12-MONTH ADMINISTRATIVE FINDING, BLACK-TAILED PRAIRIE DOG
Chapter 3 - Table of Contents
3. FACTORS AFFECTING THE SPECIES - TABLE OF CONTENTS
3.1 The Present or Threatened Destruction, Modification, or Curtailment of the Species Habitat or Range
3.1.1 Habitat Loss Due to Cropland Development
3.1.2 Habitat Loss Due to Urban Development
3.1.3 Habitat Loss Due to Changes in Vegetative Communities
3.1.4 Habitat Loss Due to Structural Deterioration of Burrows
3.1.5 Habitat Fragmentation and Its Indirect Exacerbating Influence on the Effects of Other Factors
3.1.6 Overall Threat of Present or Threatened Destruction, Modification, or Curtailment of the Species Habitat or Range
3.2 Overutilization for Commercial, Recreational, Scientific, or Educational Purposes
3.2.1 Commercial Interest in the Species as a Pet
3.2.2 Recreational Shooting of the Species
3.2.3 Overall Threat of Overutilization for Commercial, Recreational, Scientific or Educational Purposes
3.3 Disease or Predation
22.214.171.124 Extent of Plague
126.96.36.199 Effects of Epizootics on Populations
3.3.3 Overall Threat of Disease or Predation
3.4 The Inadequacy of Existing Regulatory Mechanisms
3.4.6 Overall Threat of Inadequacy of Existing Regulatory Mechanisms
3.5 Other Natural or Manmade Factors Affecting the Species Continued Existence
3.5.1 Rodent Control
188.8.131.52 Rodent Control Efforts Prior to 1972
184.108.40.206 Recent Rodent Control Efforts
3.5.2 Synergistic Effects
3.5.3 Overall Threat of Other Natural or Manmade Factors Affecting the Species Continued Existence
3.6 Vulnerability of the Species in Perspective
3.6.1 Vulnerability of Complexes
3.6.2 Area Evaluations
12-MONTH ADMINISTRATIVE FINDING, BLACK-TAILED PRAIRIE DOG
3. FACTORS AFFECTING THE SPECIES
Section 4(a)(1) of the Act and regulations (50 CFR, Part 424), promulgated to implement listing provisions of the Act, set forth the procedures for adding species to the Federal endangered and threatened species list. Listing decisions may consider any one or any combination of the five factors listed in section 4(a)(1). All of these factors act both alone and in concert to affect the status of the black-tailed prairie dog.
Three major impacts have had a substantial influence on black-tailed prairie dog populations. Although they have overlapped in different time periods, their principal influences occurred as described hereafter. The first major impact on the species was the initial conversion of prairie grasslands to cropland in the eastern portion of its range from approximately the 1880s through the 1920s. The conversion of native prairie to cropland likely reduced black-tailed prairie dog occupied habitat in the United States from about 80 million acres (32 million hectares) to about 50 million acres (20 million hectares) or less. This estimate of prairie conversion is extrapolated from Laycocks (1987) estimate of 104 million acres (42 million hectares) converted from 1880-1899, assuming that 20 percent of this was black-tailed prairie dog occupied habitat (Whicker and Detling 1988) and that the rate of decline in the next 20 years was 50 percent of that in the preceding 20 years. The second major impact on the species was large-scale control efforts conducted from approximately 1918 to approximately 1972 in efforts to reduce competition between prairie dogs and domestic livestock. Large scale, repeated control efforts likely reduced black-tailed prairie dog occupied habitat in the United States from about 50 million acres (20 million hectares) to approximately 400,000 acres (162,000 hectares) by 1961 (Bureau of Sport Fisheries and Wildlife 1961). Some limited recovery and subsequent declines have since occurred in these remnant populations. The third major impact on the species was the inadvertent introduction of an exotic disease, sylvatic plague, from the Old World into North American ecosystems around 1900, with the first recorded impacts on the black-tailed prairie dog in 1946. The influence of sylvatic plague on black-tailed prairie dog populations is recent in a historical sense, and especially in a biological sense. Its influence may have been masked by other factors, but it has had significant depressant effects on remnant populations in the last 10-15 years. These three factors, as well as other additional factors impacting the species, are discussed below.
3.1 THE PRESENT OR THREATENED DESTRUCTION, MODIFICATION, OR CURTAILMENT OF THE SPECIES HABITAT OR RANGE
Significant destruction, modification, and curtailment of black-tailed prairie dog habitat and range have occurred. The aftermath of some of these influences is apparent, e.g., intensively farmed croplands, while other influences such as habitat deterioration are not as obvious. The indirect effects of previous habitat modifications may have less apparent but significant influences on black-tailed prairie dog populations.
3.1.1 Habitat Loss Due to Cropland Development
The eastern portion of the historic range of the black-tailed prairie dog includes a large portion of the most productive cropland in the United States. Between 1880 and 1899, 104 million acres (42 million hectares) on the Great Plains were converted to crop production (Laycock 1987). Conversion of native prairie continued throughout the early 1900s until the dust bowl of the 1930s, when the conversion of submarginal land and drought conditions caused severe land degradation. Some of these lands were subsequently returned to grasslands with native species and are presently managed by the Forest Service as National Grasslands. Native grasslands in the North American mid-continent have been much reduced. In the United States, approximately 33 percent of the historic range of the black-tailed prairie dog and 37 percent of the suitable habitat within its range has been converted to cropland uses at present (Black-footed Ferret Recovery Foundation, in litt. 1999, Table 2). This fundamental land use change resulted in significant destruction of black-tailed prairie dog habitat, mostly in the eastern portions of the species range where adequate precipitation favored farming. Cropland conversion was so thorough as to curtail the range of the species in the eastern part of some midwestern States where conversion to cropland has been essentially complete.
The present threat of large-scale destruction of black-tailed prairie dog habitat through cropland conversion is much less than in the early days of agricultural development in the Great Plains, except perhaps in Mexico. For example, in Nebraska, rangeland continues to be converted to cropland and other uses, but at a slower pace than previously (Amack, Nebraska Game and Parks Commission, in litt. 1998). This difference is due to the fact that land with the highest potential for traditional farming uses was converted many years ago.
Cropland conversion of black-tailed prairie dog occupied habitat continues today, but it is unknown how much is converted annually. Improved dryland farming techniques have been responsible for additional cropland conversion in the western Great Plains in recent years. Conversion of rangelands and prairie habitat to cropland occurs in some areas due to continuing improvements in intensive agricultural techniques, e.g., dryland wheat farming in Montana (Knowles et al. 1996, Lessica 1995) and irrigated croplands in Mexico (List et al. 1997). List et al. (1997) reported that occupied black-tailed prairie dog habitat in Mexico declined by 34 percent between 1988 and 1996, in part due to rangeland conversion due to farming. A primary cause of reduction of prairie dog habitat in Kansas is conversion of short grass prairie to cropland or other uses (Williams, Kansas Department of Fish and Wildlife, in litt. 1998).
Prairie conversion to cropland in the western portion of South Dakota has been facilitated, in part, by the development of genetically-altered soybeans that can be cultivated on lands previously suitable only as rangeland. The use of recombinant genetic techniques to develop drought-resistant crop strains may further curtail the habitat of the black-tailed prairie dog if additional or existing varieties become more widely used (Hogan, U.S. Fish and Wildlife Service pers. comm. 1998). Hexem and Krupa (1987) identified 57.7 million acres (23 million hectares) of unplowed land in the western Great Plains with high to medium potential for cropland conversion by the year 2000. If a major portion of these lands was converted to cropland, it would result in a significant reduction in native prairie and would likely adversely affect the black-tailed prairie dog.
Some comment letters noted that the Conservation Reserve Program (CRP) has slowed the trend of rangeland conversion to farming. However, Stutzman (1989) reported that in five counties in north-central Montana, 56,000 acres (23,000 hectares) of native prairie were converted to cropland between 1987 and 1989, despite the CRP. Lesica (1995) noted that in the past 10 years there has been a small decline in the amount of cropland in Montana, due mainly to the CRP. However, the author also believes that the CRP has encouraged the loss of native prairie in Montana. The CRP allowed operators to break up native prairie and put it into crops at the same time that they have enrolled cropland in CRP. More land was put back into grass than was broken, but less than 6 percent of CRP land in Montana was planted to native species. Knowles et al. (1996) noted in Montana that Agropyron cristatum (crested wheatgrass) was the most common species planted on lands enrolled in the CRP, with a resultant loss in grassland biodiversity. Grass species established on most CRP lands would not likely be conducive for occupancy by black-tailed prairie dogs.
Some degree of prairie conversion to cropland is likely to continue (Soil Conservation Service 1989). Farming activities are expanding throughout the western Great Plains and will likely affect some remaining black-tailed prairie dog populations, although the magnitude of potential losses to the species habitat is unknown. Paternoster (1997) noted that most prairie dog colonies surveyed in New Mexico were bordered by agricultural lands that appeared to restrict colony expansion. Small isolated colonies surrounded by agriculture also were typical in Nebraska in aerial surveys in 1996 and 1997 (Sidle, U.S. Forest Service, pers. comm. 1998).
The Service believes that impacts on the species due to habitat loss via cropland conversion are a moderate threat to the species at present. In particular, black-tailed prairie dog occupied habitat in Mexico may continue to decline due to a more rapid rate of habitat conversion than is occurring in other portions of the species range.
3.1.2 Habitat Loss Due to Urban Development
One example of the present and threatened destruction of black-tailed prairie dog occupied habitat due to urban development near large cities is apparent along the Front Range of Colorado near Denver. In the early 1990s, 42,500 acres (17,200 hectares) of occupied habitat were mapped in the Denver/Boulder/Fort Collins metropolitan area (Skiba, Colorado Division of Wildlife, pers. comm. 1999). However, since the initial mapping effort, Knowles (1998) estimated that occupied habitat in this area has declined by approximately 8,000 acres due to urbanization. Several local organizations are actively acquiring and conserving black-tailed prairie dog habitat in response to wildlife conservation concerns of the local populace (The Denver Post 1998).
Although some black-tailed prairie dog occupied habitat has been lost due to urban development along the Front Range, an evaluation of the specific impact due to this factor is difficult because sylvatic plague also has significantly affected populations in this area in recent years (Weber, Colorado Division of Wildlife, pers. comm. 1998). Seery (U.S. Fish and Wildlife Service, pers. comm. 1998) estimates that occupied habitat mapped in the early 1990s in north central Colorado has been reduced by 50 percent due to various factors including urban development, but primarily due to sylvatic plague.
One type of area conducive to black-tailed prairie dog use in Colorado lies at the interface between urban areas and active croplands. The species persists precariously in heavily developed areas and is often persecuted via control in agricultural areas; however it prospers temporarily at the edge formed between these two land uses where speculative opportunities for additional development exist, but no active use occurs. Generally, urban development might not be considered a potential major influence on the species, since the species range is very large and since there are few large cities within its range. However, it has been noted that black-tailed prairie dogs are common in the urban front-range area west of Interstate 25 in Colorado (Kahn, Colorado Division of Wildlife, in litt. 1998). Interstate 25 is the major north-south transportation corridor and the focus of continuing rapid development in the State. In 1994, Colorado reported 42,500 acres (17,200 hectares) of occupied habitat (Skiba, Colorado Division of Wildlife, pers. comm. 1999) along the front range that could be affected by urbanization via habitat loss, fragmentation, dispersal limitations, etc. This portion of occupied habitat in Colorado appears to be a significant percentage of occupied habitat present in the State. Moreover, the most densely populated area of the species range in Colorado appears to be in areas with this type of land use. Most rangeland areas in Colorado have present occupancy rates of 0.32-0.5 percent (Sidle, U.S. Forest Service, in litt. 1999), while the front-range metropolitan area has occupancy rates of 1.6-3.1 percent (Seery, U.S. Fish and Wildlife Service, pers. comm. 1998; Skiba, Colorado Division of Wildlife, pers. comm. 1999). Urbanization also represents a locally significant loss of black-tailed prairie dog habitat in metropolitan areas near Wichita, Kansas and Helena, Montana (Knowles 1995).
The impact of urban development elsewhere in the species range is unknown. The influence of urban development on black-tailed prairie dog populations is likely cumulative with other factors; it may have a significant direct effect in a local area through the effects of habitat destruction and fragmentation.
The Service believes that overall impacts on the species due to habitat loss from urban development are a low threat at present.
3.1.3 Habitat Loss Due to Changes in Vegetative Communities
Habitat modification and loss due to the absence of black-tailed prairie dogs can be anticipated in the prairie ecosystem where populations have been extirpated or significantly reduced in number. Weltzin et al. (1997) determined that black-tailed prairie dogs, and the herbivores and granivores associated with their colonies, probably maintained grassland and savanna historically by preventing woody species such as mesquite from establishing or attaining dominance. List et al. (1997) reported that control of black-tailed prairie dogs in Mexico resulted in the invasion of mesquite shrubs that rendered the landscape unsuitable for reoccupation by the species; moreover, fire suppression would likely maintain this situation. Davis (1974) also noted that the removal of the species from some sites in Texas resulted in the invasion of brush. Arizona stated that grassland (prairie dog) habitat is "declining at an alarming rate" in Arizona (Shroufe, Arizona Game and Fish Department, in litt. 1998). It noted a 35 percent reduction in grassland habitat along the San Pedro River to mesquite woodland invasion that could be due to the cumulative effects of fire suppression, grazing practices and perhaps the elimination of the black-tailed prairie dog.
The fragmented nature of remaining prairie dog colonies, barriers to immigration and emigration, and the lack of fire and native ungulate herds that historically denuded the landscape and provided opportunities for prairie dog colonies to expand (Miller et al. 1994) accentuate habitat loss due to vegetative succession. The reduction of grazing pressure to achieve higher stands of grass around black-tailed prairie dog colonies is a management tool for restricting the expansion of colonies (Snell and Hlavachick 1980, Snell 1985, Uresk et al. 1981). It would appear that these types of land use changes can have an impact on black-tailed prairie dog occupancy as well. The degree to which this type of grassland change and other landscape alterations affect black-tailed prairie dog populations across their range is unknown. Nevertheless, these subtle habitat changes may be a major factor in the utilization of habitat or recolonization of former habitat by the species.
The Service believes that impacts on the species due to habitat loss from changes in vegetative communities are a moderate threat at present.
3.1.4 Habitat Loss Due to Structural Deterioration of Burrows
Physical habitat changes may limit population recovery where control, sylvatic plague, or other factors have removed black-tailed prairie dogs. Once the species no longer inhabits an area, the deterioration of its burrows may preclude recolonization, especially where light grazing pressure or mesic conditions do not favor the expansion of colonies. Prairie dog burrows can be used and maintained by many generations of animals, depending on burrow longevity due to local soil type. Once underground burrows collapse due to the effects of weathering and age, the species is less likely to reoccupy them and reestablish itself in an area. The collective effort of several generations in developing a burrow complex is not easily duplicated by a pioneering individual from another colony. Black-tailed prairie dogs seldom disperse further than 3 miles (5 kilometers) and generally migrate to another colony or the perimeter of their natal colony rather than establish a new colony (Garrett and Franklin 1988, Hoogland 1995). This phenomenon was evident at the Rocky Mountain Arsenal National Wildlife Refuge in Colorado where reintroduced black-tailed prairie dogs reestablished themselves quickly where intact burrows constructed by previous prairie dog populations (extirpated by sylvatic plague) had not deteriorated. However, prairie dogs established themselves slowly and with much less success where burrows had deteriorated (Seery, U.S. Fish and Wildlife Service, pers. comm. 1998).
The Service believes that impacts on the species due to habitat loss from burrow deterioration are a moderate threat at present.
3.1.5 Habitat Fragmentation and Its Indirect Exacerbating Influence on the Effects of Other Factors
The grassland biome in North America has suffered among the most extensive fragmentation and transformation of any biome on the continent (Groombridge 1992). More fragmented, more isolated, and less connected populations usually have higher extinction rates (Clark 1989, Gilpin and Soule 1986, MacArthur and Wilson 1967, Shaffer 1981, Wilcove et al. 1986, Wilcox and Murphy 1985). List et al. (1997) suggested that fragmented black-tailed prairie dog colonies in Mexico were prone to extirpation.
Across their range, many black-tailed prairie dog colonies are small and spatially isolated from other colonies (Miller et al. 1996). The BFF Recovery Foundation (1999) analyzed the most recent GIS data for black-tailed prairie dog colonies in Montana and found that 33 percent of the colonies were 10 acres (4 hectares) or less in size and 84 percent were less than 100 acres (40 hectares) or less in size. However, BFF Recovery Foundation also noted spatially associated colonies with sufficient interaction to maintain some biological relationships. This situation might not exist in areas where more cropland conversion or urban development have occurred and created barriers to movement.
Vanderhoof and Robel (1992) reported that although prairie dog colonies in Kansas increased in number by 28 percent between 1972 and 1991, the total occupied habitat declined by 19 percent. This suggests that formerly large single colonies had been broken up into numerous smaller colonies as a result of habitat fragmentation. Reports from Kansas (Powell 1992), Nebraska (U.S. Forest Service 1998), New Mexico (Sager 1996, Paternoster 1997), North Dakota (North Dakota Game and Fish Department, undated), Oklahoma (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1998), Wyoming (Wichers, Wyoming Game and Fish Department, in litt. 1998), and Mexico (List et al. 1997) confirm a trend toward smaller, more isolated colonies.
Miller et al. (1996) described existing prairie dog populations as small, disjunct, and geographically isolated. He further described the discontinuous nature of remaining populations as widely separated islands where habitat fragmentation has resulted in an increased likelihood of extinction for individual colonies due to genetic inbreeding and random demographic events. Dispersal movements that previously offset these adverse effects have been limited by barriers created by human development that preclude immigration or emigration. Fragmentation and extirpation of small, isolated colonies will result in the loss of additional genotypes, as occurred with the complete extirpation of the species in portions of the eastern and southwestern areas of its historic range. Lost genetic diversity will inherently be detrimental to the species.
Fragmentation of habitat threatens black-tailed prairie dog populations by(1) reducing the number and size of colonies which increases the likelihood of colony extinction through disease, genetic inbreeding, random demographic events, or natural environmental catastrophes; (2) widespread dispersion of colonies which limits or prevents ready repopulation by immigration; and (3) fostering habitat alterations between islands of remaining habitat which can present barriers to immigration of individuals that would otherwise repopulate extirpated colonies. If these isolated populations or metapopulations are extirpated for whatever reason in a highly fragmented landscape, then recolonization may not be possible given the limited migration reported by Garrett and Franklin (1988) and Hoogland (1995). The precise means by which these inter-related phenomena are affecting black-tailed prairie dog populations is unknown.
Gilpin (University of California at San Diego, pers. comm. 1999) suggests that various threats may interact to accelerate decline in black-tailed prairie dog populations. He also suggests that the current ecological situation for the species is quite different than what it was during the species evolutionary history. He believes that selection pressures have changed radically, and that populations may become no longer suited to their natural ecology. He notes that most populations are genetically isolated and subject to genetic erosion due to drift. He also notes that a sylvatic plague frequency of more than once per decade may be lethal to an isolated population.
The Service believes that impacts on the species due to habitat fragmentation are a moderate threat at present.
3.1.6 Overall Threat of Present or Threatened Destruction, Modification, or Curtailment of the Species Habitat or Range
Overall, the Service believes that this factor is a moderate threat to the species at present.
3.2 OVERUTILIZATION FOR COMMERCIAL, RECREATIONAL, SCIENTIFIC, OR EDUCATIONAL PURPOSES
3.2.1 Commercial Interest in the Species as a Pet
Herron (Texas Parks and Wildlife Department, pers. comm. 1999) and others have reported that black-tailed prairie dogs are removed from the wild for sale as pets. Herron was aware of three commercial operators who collectively removed approximately 5,000 individuals from the Texas panhandle and other States annually in recent years, although these efforts may have declined this past year. One animal export company in Texas noted that over the past 4 years their company has bought and sold approximately 20,000 black-tailed prairie dogs, largely from the same locations in western and northwestern Texas (Shaw, Texas Animal Export, in litt. 1999). Texas has initiated a requirement for reports from these parties. Miscellaneous reports indicate that this practice occurs elsewhere in the species range, but the extent of removal of individuals from the wild for use as pets is unknown.
The Service believes that impacts on the species due to the removal of individuals from the wild for use as pets is not a threat at present because of the small number of animals involved.
3.2.2 Recreational Shooting of Species
One factor impacting black-tailed prairie dog populations in some local areas is recreational (sport or varmint) shooting. At present, the Service does not believe that this factor is responsible for significant rangewide declines in the species population; however, it may be important locally. The popularity of that type of shooting has increased appreciably in recent years. However, the number of shooters in a given complex can fluctuate substantially from year to year. High-powered rifles with high-quality scopes enable the modern varmint shooter to be accurate at distances of up to 400 yards (366 meters) or greater, and many animals may be shot by an individual shooter each day (Kayser 1998). Many States do not require hunting licenses and have no bag limits or seasonal restrictions for taking prairie dogs. Additionally, the practice of leaving carcasses in the field when shooting prairie dogs complicates the potential of enforcing bag limits.
Knowles (1988) reported that shooting on two black-tailed prairie dog colonies removed 69 percent of the adults. He thought that the reduction of prairie dog populations below a certain threshold number might have a further negative consequence because fewer prairie dogs were available to watch for predators and keep the vegetation clipped around burrows to improve detection of predators. Vosburgh (1996) reported that intensive shooting can have a statistically significant impact on the density of local black-tailed prairie dog colonies. He observed that during the summer species density declined 33 percent on colonies with shooting and 15 percent on colonies without shooting. Prairie dogs also spent more time in alert postures and less time foraging on colonies where shooting occurred.
Extensive shooting, especially of pregnant females or females nursing young, could significantly reduce annual recruitment and change the ultimate population dynamics of a colony. In recent years, shooters have removed thousands of black-tailed prairie dogs annually from colonies on Forest Service National Grasslands in South Dakota and Wyoming. Thousands of shooter days (one individual shooting for a period of 1 day equals one shooter day) are focused on small areas in these situations. In one instance, the Forest Service District Ranger for the Conata Basin area of the Buffalo Gap National Grasslands in South Dakota estimated that shooters removed most of the young-of-the-year with 6,500 shooter days occurring on 9,000 acres (3,600 hectares), mostly in June and July, 1998 (Perry, U.S. Forest Service pers. comm. 1998). These projections were derived from local prairie dog density data and numbers of kills reported by shooters. Gross estimates of the number of modern shooters of prairie dogs and their potential take, based on reports from the field, suggest that hundreds of thousands of black-tailed prairie dogs are probably shot across their range annually.
Large, healthy populations appear to be able to withstand considerable removal by shooting and remain viable (Bourland and Dupris, Cheyenne River Sioux Tribe, in litt. 1998, Finnegan et al., Rosebud Sioux Tribe, in litt. 1998). Accordingly, the shooting of hundreds of thousands of individuals across the extensive range of the black-tailed prairie dog where millions of individuals occur, will not likely adversely impact the overall population of a species where each female can produce an average of four young annually. Conversely, small local populations already depressed by disease and other adverse influences may suffer shooting impacts as additive losses. Shooting impacts also may contribute to population fragmentation and preclude or delay recovery of colonies reduced by other factors such as sylvatic plague.
The Service believes that impacts on the species due to recreational shooting are a low threat at present.
3.2.3 Overall Threat of Overutilization for Commercial, Recreational, Scientific or Educational Purposes
Overall, the Service believes that the impact on the species due to commercial interest in the species as a pet is not a threat at present; and that the impact due to recreational shooting is a low threat at present.
3.3 DISEASE OR PREDATION
The Service believes that sylvatic plague is likely the most important factor in recent reductions of many black-tailed prairie dog populations throughout a significant portion of the range of the species. Approximately 66 percent of the species range has been affected by plague (Black-footed Ferret Recovery Foundation in litt. 1999).
Sylvatic plague is a disease caused by the bacterium Yersinia pestis, which fleas acquire from biting infected rodents and other species and then transmit via a bite. The disease also can be transmitted directly between animals. The term "sylvatic" refers to the occurrence of the disease in the wild. It also may be referred to in its bubonic, pneumonic, or septicemic forms, depending on the affected portion of the organism in which it is observed (Berkow 1982). Hereinafter, the use of the term "plague" will be inclusive of all forms of the disease in wild animals.
Cully (1989) summarized plague reports in 76 species of 5 mammalian orders in the United States, although it is primarily a rodent disease. It can seriously affect humans, although it responds well to modern treatment (Center for Disease Control 1997). Rodent species vary in their susceptibility to plague. Some species may act as hosts or carriers of the disease or infected fleas and show little or no symptoms. Conversely, black-tailed and Gunnisons prairie dog populations demonstrate nearly 100 percent mortality when exposed to plague (Barnes 1993, Cully 1993) and cannot be considered carriers.
Plague is an exotic disease foreign to the evolutionary history of North American species (Gage, Center for Disease Control, pers. comm. 1999). Black-tailed prairie dogs show neither effective antibodies nor immunity to the disease. Death occurs quickly in prairie dogs exposed to plague; notable symptoms often do not develop prior to death (Cully 1993). Some rodents may act as enzootic hosts or reservoirs, maintaining the disease at a static level of intensity where plague recurs (focal areas or foci), and acting as carriers (Barnes 1993, Cully 1993). If other rodent species, e.g., prairie dogs, inhabit the same area, the enzootic species may transfer plague to them, causing an outbreak that can spread to nonfocal areas and result in an epizootic. Because epizootic hosts, such as black-tailed prairie dogs, suffer nearly 100 percent mortality, epizootics are often short-lived.
220.127.116.11 Extent of Plague.
Plague was first observed in wild rodents in North America near San Francisco, California, in 1908 (Eskey and Haas 1940). It spread eastward across the continent following its introduction and still appears to be expanding its range, although not as rapidly as in its early years. Human plague cases of wild rodent-flea origin were first documented in California in 1908 (Eskey and Haas 1940), Oregon in 1934, Utah in 1936, Nevada in 1937, Idaho in 1940, New Mexico in 1949, Arizona in 1950, Colorado in 1957, Wyoming in 1978, Washington in 1984, and Montana in 1987 (Barnes 1993). Plague was first observed in Gunnisons prairie dogs in northwestern Arizona in 1932, in eastern Arizona in 1937, and in New Mexico in 1938. It was first recorded in Utah prairie dogs in Utah and white-tailed prairie dogs in Wyoming in 1936 (Eskey and Haas 1940). In 1945, following control efforts in South Park, Colorado, plague epizootics were noted in Gunnisons prairie dogs. By 1949, only 5 percent of the original 915,000 acres (371,000 hectares) of occupied Gunnisons habitat remained. Approximately 67 percent of the acres lost was attributed to plague (Ecke and Johnson 1952).
The first reported incidence of plague in black-tailed prairie dogs noted in published literature occurred in Texas in 1946 (Miles et al. 1952). Plague also was detected in fleas collected from black-tailed prairie dogs in Montana in the 1940s (Gage, Center for Disease Control, pers. comm. 1999). Although no reports of any effects on the species are available from this time period. The lack of such reports may be due to the occurrence of few black-tailed prairie dogs at this time due to intensive control efforts. However, by the mid to late 1990s, black-tailed prairie dog colonies in Montana were reduced by approximately 50 percent from the late 1980s, largely due to plague (Montana Dept. Fish, Wildlife & Parks 1998). Large complexes in south Phillips County, including the Charles M. Russell National Wildlife Refuge, and at Fort Belknap and Northern Cheyenne Reservations were among the areas impacted.
Plague has been in the United States for less than 100 years, allowing very little time for any resistance to evolve in native wildlife. It has been observed in black-tailed prairie dogs for approximately 50 years. The introduction of the disease to this continent around 1900 has contributed to the overall decline of the black-tailed prairie dog (Barnes 1993, Cully 1993). The eastward movement of plague in prairie dog populations underscores the possibility that South Dakota (the last largely plague-free State within the range of the black-tailed prairie dog) may experience outbreaks in the future (Gage, Center for Disease Control, pers. comm. 1999). Although the disease has not been documented in black-tailed prairie dog colonies in South Dakota, the Center for Disease Control (1997) has reported plague in the species in Wyoming and North Dakota counties contiguous with the South Dakota border. Additionally, in 1992, a report of plague titre in coyote (Canis latrans) and badger (Taxidea taxus) blood was reported from Sioux County, Nebraska (adjoining South Dakota) near a black-tailed prairie dog colony (Schenbeck, U.S. Forest Service, pers. comm. 1999a). The prairie dog population in this colony declined to near zero during the summer of 1992, and the cause was believed to be due to plague (Virchow et al. 1992). Additionally, in 1995, a badger, coyote, and red fox (Vulpes vulpes) were collected in southwestern South Dakota with plague titres in their blood, indicating exposure to the disease (Center for Disease Control 1997).
Currently plague is widespread throughout 66 percent of the historic range of the black-tailed prairie dog (except in most of South Dakota and portions of Kansas, Nebraska, North Dakota, and Oklahoma) (see Section 3.6.2) and is carried by many rodent species (Barnes 1982). It is likely no coincidence that four of the largest seven remaining black-tailed prairie dog complexes are in South Dakota. Black-tailed prairie dog complexes throughout much of the species range have been or likely will be challenged by plague repeatedly, especially if it becomes more persistent in the ecosystem. Populations have been reduced more in Arizona and New Mexico near the southwest plague focus identified by Barnes (1982) than in other portions of the species range (Table 1). Plague data from 1971 to1980 reconfirmed the geographic range of plague activity in the United States as described by Eskey and Haas (1940) and extended records of its occurrence in various species from the 101st to as far east as the 97th meridian in Texas (Barnes 1982). It is possible that plague epizootics create a "ripple effect" with major epizootics occurring in the western portion of the black-tailed prairie dog range, smaller epizootics occurring further east, and positive titres detected in some mobile species still further east (Gage, Center for Disease Control, pers. comm. 1999). Gage believes that black-tailed prairie dog populations are subject to plague wherever they are located; he has stated that there may be some areas less vulnerable to infection than others, but that there are no entirely safe areas.
18.104.22.168 Effects of Epizootics on Populations.
Given the communicability and lethality of plague, an epizootic may affect an entire colony in a similar manner as a pathogen may affect an individual animal. An entire black-tailed prairie dog colony may disappear just as an individual black-tailed prairie dog would die from a plague infection. The BFF Recovery Foundation (1999) suggested that, with regard to plague, the vulnerability of black-tailed prairie dog populations can be, in part, evaluated based upon species dispersal distance and the distances between complexes. For example, in Montana, if black-tailed prairie dog colonies within 3 miles (5 kilometers) of each other are grouped into a complex, there are 57 complexes of 100 acres (40 hectares) or larger in size, representing approximately 95 percent of the black-tailed prairie dog occupied habitat in the State. Each of these complexes is vulnerable to significant reductions due to plague. Accordingly, across the range of the species there may be only a few hundred complexes which include most black-tailed prairie dog populations. These large complexes, while resistant to the normal repressive factors affecting small isolated populations, e.g., genetic suppression, stochastic events, etc., are nevertheless, quite vulnerable to plague due to their interconnectedness.
Data from the Rocky Mountain Arsenal National Wildlife Refuge illustrates that plague can significantly depress black-tailed prairie dog populations (Seery and Matiatos, in prep., U.S. Fish and Wildlife Service 1998). The refuge encompassed a 4,800-acre (1,940-hectare) black-tailed prairie dog complex in 1988. Although efforts were made to control plague (e.g., periodic dusting of burrows with the insecticide Permethrin) and no control or other major adverse artificial factors affected the population, several outbreaks have decimated the complex, reducing the amount of occupied habitat by 99 percent on two occasions. Moreover, subsequent population recovery has been only approximately 50 percent of the previous population peak for the two periods of recovery (Seery, U.X. Fish and Wildlife Service, pers. comm. 1998). The number of individuals was reduced to less than 1 percent of their previous numbers on one occasion. Although the periodic translocation of approximately 12,000 prairie dogs from off-site onto the refuge between 1989 and 1998 boosted populations subsequent to plague-induced declines, a trend analysis predicts that even with intensive management and no additional adverse factors, black-tailed prairie dog populations on the Rocky Mountain Arsenal National Wildlife Refuge may be extirpated subsequent to additional anticipated epizootics.
Plague, once established in an area, becomes persistent and periodically erupts, with the potential to extirpate local black-tailed prairie dog populations. After several epizootics, black-tailed prairie dogs at the Rocky Mountain Arsenal National Wildlife Refuge (probably the most studied site for plague on a large population of this species) have neared extirpation. This phenomenon may be occurring at other formerly large black-tailed prairie dog complexes across much of the western portion of the species range, such as at Northern Cheyenne Reservation in southeastern Montana. A plague epizootic on the Reservation started in 1991 and continued through 1996 (Young 1997), removing 97 percent of the black-tailed prairie dog population (Fourstar, Bureau of Indian Affairs, pers. comm. 1998). Subsequently, the population increased from a low of 378 acres (153 hectares) of occupied habitat to 963 acres (390 hectares). However, Young (University of Arizona, pers. comm. 1998) does not believe that this complex will recover to its former status.
Biggins (U.S. Geological Survey, Biological Resources Division, pers. comm. 1998) reports long-term, plague-related declines for white-tailed prairie dogs near Meeteetse, Wyoming, where periodic limited recoveries appear to be less robust than for black-tailed prairie dogs. Although white-tailed prairie dog populations in Shirley Basin, Wyoming, have been significantly reduced by plague, their subsequent recovery has been somewhat more robust than at Meeteetse (Wichers, Wyoming Game and Fish Department, in litt. 1999). The Service believes that plague is likely affecting many prairie dog populations across the western United States in a similar manner. The effects of plague on prairie dogs may be exacerbated in smaller, isolated colonies where populations are not buffered by large numbers (where some individuals may escape infection by chance) and where recovery may be hampered by limited immigration from other colonies.
Plague outbreaks will probably recur where they have previously occurred. Epizootics in prairie dogs may be sporadic and localized in small colonies, but in large interconnected colonies may affect large areas. Small isolated colonies may not recover. If they do recover, it usually requires approximately 4-5 years to regenerate and then they again become receptive to a plague epizootic (Barnes 1982, Barnes 1993). However, this observation is based on the relatively short history of the disease on the continent and the fact that larger colonies are more likely to be noticed than smaller ones. In New Mexico, Cully et al. (1997) observed that population growth rate increased in a colony of Gunnisons prairie dogs following a plague epizootic and anticipated that the population would recover in 6-7 years. However, a second epizootic was experienced 4 years after the first. Consequently, 12 years following the initial epizootic, the population was still a small percentage of its original level.
The Service believes that impacts on the species due to disease (plague) are a moderate threat at present. Plague has significantly reduced several large complexes and has contributed to the extirpation of many small complexes. However, it does not affect all populations simultaneously. Consequently, some recovery may occur, largely via unaffected adjacent populations, before its reoccurrence.
The Service believes that predation is not likely a major factor affecting overall black-tailed prairie dog populations, but it may be important locally or contribute to the effects of other factors. The species is an important prey animal and experiences significant demands on its population. Animals that prey on prairie dogs include the badger, black-footed ferret, bobcat (Lynx rufus), coyote, gray fox (Urocyon cinereoargenteus), grizzly bear (Ursus americanus), long-tailed weasel (Mustela frenata), mountain lion (Felis concolor), red fox, swift fox, bullsnake (Pituophis melanoleucus), rattlesnake (Crotalus sp.), ferruginous hawk, golden eagle (Aquila chrysaetos), prairie falcon (Falco mexicanus), red-tailed hawk (Buteo jamaicensis), several other species of hawks, and humans (Hoogland 1995). Little information is available to quantify the impact of these predators on prairie dogs.
There is no evidence to indicate that predation has an adverse impact on the viability of black-tailed prairie dog populations rangewide. Although it is conceivable that unusual or intense levels of predation could have some effect, it would likely be localized and of short duration, such as during periods of raptor migration. For example, approximately 200 ferruginous hawks were observed in a single day on the Rocky Mountain Arsenal National Wildlife Refuge in 1989, when the black-tailed prairie dog complex on this site was the largest colony along the Front Range of Colorado (Lockhart, U.S. Fish and Wildlife Service, pers. comm. 1998). This situation involved a high density of raptors preying on a small area of black-tailed prairie dog occupied habitat. However, no long-term effects on prey species were observed, despite the fact that black-tailed prairie dogs formed the major component of the prey base for wintering raptors at the Rocky Mountain Arsenal National Wildlife Refuge (Seery and Matiatos in prep.). Cully (1986) reported that raptor densities increased sevenfold during autumn migrations in the Moreno Valley of New Mexico where Gunnisons prairie dogs occurred.
The Service believes that impacts on the species due to predation are not a threat at present.
3.3.3 Overall Threat of Disease or Predation
Overall, the Service believes that impacts on the species due to disease (plague) are a moderate threat at present, but that impacts due to predation are not a threat at present.
3.4 THE INADEQUACY OF EXISTING REGULATORY MECHANISMS
Many States, Tribes, and Federal Agencies recognize the historic decline and ecological significance of the black-tailed prairie dog, but few use available regulatory mechanisms to conserve the species. At least one government entity in most States promotes their reduction. However, some limited regulatory mechanisms exist for conservation of the species. Additionally, State and Federal agencies do not differentiate between black-tailed prairie dogs and other species of prairie dogs occurring within the current range of the black-tailed prairie dog (e.g., Colorado, Montana, New Mexico, and Wyoming). The Service believes that inadequate regulatory mechanisms are a contributing factor affecting overall black-tailed prairie dog populations.
Mulhern and Knowles (1995) reported that all States within the historic range of the black-tailed prairie dog classify the species as a pest for agricultural purposes and either allow or require their eradication. They noted that in Colorado, Kansas, South Dakota, and Wyoming, Statewide or local mandatory controls are in effect; and in Montana, New Mexico, Nebraska, North Dakota, Oklahoma, and Texas, control is not mandatory, but assistance may be provided to landowners. State wildlife agencies in many States classify black-tailed prairie dogs by categories such as "non-game" and permit licensed or unlicensed shooting with no limitations on take or season. A review of the species in seven States within the central and northern Great Plains by Knowles (1995) reported that all of these States except North Dakota have laws that require eradication under various circumstances. Nebraska repealed regulatory directives mandating control of the species in 1995. In the 10 States where the black-tailed prairie dog currently exists, only Colorado currently has restrictions on shooting (Knowles 1998). However, this restriction pertains only to contest hunts. In Arizona, where the species has been extirpated, the hunting season was closed on black-tailed prairie dogs in 1999 (Shroufe, Arizona Game and Fish Department, in litt. 1999).
Arizona--The Arizona Game and Fish Department classifies all prairie dogs native to the State, black-tailed and Gunnisons, as nongame mammals. In 1999, the hunting season for black-tailed prairie dogs was closed (Shroufe, Arizona Game and Fish Department, in litt. 1999). Arizona does not require the eradication of prairie dogs for agricultural purposes or promote recreational shooting of prairie dogs (Shroufe, Arizona Game and Fish Department, in litt. 1998). The black-tailed prairie dog is listed as endangered on the Arizona "Threatened Native Wildlife" list (Arizona Game and Fish Department 1988). This list is being modified into a State list of "Wildlife of Special Concern" and AGFD has proposed the black-tailed prairie dog for inclusion on the new list (Van Pelt, Arizona Game and Fish Department, pers. comm. 1998).
Colorado--The Colorado Division of Wildlife requires a resident or non-resident hunting license for prairie dog shooting unless the animals are on a persons own land. The season is year-round, with no bag or possession limit. However, for hunt contests, no participant may take more than five prairie dogs during the contest. In 1999, the Colorado State Legislature passed a bill prohibiting the translocation of prairie dogs and other species without the consent of the countys commissioners (Van Pelt in prep.). This bill limits prairie dog conservation efforts in the State (Boucher, pers. comm. 1999). A number of environmental groups have asked the CDOW to include the black-tailed prairie dog on their List of Special Concern (Kahn, Colorado Division of Wildlife, in litt. 1998), but this has not occurred. The Petitioner notes that Colorado agriculture control statutes classify prairie dogs as "destructive rodent pests," authorizing counties to destroy them, as an abatement of a public nuisance, without limitations (National Wildlife Federation 1998).
Kansas--The State of Kansas considers black-tailed prairie dogs as agricultural pests and mandates control if an adjoining landowner files a complaint (Knowles 1995). In recent years, some counties have invoked "Home Rule" to take over authority for prairie dog control from the townships and impose mandatory control requirements on landowners. The landowner is given the opportunity to control prairie dogs on his land and if he fails to do so it is done by the county at the landowners expense (Van Pelt in prep.). The Kansas Department of Wildlife and Parks reports that the shooting of prairie dogs in Kansas is not unrestricted since a resident or nonresident hunting license is required and established methods of take are listed (Williams, Kansas Department of Wildlife and Parks, in litt. 1998). The Petitioner notes that Kansas considers the black-tailed prairie dog as both a pest and as wildlife, and recreational shooting of prairie dogs is unrestricted and may occur year-round (National Wildlife Federation 1998).
Montana--The Montana Department of Fish, Wildlife and Parks requires no license to shoot prairie dogs and no limits on take or season exist. The MDFWP protects prairie dogs on two State parks as important features of those parks (Graham, Montana Department of Fish, Wildlife and Parks, in litt. 1998). The MDFWP identifies the black-tailed prairie dog as a State "species of special concern" (Flath 1998). As a partner in black-footed ferret recovery efforts, MDFWP helped to develop "Montana Prairie Dog Guidelines" to monitor and conserve prairie dog ecosystems Statewide. These guidelines include management goals and voluntary restrictions on recreational shooting in southern Phillips County, the location of the largest complex in Montana and part of one of the seven largest colonies throughout the species range. However, the agency has been unsuccessful in its attempts to classify the black-tailed prairie dog as a "nongame species in need of special management." This classification, if implemented, would allow the formulation of management guidelines and regulations. A species conservation plan for the black and white-tailed prairie dogs in Montana also is being developed (Montana Department of Fish, Wildlife, and Parks in prep.).
The Montana Department of Agriculture classifies prairie dogs as "rodents" and "vertebrate pests." The MDA assists landowners in control of prairie dogs if requested, but it is not mandated (Sullins, Montana Department of Agriculture, pers. comm. 1999).
Nebraska--The black-tailed prairie dog is currently considered an unprotected nongame species in Nebraska and can be taken in any manner, without restrictions on shooting or control activities. Permits are not required for residents; nonresidents must have a small-game hunting permit. A statute requiring extermination of prairie dogs on private and State-owned lands was repealed in 1995 (Van Pelt in prep.). The Nebraska Game and Parks Commission recognizes prairie dog shooting as an acceptable recreational activity, but suggests that shooting be avoided at times when prairie dogs have dependent young in the burrows and that shooters take responsible measures to avoid disturbance of other wildlife species that use prairie dog colonies (Amack, Nebraska Game and Parks Commission, in litt. 1998).
New Mexico--The New Mexico Department of Game and Fish requires a license to shoot prairie dogs, but there are no bag limits or restrictions (Knowles 1998). The Petitioner reports that New Mexico considers the prairie dog as a "rodent pest" and mandates that landowners destroy prairie dogs on notice (National Wildlife Federation 1998).
North Dakota--The black-tailed prairie dog is classified as a nongame wildlife species by the North Dakota Game and Fish Department. A resident is not required to purchase a hunting license to shoot prairie dogs, however nonresidents are required to purchase one. There are no bag limits or seasons set for prairie dogs. The State of North Dakota considers the black-tailed prairie dog as a pest. The State Legislative Assembly passed a resolution urging the Service not to list the species (North Dakota Legislative Assembly in litt. 1999). The North Dakota Department of Agriculture and the county weed boards have regulatory authority over control efforts (Van Pelt in prep.). A guidebook is available to aid prairie dog shooters in finding colonies (North Dakota Game and Fish Department undated). The Petitioner states that North Dakota considers black-tailed prairie dogs "gophers" and "pests" and authorizes extermination on private lands (National Wildlife Federation 1998).
Oklahoma--The Oklahoma Department of Wildlife Conservation classifies the black-tailed prairie dog as a Category II Mammal Species of Special Concern. ODWC placed a moratorium on control of prairie dogs in January 1972 and canceled it in February 1973 (Lewis and Hassien 1973). Prairie dog eradication is no longer mandatory in Oklahoma, but is assisted by some State agencies and local governments. Although control and recreational shooting of the species can occur on private land, the ODWC does not promote either activity (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1998). A license for recreational shooting is required by residents and nonresidents. Prairie dogs may be killed by rifle, shotguns, handguns, and bows and arrows. A permit is required from ODWC prior to any control. Prairie dogs cannot be reduced in any county to fewer than 1,000 individuals and control is not permitted on public lands (Van Pelt in prep.).
South Dakota--The South Dakota Game and Fish Department classifies the black-tailed prairie dog as a predator/varmint and requires a resident or nonresident license to shoot prairie dogs in the State; however, there are no seasons or bag limits. The South Dakota Weed and Pest Control Statute designates the species as a Statewide declared pest. Therefore the existence of prairie dogs constitutes an infestation, giving the State authority to enter private land and exterminate the animals. Once a county declares an infestation, landowners are responsible for the costs to control prairie dogs on their land whether they want control or not (Van Pelt in prep.).
Texas--The Texas Parks and Wildlife Department designates the black-tailed prairie dog as a nongame species and is prohibited by State statutes from listing them as a State endangered species. A license is required to hunt prairie dogs, but there is no season or bag limit. In 1999 a new regulation was established which requires a nongame collection or dealers permit to possess more than 10 prairie dogs or to sell any number of prairie dogs (Van Pelt in prep.). This law does not regulate the killing of prairie dogs for recreational, agricultural, or nuisance purposes (Sansom, Texas Parks and Wildlife Department, in litt. 1998). The Texas Health and Safety Code authorizes counties to control prairie dogs and gives the Texas Department of Agriculture responsibility for providing information regarding control to requesting counties (Van Pelt in prep.).
Wyoming--The black-tailed prairie dog is a nongame wildlife species in Wyoming and is listed as a Species of Special Concern by the Wyoming Game and Fish Department. No license is required to hunt prairie dogs, and there is no season, bag limit, or restriction on method of take (Van Pelt in prep.). The WGFD supports development of seasons and bag limits for the black-tailed prairie dog (Wichers, Wyoming Game and Fish Department, in litt. 1998). The Wyoming Department of Agriculture lists the species as a pest. The Wyoming Weed and Pest Control Act of 1973 authorizes counties to enter private property to control prairie dogs if damage has been documented to neighboring landowners (Knowles 1995). The Wyoming State Legislature passed a resolution urging the Service not to list the species (Wyoming State Legislature in litt. 1999).
Mulhern and Knowles (1995) estimated that 30 percent of black-tailed prairie dog colonies occur on tribal lands. Four of the seven remaining large complexes of 10,000 acres or more (Cheyenne River Sioux Tribe, Fort Belknap, Pine Ridge, and Rosebud Sioux Tribe) occur on tribal lands. Two Tribes (Cheyenne River Sioux Tribe in South Dakota and Fort Belknap in Montana) have prairie dog management plans in place (Knowles 1995). The Cheyenne River Sioux Tribe drafted a prairie ecosystem management plan in 1992 that prohibits control on 44,100 acres (17,860 hectares) of black-tailed prairie dog occupied habitat. The Fort Belknap Reservation is an active Black-footed Ferret Reintroduction Area and manages its black-tailed prairie dogs; it has curtailed its former extensive prairie dog shooting program. No extensive control of prairie dogs has occurred on Cheyenne River Sioux Tribe, Fort Belknap, or Rosebud Sioux Tribe (in South Dakota) lands in recent years due to concerns related to the conservation of black-footed ferrets. However, there are active recreational shooting programs on these and other tribal lands. The Oklahoma Department of Wildlife Conservation states that tribal management programs for the species can not be considered more sophisticated or positive "because the money generated from recreational shooting goes to a tribal wildlife program rather than a state or federal wildlife program" (Duffy, Oklahoma Department of Wildlife Conservation, in litt. 1998).
The following Tribes provided specific information regarding management status of the species on their lands:
Cheyenne River Sioux Tribe (in South Dakota).
The Cheyenne River Sioux Tribe does not classify the prairie dog as a pest and does not require or encourage their eradication. The Tribe reported that black-tailed prairie dog seasons are year-round and without limits on Cheyenne River lands. However, shooting is not unregulated because the Tribes Game, Fish, and Parks Program issues all prairie dog hunters a license and stamp. Prairie dog hunters are required to complete harvest report cards that document the amount and locations of harvest. The Tribe indicated that if prairie dog populations decline below management goals, its Game, Fish, and Parks Program will restrict season lengths and/or number of hunting permits (Bourland and Dupris, Cheyenne River Sioux Tribe, in litt. 1998; Dikeman et al., Cheyenne River Sioux Tribe, in litt. 1999).
Crow Creek Sioux Tribe (in South Dakota).
The Crow Creek Sioux Tribe indicated approximately "60 active grounds" exist on the Reservation. Recreational shooting is allowed and "appears to have no effect on their numbers." Chemical control is not allowed and the black-tailed prairie dog is reported as abundant (Miller, Crow Creek Sioux Tribe, in litt. 1998).
Rosebud Sioux Tribe (in South Dakota).
The Rosebud Sioux Tribe Department of Natural Resources established a licensing system for black-tailed prairie dogs in 1989. In 1998, a new license structure was implemented in an attempt to reduce the number of shooters (Finnegan et al., Rosebud Sioux Tribe, in litt. 1998). License sales were reduced by approximately 50 percent from approximately 4,000 licenses in 1997 to 2,000 licenses in 1998 (Finnegan, Rosebud Sioux Tribe, pers. comm. 1999).
Knowles (1995) reviewed Federal regulatory management policies as they relate to the black-tailed prairie dog. Significant black-tailed prairie dog occupied habitat is found on public lands managed by the BIA, BLM, the Service, the Forest Service, and the NPS. The APHIS and the Environmental Protection Agency (EPA) do not manage public lands; however, they impact the species through their regulatory authorities.
Bureau of Indian Affairs.
The BIA has a trust responsibility to oversee management of tribal lands. The BIAs involvement in prairie dog control efforts has been principally through management of funding for prairie dog control programs on tribal lands. The BIA is authorized to make rules and regulations concerning range protection. In the northern Great Plains, from 1978 through 1992, BIA funding was responsible for the control of more prairie dog habitat than any other Federal Agency in the country (Roemer and Forrest 1996). Following control efforts at Pine Ridge Reservation in South Dakota in the early 1980s (described in Section 3.5.2), additional control of large black-tailed prairie dog populations was proposed in the mid-1990s via BIA-sponsored control programs on Fort Belknap, Cheyenne River Sioux Tribe, and Rosebud Sioux Tribe Reservations. These control efforts were halted due to concerns for black-footed ferret reintroduction which precluded Federal funding of these efforts. Limited control still occurs on these Reservations with non-Federal funds.
Bureau of Land Management.
The BLM manages prairie dogs to meet multiple-use resource objectives including production of livestock forage and preventing prairie dogs from spreading to adjacent State or private lands. Although control is no longer actively conducted by the BLM, it still allows control to occur by other agencies on its lands and it still allows significant levels of unregulated sport shooting (Knowles 1995). In a memorandum dated June 23, 1999 and expiring September 30, 2000, the BLM instructed all of its State Directors within the range of the black-tailed prairie dog to "ensure that all actions authorized, funded or carried out by their respective field offices do not contribute to the need to list this species" (Colby, Bureau of Land Management, in litt. 1999). The Western Association of Fish and Wildlife Agencies (Greer, Western Association of Fish and Wildlife Agencies, in litt. 1999) supports this moratorium. The BLM also anticipates implementing a mandatory restriction on prairie dog hunting in portions of south Phillips County, Montana, due to the lack of success of current voluntary closures in the area (64 FR 56213).
Fish and Wildlife Service.
The Service manages over 500 National Wildlife Refuges and their satellites, but only about 15 refuges, satellites, or Waterfowl Production Areas have black-tailed prairie dogs. Only two refuges have any significant amount of occupied habitat. On the Charles M. Russell and UL Bend National Wildlife Refuges in Montana, 5,150 acres (2,090 hectares) of black-tailed prairie dogs are managed. Burrows have been treated with insecticide in an attempt to reduce fleas and disease transmission, and prairie dogs are moved to recolonize vacant or low density towns (Matchett 1997). This area is managed to enhance its value as a black-footed ferret reintroduction site. The Rocky Mountain Arsenal National Wildlife Refuge in Colorado, which manages black-tailed prairie dogs to support and enrich a diversity of wildlife, is attempting to recover its populations subsequent to repeated plague epizootics (U.S. Fish and Wildlife Service 1998).
Shooting of prairie dogs is currently prohibited on all refuges and satellites. Limited control has occurred on a few wildlife refuges, primarily as a measure to prevent their spread onto adjacent private lands. Minimal control around office buildings and campgrounds has been reported on one refuge. Some control has occurred as a "Good Neighbor Policy" on one refuge in South Dakota. During the current status review period for the black-tailed prairie dog, all control efforts regarding the species have been suspended on Service lands (Clark, U.S. Fish and Wildlife Service, in litt. 1999).
U.S. Forest Service.
The Forest Service manages approximately 3,700,000 acres (1,500,000 hectares) of National Grasslands, which support approximately 42,460 acres (17,200 hectares) of black-tailed prairie dog occupied habitat, approximately 1.1 percent of the National Grasslands (Sidle, U.S. Forest Service, in litt. 1999). For example, at Thunder Basin National Grasslands in Wyoming, the 1995 long term management objective (10-15 years) was to retain approximately 4,000 acres (1,600 hectares) of occupied habitat out of 16,500 acres (6,700 hectares) of then existing occupied habitat within 572,000 total acres (232,000 hectares) (U.S. Forest Service 1995b). Presently, the Forest Service estimates that at Thunder Basin approximately 18,000 acres (7,000 hectares) of occupied habitat exist out of 478,000 acres (193,000 hectares) of potential prairie dog habitat (Sidle, U.S. Forest Service, in litt. 1999). Buffalo Gap National Grasslands in South Dakota contains approximately 597,000 acres (242,000 hectares). Approximately 455,000 acres (184,000 hectares) are considered potential prairie dog habitat; and 13,270 acres (5,370 hectares) of occupied habitat currently exist; or 3 percent of potential prairie dog habitat is currently occupied (Sidle, U.S. Forest Service, in litt. 1999).
On other National Grasslands lower management objectives exist. In Kansas, the Cimarron National Grasslands Prairie Dog Management Plan specifies the maintenance of 12-25 black-tailed prairie dog colonies on 500-1,200 acres (200-500 hectares) out of 108,177 acres (43,812 hectares); and in Colorado, the Comanche National Grassland Prairie Dog Management Plan specifies that 30-65 colonies of 2,000-4,000 acres (800-1,600 hectares) be maintained on 418,963 acres (169,680 hectares) (U.S. Forest Service 1995a).
In response to a request from the National Wildlife Federation and the positive 90-day finding, the Forest Service issued a moratorium on control of black-tailed prairie dogs during the current status review period on all lands administered by the Forest Service. The Western Association of Fish and Wildlife Agencies (Greer, Western Association of Fish and Wildlife Agencies, in litt. 1999) supports this moratorium. The Forest Service also noted their intention to manage for larger prairie dog populations via new planning efforts subject to completion and approval (Manning, U.S. Forest Service, in litt. 1999).
National Park Service.
The NPS is involved with prairie dog control programs through integrated pest management guidelines. During 1982-1992, four national parks in the northern Great Plains were involved in prairie dog control, including Badlands National Park, South Dakota, with 5,423 acres (2,196 hectares) controlled; Wind Cave National Park, South Dakota, with 1,922 acres (778 hectares) controlled; Theodore Roosevelt National Park, North Dakota (trace amounts controlled); and Devils Tower National Monument, Wyoming (trace amounts controlled) (Roemer and Forrest 1996). In a memorandum dated January 14, 1999, the NPS instructed Superintendents of National Parks within the Midwest Region where prairie dogs occur (Badlands, Fort Larned, Scotts Bluff, Theodore Roosevelt, and Wind Cave units) to suspend further treatment of prairie dog colonies (with few exceptions) until a final determination is made on their status (Schenk, National Park Service, in litt. 1999). No information was available regarding NPS lands in the southern portion of the black-tailed prairie dogs range.
Animal and Plant Health Inspection Service.
The APHIS-Wildlife Services (APHIS-WS) (formerly Animal Damage Control) influences prairie dog control programs through its involvement in the field, its grant-in-aid program to States, its technical assistance to other State, tribal, and Federal agencies, and private landowners, and its distribution of prairie dog toxicants. For example, APHIS-WS offered its assistance in black-tailed prairie dog control via commercial radio announcements in the Texas panhandle in August, 1999 (Harmon, U.S. Fish and Wildlife Service, pers. comm. 1999). Roemer (1997) reported that during 1990-1994, APHIS-WS was involved in control of 101,660 acres (41,140 hectares) of prairie dogs. They also were involved in programs in the early 1980s at the Pine Ridge Indian Reservation (Oglala Sioux Tribe) in South Dakota that controlled 458,600 acres (185,700 hectares) of black-tailed prairie dogs from 1980 to 1984 (Roemer and Forrest 1996). The APHIS Denver Wildlife Research Center also has directed and conducted research related to the efficiency of prairie dog and other rodent control.
Environmental Protection Agency.
The EPA deals indirectly with prairie dog control through pesticide labeling programs including restrictions to protect wildlife. Presently, labeling does not restrict prairie dog control, but does address concerns for the endangered black-footed ferret.
In Canada, the black-tailed prairie dog is designated as vulnerable by the Committee on the Status of Endangered Wildlife in Canada. Control is prohibited and only private landowners are permitted to shoot prairie dogs (Fargey, Grasslands National Park, pers. comm. 1998).
The black-tailed prairie dog is listed as threatened by the Lista de las Especies Amerzadas, the official threatened and endangered species list of the Mexican Government (SEMARNAP 1994). List et al. (1997) reported that in Mexico, laws exist to stop control, but are often not enforced, and extensive control occurs. There are no protected areas for the black-tailed prairie dog in Mexico (Ceballos et al. 1993).
3.4.6 Overall Threat of Inadequacy of Existing Regulatory Mechanisms
The Service believes that impacts on the species due to inadequate regulatory mechanisms are a moderate threat at present.
3.5 OTHER NATURAL OR MANMADE FACTORS AFFECTING THE SPECIES CONTINUED EXISTENCE
3.5.1 Rodent Control
Control programs conducted in response to concerns related to potential forage competition with domestic livestock have significantly reduced black-tailed prairie dog populations. This species of prairie dog is believed to have been particularly impacted because its tendency toward larger and more densely populated colonies, when compared with other species of prairie dogs, creates more conflicts with landowners (Clark 1973, Fagerstone and Ramey 1996, Roemer and Forrest 1996). The Service believes that control efforts have been an important influence limiting black-tailed prairie dog populations, especially large-scale, well-organized efforts conducted early in the century. Current control efforts are limited compared to historic efforts, but impact a significant portion of black-tailed prairie dog occupied habitat annually.
22.214.171.124 Rodent Control Efforts Prior to 1972.
Control efforts resulted in extirpation of the black-tailed prairie dog in Arizona (Alexander 1932). Similar control efforts in Texas resulted in the persistence of only remnant populations in areas where historically, the largest known populations of the species once occurred (Bureau of Sport Fisheries and Wildlife 1961, Cheatheam 1977, Cottam and Caroline 1965).
A well-documented control effort has occurred over most of the range of the black-tailed prairie dog (Anderson et al. 1986, Bell 1921, Cain et al. 1972, Forrest and Proctor in prep., Hanson 1993, Hubbard and Schmitt 1983, Lantz 1903, Lewis and Hassien 1973, Linder et al. 1972, Merriam 1902, Roemer and Forrest 1996, Shriver 1965). It is important to note that prairie dog control occurred repeatedly in most areas and figures cited for acreage controlled may include retreatment of the same areas in subsequent years. Therefore, annual acreage estimates of lands treated do not always equate to total loss of habitat. However, control (usually in conjunction with other factors) has led to the complete loss of occupied habitat in many areas. Organized prairie dog control gained momentum from 1916 to 1920 when prairie dogs were controlled on tens of millions of acres of western rangeland (Bell 1921). Federal programs were responsible for much of this effort, which was initiated by congressional appropriations to the Bureau of Biological Survey in 1915 (Cain et al. 1972).
From 1937 to 1968, 30,447,355 acres (12,331,178 hectares) of prairie dog occupied habitat were controlled (Cain et al. 1972), less than what was controlled during the much shorter period from 1916 to 1920 described by Bell (1921). Of the lands controlled from 1937 to 1968, 75 percent was treated by 1950, with an average of more than 1.6 million acres (650,000 hectares) treated annually. From 1951 to1968, the average amount of prairie dog occupied habitat controlled annually dropped to approximately 430,000 acres (174,000 hectares) per year. In the 1960s, several States reached their lowest estimates of black-tailed prairie dog occupied habitat (Table 1). According to Cain et al. (1972), in the late 1960s, the public became interested in Federal animal control programs, including prairie dog control, and this interest resulted in increased attention to ecological considerations. Several toxicants previously used for pest or predator control were banned. In 1972, Compound 1080, which was used extensively in prairie dog control efforts, was banned by Presidential Executive Order II 11643 for use on Federal lands, in Federal programs, or on private lands (Barko 1997). Although prairie dog control continued via other toxicants, it was at a reduced rate.
126.96.36.199 Recent Rodent Control Efforts.
The most extensive control efforts in recent years have been conducted in the Northern Great Plains (U.S. Forest Service 1998). Roemer and Forrest (1996) summarized recent Federal and State control efforts on approximately 1,045,524 acres (423,437 hectares) in South Dakota, Montana, and Wyoming. From 1978 to 1992, an average of 69,701 acres (28,229 hectares) were treated annually in these three States. These estimates did not include estimates for private control or control involving indirect State or Federal assistance. Forrest and Proctor (in prep.) estimated that in recent years private land control and control conducted at the local level probably affected "tens of thousands" of acres of black-tailed prairie dog occupied habitat on an annual basis.
The BIA administered the last large-scale control effort for black-tailed prairie dogs on the Pine Ridge Reservation in South Dakota in the early 1980s. This effort resulted in the eradication of most prairie dogs on approximately 458,618 acres (185,740 hectares) from 1980 to 1984. From 1985 to 1986, 240,000 acres (97,000 hectares) were retreated (Roemer and Forrest 1996). In 1987, after these efforts, 57,281 acres (23,199 hectares) remained (Tschetter 1988). Additional control continued. Current estimates of occupied habitat range from 20,000 to 30,000 acres (8,000 to 12,000 hectares) (Yellowhair, Pine Ridge Sioux Tribe, pers. comm. 1999). Following control efforts on Pine Ridge, three additional extensive control efforts targeted for the Cheyenne River Sioux Tribe and Rosebud Sioux Tribe Reservations in South Dakota and Fort Belknap Reservation in Montana were halted due to concerns regarding the lack of available black-footed ferret reintroduction sites.
The amount of control of black-tailed prairie dogs on lands managed by the Forest Service has declined. For example, on Thunder Basin National Grassland, from 1988 to 1992, an average of 3,900 acres (1,600 hectares) was controlled annually; and from 1993 to 1997, an average of 1,190 acres (480 hectares) was controlled annually. As another example, on Buffalo Gap National Grassland, from 1988 to 1992, an average of 3,880 acres (1,570 hectares) was controlled annually; and from 1993 to 1997, an average of 1,750 acres (709 hectares) was controlled annually (Sidle, U.S. Forest Service, in litt. 1999). As noted in Section 3.4.3, the Forest Service has issued a moratorium on control of black-tailed prairie dogs during the current status review period on all Forest Service lands (Manning, U.S. Forest Service, in litt. 1999).
The APHIS-WS is a participant in control of prairie dogs. Forrest and Proctor (in prep.) reported that from 1990 to 1996, APHIS-WS sold, used, or was involved in the distribution of a total of 266,976 gas cartridges, 3,532,499 tablets of aluminum phosphide fumigants, and 169,161 pounds of zinc phosphide-treated bait, primarily for control of prairie dogs. From 1990 to 1994, 101,660 acres (41,170 hectares) were treated by APHIS-WS, with 94 percent of this total on private land. Control efforts at the State and local level on private lands are largely undocumented. The Pocatello Supply Depot sold 244,880 pounds of zinc phosphide bait from 1988 to 1992, enough to control 128,500 acres (52,040 hectares) of prairie dog occupied habitat annually. The APHIS-WS used an average of 24,166 pounds yearly during this same period. Therefore, the authors concluded that approximately half of Pocatellos output is distributed to others. If so, private control may occur on about 60,000 acres per year.
Depending on which figures are used, it appears that 10-20 percent of current black-tailed prairie dog occupied habitat may be controlled annually by Federal, State, local, and private entities. Without the additive adverse effects of other impacts, black-tailed prairie dog populations can recover to an appreciable degree from control efforts in some areas. For example (but perhaps as an exception given the uniqueness of the State as a site free of plague), the acreage occupied by black-tailed prairie dogs in South Dakota was reduced to approximately 60,000 acres (24,000 hectares) in 1968 (Rose 1973), but recovered to approximately 700,000 acres (280,000 hectares) by 1980 (Tschetter 1988), prior to initiation of control efforts at Pine Ridge Reservation. The Service is unaware of any similar level of increase in this or other populations within the past 20 years, although Thunder Basin National Grasslands has experienced similar rates of increase. Following control efforts, South Dakota was estimated to contain 184,000 acres (74,500 hectares) of occupied habitat (Tschetter 1988). Nevertheless, control efforts in some specific areas, balanced between agricultural and wildlife conservation interests, can likely be accommodated, given the resiliency of the black-tailed prairie dog. However, given the disproportionate amount of black-tailed prairie dog occupied habitat on tribal lands, just four control efforts could reduce the total amount of black-tailed prairie dog occupied habitat in the United States by approximately 22 percent. These four Reservations have either had recent large scale control efforts which significantly reduced occupied habitat or have had recent plans for such programs.
In September 1999, the Petitioner requested the Service to readdress this issue based on reports of increased control efforts (Graber, National Wildlife Federation, in litt. 1999). The Service has limited information that indicates some increased efforts have occurred, but has not reached any conclusions at this time.
3.5.2 Synergistic Effects
An important manmade factor affecting many black-tailed prairie dog populations is the likely simultaneous operation of all the factors described previously. The Service believes that many factors (alone, in combination with each other, and synergistically) have influenced and continue to influence black-tailed prairie dog populations. Evaluations of these influences will require more effort than that involved in this finding.
3.5.3 Overall Threat of Other Natural or Manmade Factors Affecting the Species Continued Existence
The Service believes that impacts on the species due to other natural or manmade factors are a moderate threat at present.
3.6 VULNERABILITY OF THE SPECIES IN PERSPECTIVE
3.6.1 Vulnerability of Complexes
Historically, large black-tailed prairie dog populations coped successfully with various depressant factors, except plague, on a different scale; populations were large and robust while threats were few with only temporal effects. Presently, most populations are significantly reduced and must cope with many persistent influences that depress populations, both temporally and permanently. There has been a general long-term rangewide decline as well as some recent areawide declines in black-tailed prairie dog populations. Although some populations where plague was absent increased appreciably 20-30 years ago from historic lows following the restrictions on the use of Compound 1080 in 1972, only a few increases have been observed in isolated locations across the species range over the last 10-15 years. Conversely, several large black-tailed prairie dog complexes have been markedly reduced during this periodsouth Phillips County, Fort Belknap Reservation and Northern Cheyenne Reservation, Montana; Rocky Mountain Arsenal National Wildlife Refuge and Comanche National Grasslands, Colorado; Cimarron County, Oklahoma; and Janos Nuevo Casas Grandes, Mexico (Figure 1).
It might be assumed that the persistence of the black-tailed prairie dog as a species is secure because it is relatively abundant in absolute numbers when compared with many other species with smaller populations that are not thought to be vulnerable. Many wildlife species in North America that have experienced significant population declines remain viable, e.g., various game species such as the pronghorn (Antilocapra americana). However, the black-tailed prairie dog is a highly social species that for the most part responds to major factors causing population reductions (e.g., plague and control) as a colony rather than on an individual basis. Additionally, inadequate regulatory mechanisms are in place for the black-tailed prairie dog as compared to game species. Therefore, populations may not be as viable as their absolute numbers might suggest.
A significant portion of existing black-tailed prairie dog occupied habitat rangewide occurs in a few large complexes. Using current estimates of occupied habitat for the species and information about the size of the seven large remaining prairie dog complexes from the Services black-footed ferret recovery program, it may be determined that 36 percent of the remaining occupied habitat for the species in North America occurs in seven complexes larger than 10,000 acres (4,000 hectares). These complexes includeBuffalo Gap National Grassland, Conata Basin, South Dakota (approximately 15,000 acres/6,000 hectares); Cheyenne River Sioux Tribe Reservation, South Dakota (approximately 45,000 acres/18,000 hectares); Fort Belknap Reservation, Montana (approximately 15,000 acres/6,000 hectares); Janos Nuevo Casas Grandes, Mexico (approximately 90,000 acres/36,000 hectares); Pine Ridge Reservation, South Dakota (approximately 20,000 acres/8,000 hectares); Rosebud Sioux Tribe Reservation, South Dakota (approximately 70,000 acres/28,000 hectares); and Thunder Basin National Grassland, Wyoming (approximately 20,000 acres/8,000 hectares). The potential vulnerability of these complexes to control efforts or plague is notable.
Other than disease and control efforts, larger colonies are likely more resistant to various depressant factors, but smaller colonies may be threatened by factors affecting isolated remnant populations, e.g., stochastic events and inbreeding, in addition to the major factors that continue to suppress most prairie dog colonies, e.g., plague, control, and habitat loss. Smaller colonies may not be relied on for the long-term viability of the species since their continued persistence may be questionable (Clark 1989, Gilpin and Soule 1986, MacArthur and Wilson 1967, Shaffer 1981, Wilcove et al. 1986, Wilcox and Murphy 1985).
There are few black-tailed prairie dog colonies that are large enough to successfully cope with various threats over the long term and these are particularly susceptible to control efforts and plague epizootics. The Service believes that depressant factors (especially plague and control) continue to cause local extirpations that could lead to the species becoming vulnerable in a significant portion of its range without management intervention. Paramount among these factors is the existence of an exotic disease in the species environment. Approximately 66 percent of the black-tailed prairie dog range has been affected by plague (see Section 3.6.2). Bright (1998) reviewed the influences of various exotic species on native flora and fauna; he concluded that plague has crippled surviving prairie dog populations. This disease is a recurring depressant influence on black-tailed prairie dog populations throughout a significant portion of their range. Only in South Dakota and parts of other States in the eastern portion of the species range is it absent at present. If plague establishes itself in these areas (Kansas, Nebraska, North Dakota, South Dakota), it could have an even more significant negative effect on the overall status of the species.
Plague appears to have advanced from the western portion of the black-tailed prairie dog range eastward. This implies that the eastern portions of the species range provide a more secure habitat; however, habitat conversion has occurred throughout the species range, in a generally east to west progression. If unsuitable lands (e.g., urban areas, cultivated lands, forested areas, etc.) and lands impacted by plague are not considered, approximately 10 percent of the black-tailed prairie dogs historic range is suitable habitat, with South Dakota providing the bulk of plague-free suitable habitat (Black-footed Ferret Recovery Foundation in litt. 1999).
Extant populations of black-tailed prairie dogs may or may not be large enough to be resilient to ongoing or future environmental challenges and related potential declines. Quammen (1996) provided examples of species that appeared to be abundant, but suddenly became very rare. For example, he reported that the passenger pigeon (Ectopistes migratorius) numbered in the billions around 1810 and in the low millions by the 1880s, yet was extinct in the wild by 1900. Habitat destruction and over-harvesting depressed passenger pigeon numbers to a few million, a level too low for a highly social and colonial species to function (Halliday 1980). The black-tailed prairie dog numbered in the billions around 1900, exists as a few million at present, and appears to be declining in a significant portion of its range. The advantages of sociality in the past (e.g., breeding, feeding, predator defense) may no longer offset its modern disadvantages (e.g., vulnerability to disease and control).
Although there are an apparent large number of individual black-tailed prairie dogs (even after large historic declines in the amount of occupied habitat), the black-tailed prairie dog, as a colonial species occurring in isolated groups, may be as vulnerable as species on islands when confronted by environmental challenges (MacArthur and Wilson 1967). The vulnerability of species on islands to threats from which they cannot escape is compounded by the limitations on recruitment caused by isolation. This situation may be similar for isolated black-tailed prairie dog colonies impacted by habitat barriers, habitat modification, disease, and other adverse impacts. The species may have difficulty in coping with these challenges without the advantage of its historic abundance and its wide distribution. The appropriate time for successful management intervention to stabilize a colonial species such as the black-tailed prairie dog may be earlier than for some other species.
Accordingly, the vulnerability of the black-tailed prairie dog as a species to population reductions may be related less to its absolute numbers across its range than to the number of colonies in which it exists, their size, their geospatial relationship, existing barriers to immigration and emigration, and ultimately the number and nature of the direct threats to the species, both alone and in concert.
3.6.2 Area Evaluations
The stability of any portion of a species population is specific to its locality and the time at which its viability is evaluated. The Service has identified eight areas within the range of the black-tailed prairie dog which appear to have different sets of circumstances affecting the persistence of local remnant populations of the species (Figure 3). These evaluations, including the respective area estimates for historic range, utilize habitat analysis provided by the BFF Recovery Foundation (1999).
Percentage estimates noted for current occupied habitat in Areas 4, 7, and 8 utilize Service estimates presented in Table 1, column 10. All North Dakota and South Dakota black-tailed prairie dog occupied habitat is assumed to occur in Area 8, and all Nebraska and Kansas black-tailed prairie dog occupied habitat is assumed to occur in Area 7. All black-tailed prairie dog occupied habitat in Oklahoma is assumed to occur in Area 4. These allocations are generally correct.
!Area 1 encompasses that portion of the historic black-tailed prairie dog range in Arizona. This area represents approximately 2 percent of the total historic range. The species is reported to be extirpated in this area, with no remaining black-tailed prairie dog occupied habitat. Extirpation is believed to have been due largely to early control efforts prior to the occurrence of plague in the area. Accordingly, the species (i.e., any proposed reintroductions) may be considered very vulnerable in this area at present.
!Area 2 encompasses that portion of the historic black-tailed prairie dog range in parts of Kansas, Nebraska, Oklahoma, and Texas east of the 98th meridian. This area represents approximately 8 percent of the total historic range. The species is extirpated to nearly extirpated in this area, with little or no remaining black-tailed prairie dog occupied habitat, largely due to extensive changes in land use resulting in habitat loss. Accordingly, the species may be considered very vulnerable in this area at present.
!Area 3 encompasses that portion of the historic black-tailed prairie dog range in parts of New Mexico and Texas, west of the Pecos River. This area represents approximately 12 percent of the total historic range. Only very small remnant populations persist in this area, with very little remaining black-tailed prairie dog occupied habitat, largely due to impacts from control efforts and plague. Accordingly, the species may be considered very vulnerable in this area at present.
!Area 4 encompasses that portion of the historic black-tailed prairie dog range in parts of Colorado, Montana, Nebraska, North Dakota, New Mexico, Oklahoma, Texas, and Wyoming, bounded on the southwest by the Pecos River, on the south, west, and north by the limit of the species range, and on the east by the easternmost records of plague occurrence. This area represents approximately 50 percent of the total historic range and contains approximately 60 percent of the current black-tailed prairie dog occupied habitat in the United States. Populations have been reduced in this area largely due to plague, control efforts, and land use changes resulting in habitat loss. Recent significant population declines due to plague have occurred throughout much of this area (Thunder Basin National Grasslands in Wyoming is the only known relatively large complex in Area 4 not yet impacted by plague). Accordingly, the species may be considered vulnerable in this area at present.
!Area 5 encompasses that portion of the historic black-tailed prairie dog range in Mexico. This area represents approximately 4 percent of the total historic range and contains approximately 12 percent of current black-tailed prairie dog occupied habitat rangewide. Populations have been reduced in this area largely due to land use changes resulting in habitat loss and control efforts. Accordingly, the black-tailed prairie dog may be considered vulnerable in this area at present.
!Area 6 encompasses that portion of the historic black-tailed prairie dog range in parts of Kansas, Nebraska, Oklahoma, and South Dakota, bounded on the east by the 98th meridian, on the north by the limit of the species range, on the west by the 99th meridian, and on the south by Texas. This area represents approximately 8 percent of the total historic range. Remnant, scattered populations occur in this area, with very little black-tailed prairie dog occupied habitat, largely due to extensive changes in land use resulting in habitat loss. Accordingly, the species may be considered vulnerable in this area at present.
!Area 7 encompasses that portion of the historic black-tailed prairie dog range in parts of Kansas, Nebraska, and Oklahoma, bounded on the east by the 99th meridian, on the north by South Dakota, and on the west and south by the easternmost records of plague occurrence. This area represents approximately 9 percent of the total historic range and contains approximately 15 percent of the current black-tailed prairie dog occupied habitat in the United States. Populations in this area are fragmented, largely due to changes in land use resulting in habitat loss and control efforts. Populations are much reduced, but persistent and relatively stable. Accordingly, the species may be considered vulnerable in this area, but not within the foreseeable future unless plague becomes more widespread.
!Area 8 encompasses that portion of the historic black-tailed prairie dog range in parts of North Dakota and South Dakota, bounded on the north by the limits of the species range, on the east by the 99th meridian, on the south by Nebraska, and on the west by the easternmost records of plague occurrence. This area represents approximately 7 percent of the total historic range and contains approximately 25 percent of the current black-tailed prairie dog occupied habitat in the United States. Most populations in this area occur in a few relatively large complexes and appear to be resilient. Accordingly, the species is not considered vulnerable in this area, although its clumped distribution could be problematic if plague occurs in the area or if a relatively few well-organized control programs were initiated (as have occurred as recently as 1984 or have been proposed as recently as 1994).