 3 years, based on a nationwide decrease from 1.35 million acres (547,000 hectares) (which includes both species for New Mexico) in 1995 (Mulhern and Knowles 1995) to less than 700,000 acres (280,000 hectares) (which includes only black-tailed prairie dogs for New Mexico) in 1998 (Knowles 1998), is incorrect. The Biodiversity Legal Foundation subsequently revised its estimate to acknowledge this inconsistency (Biodiversity Legal Foundation et al. in litt. 1998).

Survey efforts in some areas have noted significant declines in the amount of black-tailed prairie dog occupied habitat over the last few decades. The Forest Service has mapped all black-tailed prairie dog colonies within the Northern Great Plains National Grasslands and Forests. These 10 grasslands, covering approximately 3.7 million acres (1.5 million hectares), included a maximum of 86,220 acres (34,890 hectares) of black-tailed prairie dog occupied habitat, according to data collected from the 1970’s to 1990’s. In 1997, the Forest Service mapped 39,420 acres (15,965 hectares) of occupied habitat in the same areas, indicating a 54 percent decline (U.S. Forest Service 1998). Data provided by the Forest Service in 1999 (Sidle, U.S. Forest Service, in litt. 1999) confirmed losses in occupied habitat for the National Grasslands with a total decline of 58 percent from the 1970’s to the present. Much of the recent decline noted by the Forest Service was due to prairie dog control programs. A few site specific areas where occupied habitat has recently increased on National Grasslands do not significantly affect this trend.

Lockhart (U.S. Fish and Wildlife Service, in litt. 1998) reported that the recovery program for the black-footed ferret has identified on an ongoing basis since the 1980’s those 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 acres (4,000 hectares) of prairie dog occupied habitat. In the late 1980's, the Black-footed Ferret Interstate Coordinating Committee identified dozens of potential sites that may have qualified as suitable for ferret. However, by 1994 only 16 sites were identified and by 1998 this number was reduced to 10 sites (7 being black-tailed prairie dog sites).

Part of this decline in the number of known large prairie dog complexes was the extreme reduction in the amount of occupied habitat and individuals within a number of formerly large black-tailed prairie dog complexes, i.e., Fort Belknap Reservation and southern Phillips County in north central Montana, the Northern Cheyenne Reservation in southeastern Montana, the Recluse site in northeastern Wyoming, Rocky Mountain Arsenal National Wildlife Refuge in central Colorado, Comanche National Grasslands in southeastern Colorado, and Cimarron County in the Oklahoma panhandle. Black-tailed prairie dog populations at these sites appear to have been reduced by as much as 90 percent within the last 10-15 years, largely in the western portion of the species’ range, due to sylvatic plague, although limited recovery has been observed at some locales. These reductions in large complexes due to disease occurred across approximately a 1,000-mile (1,600-kilometer) reach of the species’ range, which includes approximately 50 percent of its total range. This region has several similarities in habitat and range land characteristics as well as similar threats, in particular the presence of sylvatic plague (see Section 3.3.1). Populations in New Mexico and Texas also were reported to have been affected by sylvatic plague during this period.

In summary, significant recent population declines in many large black-tailed prairie dog complexes have occurred in the last few decades. 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 have increased marginally or remained generally constant during the same period (see Section 2.4.5.1 for discussions of individual States). A large scale perspective of these various trends is presented in Section 3.6.

2.4.5 Trends—Regional Differences in Occupied Habitat for the Species

Data from Knowles (1998) indicates that Arizona, New Mexico, Oklahoma, and Texas may have contained more than 50 percent of the historic black-tailed prairie dog occupied habitat in the United States, but currently account for less than 10 percent of the remaining occupied habitat. A similar comparison between more conservative historic estimates of occupied habitat in Table 2 and the Services’ current estimates in Table 1 indicate similar trends (e.g., 40 percent of historic occupied habitat, 18 percent of current occupied habitat). The existence of large amounts of Federal and tribal lands in the more northerly portion of the species’ range may account in part for the current larger regional prairie dog populations in these areas; land ownership in the southern range is disproportionately more private and may be more intensively managed in ways that do not support prairie dogs. Also, a longer history of disease (i.e., sylvatic plague) in the southwestern States may account in part for smaller regional black-tailed prairie dog populations. Conversely, South Dakota in the northern portion of the species’ range has relatively large amounts of prairie grasslands in Federal and tribal ownership, is the only State where sylvatic plague is not known to have affected black-tailed prairie dog populations, has most of the remaining large black-tailed prairie dog complexes (four out of seven), and still has disproportionately more of its historic black-tailed prairie dog population than other States.

Approximately 66 percent, or 300 million acres (122 million hectares) of the black-tailed prairie dog range in the United States estimated in Table 2 is affected by sylvatic plague (Black-footed Ferret Recovery Foundation in litt. 1999). This area includes the western portions of the species’ range. Additionally, another important factor which 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 the more intensive agricultural use in the eastern portion of the species’ range. The BFF Recovery Foundation (1999) used GIS to determine the amount of habitat (grass/shrub lands) currently available to the species. In the plague-free portion of the species’ range (34 percent), less than 33 percent of the land is available to the species as non-cropland. Therefore, only approximately 10 percent of the black-tailed prairie dog range is both plague-free and currently suitable (i.e., not tilled) for the species. The majority of plague-free, suitable range occurs in South Dakota.

2.4.6 Distribution, Abundance, and Trends—Specific Areas

Eleven States and three Tribes provided comments regarding distribution, abundance and trends of the black-tailed prairie dog to the Service. These responses and other information regarding the historical and recent occurrence of the species are described below for each State, Tribe, and Country. This information also is presented in Table 1 where estimates from all available sources are summarized. Several eestimates of black-tailed prairie dog occupied habitat were available for each State. The dates, methodologies, and ultimately the reliability of these estimates varied. Generally, the Service 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 Service estimates to the nearest 1,000 acres.

2.4.6.1 States.

Arizona

Distribution--Black-tailed prairie dog occupied habitat existed in southeastern Arizona prior to rodent control efforts (Hall and Kelson 1959). Specific reports by county vary as to the occurrence of the species. Information provided by Van Pelt (Arizona Game and Fish Department, in litt. 1998) noted the species in Cochise and Graham Counties. Information from Fagerstone and Ramey (1996) as delineated by the Black-footed Ferret Recovery Foundation (in litt. 1999) noted the species in Cochise and Santa Cruz Counties as well as portions of Pima, Graham, Pinal, and Greenlee Counties. The black-tailed prairie dog is extirpated at present in the State.

Abundance--Approximately 2 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Arizona historically (Table 2), although a smaller estimate of 650,000 acres (263,000 hectares) also has been reported (Knowles 1998; Van Pelt, Arizona Game and Fish Department, in litt. 1998). This species largely disappeared in the State as early as 1932 (Alexander 1932), although a few small colonies may have persisted until as recently as 1959-1960 (Cockrum 1960). The species is extirpated at present in Arizona.

Trends--Approximately 5 percent of the potential black-tailed prairie dog habitat in Arizona has been converted to cropland (Table 2). The Arizona Game and Fish Department believes that potential prairie dog habitat still exists in Arizona, but notes that this habitat type is "declining at an alarming rate." It also notes that "unquestionably, the black-tailed prairie dog has suffered well-documented, range-wide population declines that include extirpation from Arizona. In some parts of the currently occupied range, the surviving local (and typically fragmented) populations also face continued threats." The AGFD identified mesquite woodland invasion of grassland habitats as part of the reason for grassland habitat decline (see Section 3.1.3). It hypothesized that the reduction in grassland habitats "could be due to the accumulated effects of fire suppression, grazing practices and perhaps, the elimination of the black-tailed prairie dog" (Shroufe, Arizona Game and Fish Department, in litt. 1998).

Service Evaluation--The Service believes that intensive grazing in about 1900 may have encouraged the expansion of black-tailed prairie dog occupied habitat in Arizona, and that control efforts 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, disease is an additional factor that could affect the future viability of previously occupied habitat for the black-tailed prairie dog in the State. Arizona is near the identified epicenter for outbreaks for this disease (Gage, Center for Disease Control, pers. comm. 1998). However, in Arizona, sylvatic plague may not occur at elevations below 4,500 feet (1,372 meters), where most of the species occurred historically (Shroufe, Arizona Game and Fish Department, in litt. 1999).

The Service does not agree with AGFD’s comment that recolonization of formerly occupied habitat by the black-tailed prairie dog is assured across the species’ range due to its perceived wide distribution and abundance. The extirpation of most historic populations (and burrow systems), vegetative community changes (e.g., brush invasion of grasslands), landscape changes (e.g., cropland conversion, urbanization), and the establishment of sylvatic plague in North America may limit any extensive reoccupation of its former range by the species. Additionally, most historic black-tailed prairie dog occupied habitat no longer exists and source populations for recolonization are often isolated.

Colorado

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout the eastern half of Colorado, 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. The Colorado Division of Wildlife believes that the species is widely distributed across short-grass prairie habitats in the eastern third of the State, quite common in the urban front-range area west of Interstate 25, and is expanding in some locales (Kahn, Colorado Division of Wildlife, in litt. 1998).

The Service estimates that approximately 96 percent of black-tailed prairie dog occupied habitat in Colorado occurs on private and State lands and 4 percent occurs on Federal lands.

Abundance--Approximately 7 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Colorado historically (Table 2). Approximately 14 percent of occupied habitat in the United States currently exists in Colorado (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Colorado range from 7 million acres (2.8 million hectares) historically to 44,000 acres (18,000 hectares) in 1998 (Knowles 1998). This reduction in occupied habitat is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

Another historic estimate of black-tailed prairie dog occupied habitat in Colorado is 3 million acres (1.2 million hectares) in 1903 (Clark 1989). In 1961, the Predator and Rodent Control Branch report estimated 96,000 acres (39,000 hectares) of occupied habitat (Bureau of Sport Fisheries and Wildlife 1961). In 1979, it is estimated that there were 89,000 acres (36,000 hectares) of occupied habitat in the State (Van Pelt in prep.). A 1990 survey by the Colorado Department of Agriculture estimated 1.5 million acres (600,000 hectares) of prairie dog occupied habitat in Colorado (Colorado Department of Agriculture 1990). Approximately 973,000 acres (394,000 hectares) of this amount was black-tailed prairie dog habitat. A 1998 telephone survey canvassing Colorado agricultural extension or weed and pest agents (Black-footed Ferret Recovery Foundation in litt. 1998) estimated 326,000 acres (132,000 hectares) of black-tailed prairie dog occupied habitat. This survey noted marked differences in occupied habitat for the species in nearly all counties surveyed when compared to the CDA estimate. Other recent estimates of occupied habitat for the species report less than 100,000 acres (40,500 hectares) (Knowles 1995) and, most recently, 44,000 acres (18,000 hectares) (Knowles 1998). Knowles (1998) noted that his estimate was speculative and based on available mapping information.

Recent estimates of existing black-tailed prairie dog occupied habitat at specific locations include—1,320 acres (535 hectares) at Rocky Mountain Arsenal National Wildlife Refuge near Denver (Seery, U.S. Fish and Wildlife Service, pers. comm. 1999), 1,374 acres (556 hectares) at Comanche National Grasslands (0.31 percent of Federal lands within Comanche National Grasslands), and 731 acres (296 hectares) at Pawnee National Grasslands (0.38 percent of Federal lands within Pawnee National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999).

The Service estimates that 93,000 acres (43,000 hectares) of black-tailed prairie dog occupied habitat occur in the State. This figure is based upon the sum of estimates for the Denver Metropolitan Area and for remaining potential black-tailed prairie dog habitat in the State. For the Denver Metropolitan Area, data provided by Skiba (Colorado Division of Wildlife, pers. comm. 1999) and modified by Seery (U.S. Fish and Wildlife Service, pers. comm. 1998) (see Trends below) were utilized. For the remaining potential habitat in the State, data provided by the BFF Recovery Foundation (in litt. 1999) regarding potential black-tailed prairie dog habitat in Colorado and a 0.5 percent occupancy rate based upon recent Forest Service data for the Pawnee National Grasslands Administrative Unit were utilized. An occupancy rate for the Pawnee National Grasslands Administrative Unit (3,951 acres/1,600 hectares of occupied habitat in the 755,200 acres/305,860 hectares administrative unit) was selected because it was the only non-urban area that contained both Federal and private holdings. This estimate is similar to estimates provided by Knowles (1995) and Van Pelt (in prep.) for Colorado.

Trends--Approximately 43 percent of the potential black-tailed prairie dog habitat in Colorado has been converted to cropland (Table 2). The CDOW shares the National Wildlife Federation’s concern regarding the long term degradation of prairie ecosystems, specifically the loss of large (greater than 5,000-acre/2,000-hectare) colonies, but believes that large complexes are unlikely to occur in the State in the future (Kahn, Colorado Division of Wildlife, in litt.1998).

Recent declines have occurred on the Comanche National Grasslands in Colorado, where approximately 90 percent of the black-tailed prairie dog occupied habitat was lost between 1995 and 1998. These declines, from 4,500 acres (1,820 hectares) in 1994-1995 to 500 acres (200 hectares) in 1998, were likely due to sylvatic plague (Cully 1998). Recent surveys indicate recovery to 1,374 acres (556 hectares) of occupied habitat on the Comanche National Grasslands (Sidle, U.S. Forest Service, in litt. 1999). Long-term declines have been noted at the Rocky Mountain Arsenal National Wildlife Refuge due to recurring sylvatic plague outbreaks (U.S. Fish and Wildlife Service 1998) despite periodic limited recovery. Occupied habitat declined from approximately 4,500 acres (1,823 hectares) in 1988 to 1,320 acres (535 hectares) in 1999 with periodic increases and declines related to recurring plague events (Seery, U.S. Fish and Wildlife Service, pers. comm. 1999). In 1994, CDOW mapped 42,500 acres (17,200 hectares) of occupied habitat in the Denver Metropolitan Area (Skiba, Colorado Division of Wildlife, pers. comm. 1999); however, since then there has been approximately a 50 percent decline due largely to sylvatic plague and also urbanization (Seery, U.S. Fish and Wildlife Service, pers. comm. 1998) (Figure 1).

Service Evaluation--The Service believes that black-tailed prairie dog occupied habitat in Colorado has significantly declined from historic levels. There is a large disparity in recent Statewide estimates of remnant occupied habitat. However, the Service believes that trends at specific locations within the State (50 percent decline in Denver Metropolitan Area from 1994 to 1998, 70 percent decline at Rocky Mountain Arsenal National Wildlife Refuge from 1988 to 1999, and a 90 percent decline at Comanche National Grasslands from 1995 to 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.

Kansas

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout the western two-thirds of Kansas, west of approximately the 97th meridian (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) in recent years (Vanderhoof and Robel 1992). The greatest amount of occupied habitat exists in the western third of the State (Vanderhoof et al. 1994).

The Service estimates that approximately 97 percent of black-tailed prairie dog occupied habitat in Kansas occurs on private and State lands and 3 percent occurs on Federal lands.

Abundance--Approximately 10 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Kansas historically (Table 2). Approximately 6 percent of occupied habitat in the United States currently exists in Kansas (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Kansas range from 2.5 million acres (1 million hectares) historically to 36,000 acres (15,000 hectares) in 1998 (Knowles 1998). This reduction in occupied habitat is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1957, black-tailed prairie dog occupied habitat in the State was estimated at 57,000 acres (23,000 hectares) (Smith 1958). The Bureau of Sport Fisheries and Wildlife (1961) estimated that the species occupied 50,000 acres (20,000 hectares) of habitat. In 1972, the species was reported to occupy approximately 36,000 acres (15,000 hectares) of habitat in the State (Henderson and Little 1973). A 1992 survey of western counties in Kansas (Vanderhoof and Robel 1992) estimated 47,000 acres (19,000 hectares) of black-tailed prairie dog occupied habitat. The BFF Recovery Foundation phone survey estimated that 147,000 acres (60,000 hectares) of species occupied habitat were present in Kansas (Black-footed Ferret Recovery Foundation in litt. 1998). Knowles (1998) estimated that there were approximately 36,000 acres (15,000 hectares) of occupied habitat in the State.

The only available recent estimate for black-tailed prairie dog occupied habitat at a specific location is 1,287 acres (521 hectares) on the Cimarron National Grassland (1.19 percent of Federal lands within Cimarron National Grassland) in the southwest corner of the State (Sidle, U.S. Forest Service, in litt. 1999).

The Service estimates 42,000 acres (17,000 hectares) of black-tailed prairie dog occupied habitat exist Statewide. This figure represents the mid-point between estimates of Vanderhoof and Robel (1992) and Knowles (1998) for Kansas and acknowledges recent declines reported by Powell (1992) and Sidle (U.S. Forest Service, pers. comm. 1998).

Trends--Approximately 74 percent of the potential black-tailed prairie dog habitat in Kansas has been converted to cropland (Table 2). The Kansas Department of Wildlife and Parks notes that the amount of black-tailed prairie dog occupied habitat has been greatly reduced from historic accounts. However, it believes that the remnant population has been relatively stable for the last 10-15 years (Williams, Kansas Department of Wildlife and Parks, in litt. 1998). This stability may be due, in part, to the fact that sylvatic plague in black-tailed prairie dogs does not appear to be widespread in the State; although Cully (U.S. Geological Survey, Biological Resources Division, pers. comm. 1998) has verified a sylvatic plague epizootic in black-tailed prairie dogs in Kansas on the Cimarron National Grasslands, where colonies infected in 1996 became inactive by late 1997. He believes that this sylvatic plague epizootic still affects prairie dog populations in this area.

Powell (1992), using high resolution aerial photographs, compared black-tailed prairie dog town numbers and total black-tailed prairie dog occupied habitat for three Kansas Counties in 1990 with a 1986 survey done by Lee and Henderson (1989) which used similar methodology. A comparison of Meade, Gray, and Hamilton Counties indicated that a 50 percent average reduction in the number of colonies and a 17 percent average reduction in occupied habitat occurred from 1986 to 1990.

The Forest Service documented recent declines of 25 percent in black-tailed prairie dog occupied habitat from 1988 to 1998 on the Cimarron National Grasslands in Kansas (Sidle, U.S. Forest Service, pers. comm. 1998). This decline has been related to the recent verification of sylvatic plague in the State (Cully, U.S. Geological Survey, Biological Resources Division, pers. comm. 1998).

Service Evaluation--The Service believes that black-tailed prairie dog occupied habitat in Kansas has declined significantly from historic estimates, but has likely been stable to slightly declining in recent years (Figure 2). 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.

Montana

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat in the eastern two-thirds of Montana, east of the 110th meridian (Flath and Clark 1986), with the exception of the northeastern corner of the State (Hall and Kelson 1959). Known concentrations currently exist in southern Phillips County, Fort Belknap Reservation, Custer County, Charles M. Russell National Wildlife Refuge, and the Crow Reservation.

The Service estimates that approximately 43 percent of black-tailed prairie dog occupied habitat in Montana occurs on private and State lands, 29 percent on Federal lands, and 28 percent occurs on tribal lands (Montana Department of Fish, Wildlife, and Parks in prep.).

Abundance--Approximately 14 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Montana historically (Table 2). Approximately 10 percent of occupied habitat in the United States currently exists in Montana (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Montana range from 6 million acres (2.4 million hectares) historically (Knowles 1998) to 28,286 acres (11,456 hectares) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The most recent estimate of occupied habitat is 66,420 acres (26,900 hectares) (Montana Department of Fish, Wildlife and Parks 1998). This reduction in habitat from historic estimates to the present is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

The Montana Department of Fish, Wildlife and Parks believes that the historic information regarding size and extent of prairie dog colonies in Montana (and elsewhere) is anecdotal or the product of extrapolations from archived descriptions and disputes this estimate of loss (Graham, Montana Department of Fish, Wildlife, and Parks, in litt. 1998). Flath and Clark (1986) estimated that black-tailed prairie dogs historically occupied a minimum of 1.47 million acres (596,000 hectares) in the eastern two-thirds of Montana. This estimate was based on railroad surveys conducted from 1908 to 1914 throughout nearly one-half of the species’ range in Montana. The authors estimated that a greater than 90 percent reduction in occupied habitat occurred between 1914 and 1986. Flath and Clark (1986) also reported 125,000 acres (51,000 hectares) of black-tailed prairie dog occupied habitat Statewide in 1986. Campbell (1989) estimated more than 100,000 acres (40,500 hectares) of occupied habitat Statewide. MDFWP (1998) reported approximately 66,420 acres (26,900 hectares) of black-tailed prairie dog occupied habitat in the State based upon an effort which included—revisiting sites previously recorded by Campbell (1989), additional field surveys, agency interviews, and collecting survey information from BIA and Bureau of Land Management (BLM). Knowles (1998) also reported a similar estimate of 65,000 acres (26,000 hectares) in the State from the same data set. The MDFWP believes that the techniques used to obtain this information resulted in an accurate minimum estimate for the State (Graham, Montana Department of Fish, Wildlife, and Parks, in litt. 1998).

Comments received from one individual disagreed with the findings of MDFWP (1998) regarding occupied habitat in the State (Moore, pers. comm. 1999). Moore concluded, based on ancillary information gathered during big game aerial surveys he had conducted for MDFWP in portions of two counties in the State, that black-tailed prairie dog occupied habitat could be as much as four times that estimated by MDFWP. However, comparisons of ground based GIS data sets with this information indicate that Moore’s estimates were approximately 50 percent higher than actual acreage amounts (Black-footed Ferret Recovery Foundation, pers. comm. 1999; Matchett, U.S. Fish and Wildlife Service, pers. comm. 1999). Moore also reported more colonies than identified by MDFWP, but the Service was unable to evaluate this information due to data limitations and time constraints. Moore did not discuss if an effort was made during aerial surveys to differentiate between active and inactive colonies. Additionally, comments provided by Moore indicated that some of the colonies noted as black-tailed prairie dog occupied habitat may have been occupied only by ground squirrels. The Service believes that Moore’s inference of potentially 266,000 acres (108,000 hectares) of black-tailed prairie dog occupied habitat in Montana (based on extrapolating the Montana estimate 4) is likely inflated given the relatively thorough effort expended by Flath and Clark (1986), Clark (1989), and MDFWP (1998), as well as the trend information (see below) for all available discrete, relatively large sites in Montana where black-tailed prairie dog occupied habitat declined similarly from 1986 to 1998.

Recent estimates of existing black-tailed prairie dog occupied habitat at specific locations include 14,230 acres (5,763 hectares) at Fort Belknap Reservation (Kaiser, Bureau of Indian Affairs, pers. comm. 1999); 11,042 acres (4,472 hectares) in Phillips County; 5,961 acres (2,414 hectares) in Custer County; 5,147 acres (2,085 hectares) at the Charles M. Russell National Wildlife Refuge; and 3,911 acres (1,584 hectares) at the Crow Reservation (Montana Department of Fish, Wildlife, and Parks 1998). More recent preliminary surveys on the Crow Reservation indicate that approximately 10,000 acres (4,050 hectares) of occupied habitat may exist here (Graham, Montana Department of Fish, Wildlife, and Parks, in litt. 1999).

The Service believes that 65,000 acres (26,000 hectares) of black-tailed prairie dog occupied habitat is a reasonable Statewide estimate.

Trends--Approximately 30 percent of the potential black-tailed prairie dog habitat in Montana has been converted to cropland (Table 2). Following a major reduction in occupied habitat from approximately 1900 to 1961, black-tailed prairie dog populations in the State apparently increased between 1961 and 1986 and then experienced significant declines due to sylvatic plague. MDFWP (1998) noted that black-tailed prairie dog occupied habitat declined by approximately 50 percent from the estimates of the late 1980’s, largely due to sylvatic plague. In southern Phillips County occupied habitat declined from 26,123 acres (10,580 hectares) in 1988 to 13,372 acres (5,416 hectares) in 1998, following plague epizootics (Matchett, U.S. Fish and Wildlife Service, pers. comm. 1999). Occupied habitat on Fort Belknap Reservation declined from approximately 24,000 acres (9,700 hectares) in 1990 to approximately 11,000 acres (4,500 hectares) in 1996 and recovered slightly to 13,475 acres (5,457 hectares) in 1998. A subsequent sylvatic plague outbreak was reported in September, 1999 (Hanebury, U.S. Fish and Wildlife Service, pers. comm. 1999). Occupied habitat on the Northern Cheyenne Reservation declined from 10,758 acres (4,357 hectares) in 1992 to approximately 650 acres (263 hectares) in 1994 and recovered slightly to 980 acres (400 hectares) in 1998 (Montana Department of Fish, Wildlife, and Parks 1998, Montana Department of Fish, Wildlife, and Parks in prep.) (Figure 1).

MDFWP states that "in the absence of active management actions, prairie dogs could disappear from marginal habitats at the western extent of their range in Montana. However, this would not threaten the species with extinction so long as the primary prairie dog complexes in Montana are maintained" (Graham, Montana Department of Fish, Wildlife, and Parks, in litt. 1998).

Service Evaluation--The Service believes that there have been significant declines from historic estimates of black-tailed prairie dog occupied habitat in Montana. Current accurate minimum estimates for black-tailed prairie dog occupied habitat are available. Recently, black-tailed prairie dog complexes in Montana have been significantly impacted by sylvatic plague and may continue to decline, although some site-specific increases have occurred. However, Young (University of Arizona, pers. comm. 1998) believes that black-tailed prairie dog populations at Northern Cheyenne Reservation will not recover to pre-plague levels. Matchett (U.S. Fish and Wildlife Service, pers. comm. 1999) stated that he was unaware of any relatively large black-tailed prairie dog complex in the northern Great Plains that had recovered to its former population levels after initial and subsequent plague epizootics.

Nebraska

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout most of Nebraska west of the 97th meridian (Hall and Kelson 1959, Knowles 1995). The Sandhills in the north-central portion of the State include approximately 15 million acres (6 million hectares) which provide only limited suitable habitat (Black-footed Ferret Recovery Foundation in litt. 1999). Presently, the species appears to be scattered throughout the same area, but at much reduced numbers, especially east of the 99th meridian. Populations are known to occur in the western panhandle, southwest of the Platte River, and in central Nebraska.

The Service estimates that approximately 98 percent of black-tailed prairie dog occupied habitat in Nebraska occurs on private and State lands and 2 percent occurs on Federal lands.

Abundance--Approximately 11 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Nebraska historically (Table 2). Approximately 9 percent of occupied habitat in the United States currently exists in Nebraska (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Nebraska range from 6 million acres (2.4 million hectares) historically (Knowles 1998) to 30,000 acres (12,000 hectares) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The most recent estimate of occupied habitat is 60,000 acres (24,000 hectares) (Knowles 1998). This reduction in occupied habitat from historic times to the present is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1971, an estimated 15,000 acres (6,000 hectares) of black-tailed prairie dog occupied habitat remained in the State (Lock 1973). The BFF Recovery Foundation phone survey estimated 80,000 acres (32,000 hectares) of black-tailed prairie dog occupied habitat in the State (Black-footed Ferret Recovery Foundation in litt. 1998). Other current estimates indicate approximately 60,000 acres (24,000 hectares) of occupied habitat in Nebraska (Knowles 1998). The Nebraska Game and Parks Commission estimates 60,000-80,000 acres (24,000-32,000 hectares) of occupied habitat exist in the State (Amack, Nebraska Game and Parks Commission, in litt. 1998). It believes that these population levels are stable. An additional estimate of occupied habitat in 1999 is anticipated from aerial surveys recently conducted by the Forest Service (Sidle, U.S. Forest Service, pers. comm. 1999).

The only estimates of black-tailed prairie dog occupied habitat at specific locations are 741 acres (300 hectares) at Oglala National Grasslands (0.78 percent of Federal lands within Oglala National Grasslands) and 69 acres (28 hectares) at Bessey National Grasslands (0.07 percent of Federal lands within Bessey National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999).

The Service believes that 60,000 acres (24,000 hectares) of black-tailed prairie dog occupied habitat is a reasonable Statewide estimate for Nebraska.

Trends--Approximately 57 percent of the potential black-tailed prairie dog habitat in Nebraska has been converted to cropland (Table 2). Following significant historic declines in occupied habitat and some limited recovery, the amount of occupied habitat in recent years appears fairly stable (Figure 2).

Service Evaluation--The Service believes black-tailed prairie dog occupied habitat in Nebraska has been significantly reduced from historic estimates and likely has been stable to slightly declining in recent years (Figure 2). This stability may be due, in part, 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 panhandle where it has impacted some black-tailed prairie dog populations (Virchow et al. 1992).

New Mexico

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout the southern and eastern two-thirds of the State (Bailey 1932, Hall and Kelson 1959). Hubbard and Schmitt (1983) estimated that the overall range of the species had been reduced by one-fourth in New Mexico by 1983, particularly in the southern portion of the State. Large complexes documented historically, as in Animas Valley in 1908 (Bailey 1932), no longer exist, although a limited, experimental reintroduction effort has been undertaken there (Spangle, U.S. Fish and Wildlife Service, pers. comm. 1999). Presently, the species appears to exist in remnant populations in scattered locations, generally east of the Pecos River (Findley et al. 1975). Recent studies by Sager (1996) and Paternoster (1997) report that the black-tailed prairie dog is limited in its occurrence in New Mexico. The New Mexico Department of Game and Fish believes that in these areas of the State where inventories have been conducted black-tailed prairie dogs "occupy only small areas, consist of small populations and represent isolated colonies" (Maracchini, New Mexico Department of Game and Fish, in litt. 1998).

The Service estimates that approximately 98 percent of black-tailed prairie dog occupied habitat in New Mexico occurs on private and State lands and 2 percent occurs on Federal lands.

Abundance--Approximately 11 percent of black-tailed prairie dog occupied habitat in the United States may have existed in New Mexico historically (Table 2). Approximately 6 percent of occupied habitat in the United States currently exists in New Mexico (Table 1). Statewide estimates of occupied habitat noted in Table 1 for New Mexico range from over 6.64 million acres (2.69 million hectares) historically (Bailey 1932) to 15,000 acres (6,000 hectares) in 1998 (Knowles 1998). This reduction in occupied habitat is greater than 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

The Bureau of Sport Fisheries and Wildlife (1961) estimated that 17,330 acres (7,000 hectares) of black-tailed prairie dog occupied habitat existed in New Mexico in 1961. Bodenchuck (1981) conducted limited surveys in New Mexico which reported approximately 42,000 acres (17,000 hectares) of black-tailed prairie dog occupied habitat. He also estimated that the black-tailed species represented 27.5 percent of the reported total for all species of prairie dogs in the State. He projected (based upon the percentage of responses returned) total occupied habitat for all prairie dog species in the State to be 497,000 acres (201,000 hectares). If the percentage of 27.5 percent black-tailed prairie dogs also is projected, total black-tailed prairie dog occupied habitat for the State was approximately 137,000 acres (55,000 hectares) in 1981. The Service recognizes that nonrespondent follow-up surveys were not conducted and that this projection may be inflated due to bias. In 1998, the BFF Recovery Foundation phone survey estimated 112,000 acres (45,000 hectares) of black-tailed prairie dog occupied habitat in the State (Black-footed Ferret Recovery Foundation in litt. 1998). However, the BFF Recovery Foundation included seven counties in their survey which Bodenchuck (1981) classified as within the range of the Gunnison’s prairie dog. If acreage estimates for these counties are deleted, approximately 107,000 acres (43,000 hectares) of black-tailed prairie dog occupied habitat would be its revised estimate for New Mexico.

Some survey reports of prairie dogs in New Mexico have combined black-tailed and Gunnison’s prairie dogs (both occur in New Mexico). The lumping of these species has confounded evaluation of various reports. Some confusion exists regarding estimates provided by the Biodiversity Legal Foundation et al. (1998), Mulhern and Knowles (1995), and U.S. Fish and Wildlife (1995). Hubbard and Schmitt (1983) adjusted figures from Bodenchuck (1981) and estimated 497,012 acres (201,220 hectares) of occupied habitat for both species of prairie dogs in New Mexico. Mulhern and Knowles (1995) and U.S. Fish and Wildlife (1995) also reported 497,012 acres (201,220 hectares) of occupied habitat. This acreage figure includes occupied habitat for both Gunnison’s and black-tailed prairie dog.

Recent estimates of existing black-tailed prairie dog occupied habitat at specific locations include 613 acres (248 hectares) at Kiowa National Grasslands (0.45 percent of Federal lands within Kiowa National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999), 1,870 acres (757 hectares) in Roosevelt County and 1,304 acres (528 hectares) in Curry County (Paternoster 1997).

Sager (1996) surveyed 4 northeastern counties and found 1,191 individual black-tailed prairie dogs at 64 sites. Paternoster (1997) surveyed 2 counties in east central New Mexico and counted 77 black-tailed prairie dog colonies totaling 3,174 acres (1,285 hectares). Many colonies were small in size and had a very low density of animals. Sager (1996) and Paternoster (1997) do not provide any Statewide estimates of occupied habitat; however, they do provide detailed regional population estimates. The NMDA believes, based upon their own survey efforts, that Knowles (1998) and Paternoster (1997) underestimated black-tailed prairie dog occupied habitat in New Mexico (DuBois, New Mexico Department of Agriculture, in litt. 1999).

The Service estimates that 39,000 acres (16,000 hectares) of black-tailed prairie dog occupied habitat occur in New Mexico. This estimate is based upon data provided by Paternoster (1997) for Roosevelt and Curry Counties; data provided by Sager (1996) and Sidle (U.S. Forest Service, in litt. 1999) for Colfax, Harding, Mora, and Union Counties; and for all other counties—(1) total county acreage, (2) species presence or absence by county as determined by Bodenchuck (1981), and (3) mean species occupancy rate by county as determined by Hubbard and Schmitt (1983).

Trends--Approximately 6 percent of the potential black-tailed prairie dog habitat in New Mexico has been converted to cropland (Table 2). Sylvatic plague also has likely caused declines in the State, most recently in the northeastern portion (Sager 1996). The States’ Draft Conservation Agreement notes that "there are no data available that would suggest populations in New Mexico are stable and/or improving" (Van Pelt in prep.).

Service Evaluation--The Service believes that black-tailed prairie dog occupied habitat in New Mexico has experienced significant historic declines. Following restrictions on toxicant use in 1972, increases in occupied habitat appear to have occurred (Table 1). However, the Service believes that declines in occupied habitat have occurred in recent years.

North Dakota

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat in the southwestern third of North Dakota, west of the Missouri River (Hall and Kelson 1959). Many large colonies of black-tailed prairie dogs were present in North Dakota west of the Missouri River in the early 1900’s (Bailey 1926). Presently, the species appears to be scattered throughout the same area with remnant populations on or near the Little Missouri National Grassland, Theodore Roosevelt National Park, and Standing Rock Reservation.

The Service estimates that approximately 44 percent of black-tailed prairie dog occupied habitat in North Dakota occurs on private and State lands, 40 percent on tribal lands, and 16 percent on Federal lands.

Abundance--Approximately 3 percent of black-tailed prairie dog occupied habitat in the United States may have existed in North Dakota historically (Table 2). Approximately 4 percent of occupied habitat in the United States currently exists in North Dakota (Table 1). Statewide estimates of occupied habitat noted in Table 1 for North Dakota range from 2 million acres (810,000 hectares) historically (Knowles 1998) to approximately 7,000 acres (2800 hectares) as a conservative estimate in 1973 (Grondahl 1973). The most recent estimate of occupied habitat is the Forest Service’s preliminary estimate of approximately 25,000 acres (10,000 hectares) (Sidle, U.S. Forest Service, pers. comm. 1999). The reduction in occupied habitat from historic times to present is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1961, 19,750 acres (8,000 hectares) of black-tailed prairie dog occupied habitat were estimated to occur in the State (Bureau of Sport Fisheries and Wildlife 1961). Grondahl (1973) reported 6,770 acres (2,740 hectares) of occupied habitat in 245 colonies; however, he noted that he "made a limited effort to locate prairie dog towns" and acreage was not determined for several colonies. Stockrahm (1979) estimated occupied habitat to be approximately 10,000 acres (4,000 hectares). The North Dakota Game and Fish Department conducted prairie dog surveys during 1980-1991 and counted 383 black-tailed prairie dog colonies in 11 counties totaling 20,464 acres (8,290 hectares) (North Dakota Game and Fish Department undated). Colony size ranged from 1 to 600 acres (0.41 to 243 hectares). A majority of the colonies (72 percent) were 50 acres (20 hectares) or less in size. Knowles (1998) estimated 20,444 acres (8,280 hectares) of occupied habitat for the species. The 1998 BFF Recovery Foundation telephone survey reported 15,160 acres (6,140 hectares) of black-tailed prairie dog occupied habitat in seven North Dakota counties; six counties within the species’ range did not respond (Black-footed Ferret Recovery Foundation in litt. 1998). Aerial surveys conducted in the State in 1999 as part of an ongoing work effort by the Forest Service provided a preliminary estimate of 25,000 acres (10,000 hectares) of occupied habitat in North Dakota (Sidle, U.S. Forest Service, pers. comm. 1999). McKenna (North Dakota Game and Fish Department, in litt. 1999) cites 30,000 acres (12,000 hectares) of occupied habitat in the State.

The only recent estimate of existing occupied habitat at a specific location is 2,862 acres (1,158 hectares) at Little Missouri National Grasslands (0.28 percent of Federal lands within Little Missouri National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999).

The Service believes that 25,000 acres (10,000 hectares) of black-tailed prairie dog occupied habitat (Sidle, U.S. Forest Service, pers. comm. 1999) is a reasonable Statewide estimate.

Trends--Approximately 53 percent of the potential black-tailed prairie dog habitat in North Dakota has been converted to cropland (Table 2). Historic declines in occupied habitat in the State were documented by Bishop and Culbertson (1976). They examined aerial photographs of western North Dakota from 1939 to1972 to evaluate the impact of control programs and land use practices on black-tailed prairie dog colonies on part of the Little Missouri National Grasslands. Colonies were measured for three periods during the 33-year span and showed an 89 percent decline in the number of colonies, and a 93 percent decline in the amount of occupied habitat. The NGFD believes that black-tailed prairie dog occupied habitat in the State increased from 10,000 acres (4,000 hectares) in the mid 1970’s to 30,000 acres (12,000 hectares) in 1999 (McKenna, North Dakota Game and Fish Department, in litt. 1999).

Service Evaluation--The Service believes that black-tailed prairie dog occupied habitat in North Dakota has experienced significant declines from historic estimates, but has likely been fairly stable to increasing in recent years (Figure 2). The amount of occupied habitat in North Dakota is relatively small compared to other States in the northern Great Plains.

Oklahoma

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout approximately the western two-thirds of Oklahoma west of the 97th meridian (Hall and Kelson 1959). Presently, the species is largely limited to the panhandle (Shaw et al. 1993, Tyler 1968, Wuerthner 1997), although other scattered remnant populations occur in the western half of the State outside of the panhandle (Shackford et al. 1990).

The Service estimates that approximately 90 percent of black-tailed prairie dog occupied habitat in Oklahoma occurs on private lands (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1998).

Abundance--Approximately 6 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Oklahoma historically (Table 2). Approximately 1 percent of occupied habitat in the United States currently exists in Oklahoma (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Oklahoma range from 950,000 acres (385,000 hectares) historically (Knowles 1998) to less than 8,600 acres (3,500 hectares) in 1998 (Lomolino, University of Oklahoma, in litt. 1999). This reduction in occupied habitat is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1961, approximately 15,000 acres (6,080 hectares) of black-tailed prairie dog occupied habitat were estimated to occur in Oklahoma (Bureau of Sport Fisheries and Wildlife 1961). Statewide surveys completed in 1966-1967 reported 9,522 acres (3,856 hectares) of occupied habitat (Tyler 1968). Lewis and Hassien (1973) estimated that 15,000 acres (6,080 hectares) of occupied habitat were present in 1973. Surveys in 1986-1989 reported approximately 18,000 acres (7,300 hectares) of occupied habitat (Shackford et al. 1990). The Oklahoma Department of Wildlife Conservation concurs with the estimate by Shackford et al. (1990) of 18,000 acres (7,300 hectares) of black-tailed prairie dog occupied habitat in the State (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1998). In 1990, Shaw et al. (1993) surveyed lands in the Oklahoma panhandle and estimated occupied habitat acreage at levels very similar to those in 1986-1989. However, in 1991-1992, these authors noted that several large complexes in Cimarron County experienced abrupt declines, presumably due to sylvatic plague (Figure 1). The 1998 BFF Recovery Foundation survey reported 70,000 acres (28,000 hectares) of black-tailed prairie dog occupied habitat in the State (Black-footed Ferret Recovery Foundation in litt. 1998), although one county estimate was 50,000 acres (20,000 hectares). Knowles (1998) estimated that less than 9,500 acres (3,850 hectares) remained in Oklahoma. Field surveys conducted by the University of Oklahoma as part of an ongoing study have found less than 8,600 acres (3,500 hectares) of occupied habitat in Oklahoma (Lomolino, University of Oklahoma, in litt.).

The only recent estimate of existing occupied habitat at a specific location is approximately 1,975 acres (800 hectares) for Cimarron County, the largest amount of occupied habitat for any Oklahoma county (Lomolino, University of Oklahoma, in litt. 1999).

The Service believes that approximately 9,000 acres (3,600 hectares) of black-tailed prairie dog occupied habitat (Lomolino, University of Oklahoma, in litt. 1999) is a reasonable Statewide estimate.

Trends--Approximately 69 percent of the potential black-tailed prairie dog habitat in Oklahoma has been converted to cropland (Table 2).

Recent occupied habitat trends have been well documented in Cimarron County, where most black-tailed prairie dog populations in Oklahoma occur (Figure 1). In 1967, occupied habitat was estimated to be 1,837 acres (744 hectares) (Tyler 1968). By 1972, occupied habitat increased to 5,500 acres (2,228 hectares) (Lewis and Hassien 1973); and by 1989, occupied habitat increased to 10,406 acres (4,214 hectares) (Shackford et al. 1990). In 1991, occupied habitat declined to 2,370 acres (960 hectares); and in 1992, very little occupied habitat was found (Shaw 1993). This decline was presumed due to sylvatic plague. In 1999, occupied habitat recovered somewhat to 1,975 acres (800 hectares) (Lomolino, University of Oklahoma, in litt. 1999). East of the State’s panhandle, occupied habitat has experienced a steady decline since the 1960’s (Shackford et al. 1990).

The ODWC believes that precise historic data is not available in Oklahoma, and, therefore, range reduction for the species cannot be documented. The ODWC believes that the species is broadly distributed across the State’s grasslands (90 percent on private land) and that numbers appear stable in the State; however, this contradicts ongoing work by Lomolino (University of Oklahoma, in litt. 1999) who reported less than 8,600 acres (3,500 hectares) for a Statewide total. In 1998, the ODWC documented additional prairie dog towns in the State, but did not report the amount of occupied habitat (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1999).

Service Evaluation--The Service believes that there have been significant declines from historic estimates of black-tailed prairie dog occupied habitat in Oklahoma. The panhandle has experienced significant declines in the past 10 years, with limited recovery. These declines were likely due to sylvatic plague. The remainder of occupied habitat in the State has experienced a slow, steady decline since the 1960’s. Overall, Oklahoma has less occupied habitat than any other State. Populations appear to have been reduced by 50 percent in the last 10 years.

South Dakota

Distribution--Historically, black-tailed prairie dogs 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. Known concentrations exist at Buffalo Gap National Grassland, Cheyenne River Sioux Tribe Reservation, Pine Ridge Reservation, and Rosebud Sioux Tribe Reservation.

The Service estimates that approximately 73 percent of black-tailed prairie dog occupied habitat in South Dakota occurs on tribal lands, 17 percent occurs on private (frequently adjoining tribal lands) and State lands, and 10 percent occurs on Federal lands.

Abundance--Approximately 8 percent of black-tailed prairie dog occupied habitat in the United States may have existed in South Dakota historically (Table 2). Approximately 22 percent of occupied habitat in the United States currently exists in South Dakota (Table 1). South Dakota has a significant portion of the remaining black-tailed prairie dog occupied habitat in the United States. Statewide estimates of occupied habitat noted in Table 1 for South Dakota range from greater than 1,757,000 acres (712,000 hectares) historically, following the initiation of intensive control efforts in 1918 (Linder et al. 1972), to 33,000 acres (13,000 hectares) 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 acres (60,000 hectares) (Sidle, U.S. Forest Service, pers. comm. 1999). This reduction in occupied habitat from historic times to the present is approximately 92 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1967, data based on aerial surveys and reports from South Dakota Department of Game, Fish and Parks indicated that about 37,000 acres (15,000 hectares) of black-tailed prairie dog occupied habitat existed in the State (Henderson et al. 1974). Rose (1973) estimated 60,000 acres (24,000 hectares) of occupied habitat in 1968. Tschetter (1988) noted 700,000 acres (284,000 hectares) of occupied habitat existed in 1980, but that this amount decreased to 184,000 acres (75,000 hectares) in 1987. He also noted that 76 percent of occupied habitat for the species occurred on tribal lands. Several sources estimated approximately 245,000 acres (99,000 hectares) of occupied habitat in the mid 1990’s (Knowles 1995, Knowles 1998, Mulhern and Knowles 1995). A 1998 phone survey estimated 175,000 acres (71,000 hectares) (Black-footed Ferret Recovery Foundation in litt. 1998). The SDGFP estimated 231,000 acres (94,000 hectares) of occupied habitat were present in 1996, based on a questionnaire/mail survey (South Dakota Department of Game, Fish, and Parks 1996). Aerial surveys completed in 1999 by the Forest Service provided a preliminary estimate of 147,000 acres (60,000 hectares) of black-tailed prairie dog occupied habitat in South Dakota (Sidle, U.S. Forest Service, pers. comm. 1999).

Recent estimates of existing occupied habitat at specific locations include approximately 45,000 acres (18,000 hectares) on Rosebud Sioux Tribal lands and an additional 25,000 acres (10,000 hectares) on adjoining lands (Finnegan et al., Rosebud Sioux Tribe, in litt. 1998), 44,000 acres (18,000 hectares) on the Cheyenne River Sioux Tribal and adjoining lands (Bourland and Dupris, Cheyenne River Sioux Tribe, in litt. 1998), 20,000-30,000 acres (8,000-12,000 hectares) on Pine Ridge Tribal lands (Yellowhair, Pine Ridge Sioux Tribe, pers. comm. 1999), and 13,270 acres (5,370 hectares) at Buffalo Gap National Grasslands (2.22 percent of Federal lands within Buffalo Gap National Grasslands) and 1,589 acres (643 hectares) at Grand River National Grasslands (1.03 percent of Federal lands within Grand River National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999). The Crow Creek Sioux Tribe estimates that "60 active grounds" of black-tailed prairie dogs exist on their tribal lands (Miller, Crow Creek Sioux Tribe, in litt. 1998).

The Service believes that 147,000 acres (60,000 hectares) of black-tailed prairie dog occupied habitat (Sidle, U.S. Forest Service, pers. comm. 1999) is a reasonable Statewide estimate.

Trends--Approximately 43 percent of the potential black-tailed prairie dog habitat in South Dakota has been converted to cropland (Table 2). Black-tailed prairie dog occupied habitat in South Dakota has experienced significant declines from historic estimates. There appeared to be declines in occupied habitat until 1961, then recovery until the 1980’s when occupied habitat again declined. Reductions in occupied habitat in South Dakota appear to be primarily in response to control efforts, as well as some loss in available habitat due to cropland development. Sylvatic plague has not been documented in black-tailed prairie dogs in the State.

Service Evaluation--The Service believes that there have been significant declines from historic estimates of black-tailed prairie dog occupied habitat in South Dakota, with notable recovery from 1961 to 1980. Thereafter, extensive control efforts at Pine Ridge Reservation, on Forest Service managed lands, and elsewhere in the 1980’s resulted in a significant decline in occupied habitat (Figure 1). Subsequently, occupied habitat has remained fairly stable (Figure 2). South Dakota appears to have more black-tailed prairie dog occupied habitat than any other State with most populations occurring on tribal land. Additionally, more unoccupied but available habitat appears to remain in South Dakota than in other States.

Texas

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout the northwestern one-third of Texas (Bailey 1905, Hall and Kelson 1959). Presently, the species occurs largely in the western portion of the northern panhandle, with Dallam and Deaf Smith Counties having the greatest amount of occupied habitat (Lair and Mecham 1991). Some scattered remnant populations exist in the Trans-Pecos Region of western Texas.

The Service estimates that approximately 99 percent of black-tailed prairie dog occupied habitat in Texas occurs on private and State lands and 1 percent occurs on Federal lands.

 

Abundance--Approximately 21 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Texas historically (Table 2). Approximately 11 percent of occupied habitat in the United States currently exists in Texas (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Texas range from 58 million acres (23 million hectares) historically (Bailey 1905) to 23,000 acres (9,000 hectares) at present (Knowles 1998). This reduction in occupied habitat is greater than 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1961, black-tailed prairie dog occupied habitat in Texas was estimated at 26,000 acres (11,000 hectares) (Bureau of Sport Fisheries and Wildlife 1961). In 1965, Cottam and Caroline (1965) estimated more than 12,900 acres (5,200 hectares) of occupied habitat were present in the State.

In 1977, approximately 90,000 acres (36,000 hectares) of habitat were estimated to exist in Texas, largely in the northern panhandle region (Cheatheam 1977). In this study, most colonies were located from aerial photographs of 108 counties; other colonies were located through individual contacts. The author noted that on-site inspection of 229 colonies (approximately 20 percent of the 1,144 colonies located by aerial photographs) found 45 colonies totaling 6,550 acres (2,650 hectares) that were inactive, that 13 colonies had decreased by a total of 1,685 acres (682 hectares), and that 30 colonies had increased by a total of 4,524 acres (1,831 hectares). These changes equate to a net loss of 3,709 acres (1,501 hectares) in the 229 colonies. If the 229 colonies receiving an on-site inspection were typical of all colonies located from aerial photographs, occupied habitat was actually 24 percent, or 18,545 acres (7,505 hectares), less in the area surveyed by aerial photographs. Accordingly, the total occupied habitat would have been approximately 71,479 acres (28,927 hectares).

In 1991, Lair and Mecham (1991) inventoried black-tailed prairie dog towns greater than 100 acres (40 hectares) for the purpose of locating black-footed ferret habitat within Texas. Consequently, not all towns in the State were included. Twenty-nine counties in the Texas panhandle were examined. County to county comparisons with Cheatheam (1977) were not possible. Approximately 68,000 acres (28,000 hectares) of occupied habitat were reported. The Texas Parks and Wildlife Department believes that the two studies, Cheatheam (1977) and Lair and Mecham (1991), are not comparable because the latter estimate covered a smaller area and reported minimum estimates (Sansom, Texas Parks and Wildlife Department, in litt. 1998).

The BFF Recovery Foundation’s 1998 telephone survey estimated 227,000 acres (92,000 hectares) of occupied habitat for the species (Black-footed Ferret Recovery Foundation in litt. 1998), although one county estimate was 100,000 acres (40,000 hectares). Knowles (1998) estimated 23,000 acres (9,000 hectares) of occupied habitat in Texas.

The only recent estimate of existing occupied habitat at a specific location is 966 acres (391 hectares) in Rita Blanca National Grasslands (1.04 percent of Federal lands within Rita Blanca National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999).

The Service believes that 71,000 acres (29,000 hectares) of black-tailed prairie dog occupied habitat, modified from Cheatheam (1977), is a reasonable Statewide estimate.

Trends--Approximately 28 percent of the potential black-tailed prairie dog habitat in Texas has been converted to cropland (Table 2). Additionally, sylvatic plague has impacted the species in the State (Sager 1996). The TPWD agrees that "the numbers and habitat of the species have been radically reduced in Texas." However, it does not agree with the current estimate of 23,000 acres (9,000 hectares) occupied habitat from Knowles (1998) (Sansom, Texas Parks and Wildlife Department, in litt. 1998).

Service Evaluation--The Service believes that there have been significant declines from historic estimates of black-tailed prairie dog occupied habitat in Texas. However, based upon the limited amount of information available, the Service believes that following the restrictions on toxicants use in 1972, occupied habitat increased. The Service also believes that populations may have remained fairly stable since the late 1970’s.

Wyoming

Distribution--Historically, black-tailed prairie dogs occurred on suitable habitat throughout the eastern half of Wyoming, 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, remnant populations appear to be scattered throughout the same area, with known concentrations on and near Thunder Basin National Grassland in the northeastern portion of the State.

The Service estimates that approximately 86 percent of black-tailed prairie dog occupied habitat in Wyoming occurs on private and State lands and 14 percent occurs on Federal lands.

Abundance--Approximately 7 percent of black-tailed prairie dog occupied habitat in the United States may have existed in Wyoming historically (Table 2). Approximately 18 percent of occupied habitat in the United States currently exists in Wyoming (Table 1). Statewide estimates of occupied habitat noted in Table 1 for Wyoming range from 16 million acres (6.5 million hectares) historically (Knowles 1998) to 49,000 acres (20,000 hectares) in 1961 (Bureau of Sport Fisheries and Wildlife 1961). The most recent estimate is 70,000-180,000 acres (28,000-73,000 hectares) in 1998 (Knowles 1998). This reduction in occupied habitat from historical times to the present is approximately 99 percent. A comparison between historic occupied habitat as estimated by Table 2 and the Service estimate of current occupied habitat (Table 1) indicates a similar trend.

In 1971, Clark (1973) estimated approximately 133,000 acres (54,000 hectares) of black-tailed prairie dog occupied habitat in Wyoming. Following field mapping in 1987, the Wyoming Game and Fish Department estimated 131,000-204,000 acres (53,000-83,000 hectares) of occupied habitat in the State (Oakleaf et al. 1996). The BFF Recovery Foundation phone survey estimated 535,000 acres (217,000 hectares) of occupied habitat for both species of prairie dogs in Wyoming (Black-footed Ferret Recovery Foundation in litt. 1998). Based upon species breakdowns by county presented by Clark (1973), approximately 422,000 acres (171,000 hectares) of black-tailed prairie dog habitat were noted by BFF Recovery Foundation. The Wyoming Department of Agriculture requested that officials from county Weed and Pest Districts in Wyoming provide estimates of the number of acres occupied by black-tailed prairie dog within their counties (Micheli, Wyoming Department of Agriculture, in litt. 1999). A total of 362,000 acres (147,000 hectares) were estimated to be occupied by black-tailed prairie dogs in the State. The WDA states that these estimates are conservative, realistic, and based on firsthand observations by local officials who have spent years inspecting their counties for weeds and pests. The WDA estimates over 100 million black-tailed prairie dogs exist in the State, based upon an estimate of 30 prairie dog holes per acre and 10 dogs per hole (Micheli, Wyoming Department of Agriculture, in litt. 1998, 1999). This estimate equates to a density of 300 black-tailed prairie dogs per acre (741 per hectare) which far exceeds density estimates in available literature references (Fagerstone and Ramey 1996, Hoogland 1995, King 1955, Koford 1958, Miller 1996).

The only recent estimate of existing occupied habitat at a specific location is 18,239 acres (7,381 hectares) at Thunder Basin National Grasslands (3.26 percent of Federal lands within Thunder Basin National Grasslands) (Sidle, U.S. Forest Service, in litt. 1999), which, in the absence of sylvatic plague, has experienced increases in recent years.

The Service estimates 125,000 acres (51,000 hectares) of black-tailed prairie dog occupied habitat exist in Wyoming. This figure represents a 25 percent decline from the mid-point of the 1987 WGFD estimate of 131,000-204,000 acres (53,000-83,000 hectares). This projected decline during the last 12 years for Wyoming is less than the Statewide decline of 50 percent for the adjacent State of Montana during the last 12 years, where sylvatic plague impacts have been more apparent than in Wyoming. Lockhart (U.S. Fish and Wildlife Service, in litt. 1998) and Jennings (U.S. Fish and Wildlife Service, pers. comm. 1999) note sylvatic plague impacts in black-tailed prairie dog complexes throughout the State. However, at least one large complex, Thunder Basin National Grassland, has not been impacted by sylvatic plague and has experienced significant increases in occupied habitat (High Country News, 1999).

Trends--Approximately 12 percent of the potential black-tailed prairie dog habitat in Wyoming has been converted to cropland (Table 2). In regard to black-tailed prairie dog populations, the WGFD "believes there has been a significant decline in Wyoming since the turn of the century" and believes "the potential exists for continued declines." The WGFD also notes that many of these populations are "small, disjunct, and isolated" (Wichers, Wyoming Game and Fish Department, in litt. 1998).

Service Evaluation--The Service believes that there have been significant declines from historic estimates of black-tailed prairie dog occupied habitat in Wyoming. Increases in occupied habitat occurred following restrictions in toxicant use in 1972; however, the Service believes that recent declines are likely to continue, largely due to impacts from sylvatic plague.

2.4.6.2 Canada.

Distribution--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 in extreme southern Saskatchewan. Many of these colonies are in Canada’s Grasslands National Park (Laing 1986).

Abundance--Canada represents a very small percentage (approximately 0.3 percent) of the rangewide population (Table 1). Millson (1976) noted that in 1970 there were 15 colonies in this area totaling 1,244 acres (503 hectares); and in 1975, he mapped 16 colonies totaling 1,885 acres (763 hectares). Laing (1986) later mapped 14 colonies totaling 1,691 acres (685 hectares). Knowles (1998) estimated that there are 1,500-2,000 acres (600-800 hectares) of black-tailed prairie dog occupied habitat in Canada. Surveys conducted between 1993 and 1996 found 25 colonies totaling 2,318 acres (938 hectares), with 13 colonies totaling 1,353 acres (548 hectares) located within Canada’s Grasslands National Park holdings (Fargey, Grasslands National Park, pers. comm. 1998). Colonies ranged from 3.9 acres (1.57 hectares) to 328 acres (132.9 hectares). There are no other known colonies in Canada.

Trends--Black-tailed prairie dog occupied habitat in Canada has always been limited, but appears to have remained fairly constant.

Service Evaluation--The Service believes that black-tailed prairie dog occupied habitat in Canada is approximately 2,000 acres (800 hectares) and, in the absence of sylvatic plague, will likely remain stable.

2.4.6.3 Mexico.

Distribution--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.

Abundance--Historically, black-tailed prairie dog occupied habitat in Mexico was estimated at 1,384,000 acres (560,000 hectares) (Mearns 1907 as cited in Ceballos et al. 1993). Ceballos et al. (1993) mapped 136,000 acres (55,000 hectares) of occupied habitat in Chihuahua, Mexico, in 1988. Included in this estimate was one colony within the Janos-Nuevo Casas Grandes Complex which totaled 86,360 acres (34,949 hectares). List et al. (1997) reported the total amount of occupied habitat in Mexico as 90,000 acres (36,000 hectares) in 1996. The Janos-Nuevo Casas Grandes Complex is currently the largest black-tailed prairie dog complex in North America and contains approximately 12 percent of all occupied habitat rangewide (Table 1). This complex is the only significant black-tailed prairie dog population remaining in Mexico (Ceballos et al. 1993).

The Service believes that 90,000 acres (36,000 hectares) from List et al. (1997) is a reasonable current estimate of black-tailed prairie dog occupied habitat in Mexico.

 

Trends--From 1988 to 1996, the geographic range of the species in Mexico contracted 79 percent and the amount of occupied habitat decreased by 34 percent (List et al. 1997). Ceballos et al. (1993) and List et al. (1997) noted historic and recent declines at the Janos-Nuevo Casas Grandes Complex. Colony fragmentation has occurred in black-tailed prairie dog colonies previously surveyed, reducing the size of towns and increasing their isolation. The average town size reduced from 6,323 acres (2,559 hectares) in 1988 to 418 acres (169 hectares) in 1996 (List et al. 1997). He indicated that reduction was due to increased cropland conversion, control, and drought.

These same factors have impacted the Mexican prairie dog, a peripheral isolate of the black-tailed prairie dog, which is currently classified as endangered (Trevino-Villarreal and Grant 1998). The Mexican prairie dog occurs principally in the State of Nuevo Leon approximately 600 miles (1,000 kilometers) southeast of the black-tailed prairie dog complex in Chihuahua, Mexico. Habitat destruction has been considered one of the most important factors in the recent decline of the Mexican prairie dog, which currently inhabits 118,000 acres (48,000 hectares). The black-tailed prairie dog currently occupies approximately 90,000 acres (36,000 hectares) in Mexico. These two species appear to be declining for similar reasons.

Service Evaluation--The Service believes that black-tailed prairie dog occupied habitat in Mexico has declined significantly from historic estimates and that this decline continues (Figure 1). This decline appears to be due primarily to cropland conversion.