Montana Field Guide

Black-tailed Prairie Dog - Cynomys ludovicianus

The black-tailed prairie dog is the largest of the prairie dog species, weighing 700 to 1500 grams and measuring 28 to 33 centimeters from nose to tail (Burt and Grossenheider 1976, Hoogland and Foltz 1982). The overall color of the back and upper sides of the body and tail is generally dark cinnamon with buff coloring on the underside (Burt and Grossenheider 1976, Anderson 1972, Hall 1981). The distal third of the tail is black or dark brown (Hall 1981). They molt twice per year, prior to summer and prior to winter. The skull is about 60 centimeters long, with 22 teeth (Burt and Grossenheider 1976).

Black-tailed prairie dogs are easily separated from the similar white-tailed prairie dogs by the black color of the distal one-third of the tail tip. The black-tailed prairie dog also lacks the distinctive dark face patches of the white-tailed prairie dog. Black-tailed prairie dogs are also found in more dense colonies than are white-tailed prairie dogs. Features of the skull and teeth can also be used to separate the two species of prairie dogs in Montana (Foreseman 2001).

Prairie dogs may also be confused with a number of ground squirrel (Spermophilus) species, but are distinguished by their much more robust body conformation and relatively short tail and their habit of living in much denser colonies with more developed burrow systems.

Montana Range

Black-tailed prairie dogs are not known to migrate, but young animals, primarily males, disperse from their natal burrows in May or June shortly after emerging from hibernation (Garrett and Franklin 1988). Males also disperse from their breeding territory after 2 years to avoid inbreeding with their two year old daughters (Hoogland 1995). Most dispersers remain in the home colony (Hoogland 1995), but others move up to 6 miles in search of new colonies (Knowles 1984).

Prairie dog colonies are found on flat, open grasslands and shrub/grasslands with low, relatively sparse vegetation. The most frequently occupied habitat in Montana is dominated by western wheatgrass, blue grama and big sagebrush (Montana Fish Wildlife and Parks 2002). Colonies are associated with silty clay loams, sandy clay loams, and loams (Thorp 1949, Bonham and Lerwick 1976, Klatt and Hein 1978, Agnew et al. 1986) and fine to medium textured soils are preferred (Merriam 1902, Thorp 1949, Koford 1958), presumably because burrows and other structures tend to retain their shape and strength better than in coarse, loose soils. Encroachment into sands (e.g., loamy fine sand) occurs if the habitat is needed for colony expansion (Osborn 1942).

Shallow slopes of less than 10% are preferred (Koford 1958, Hillman et al. 1979, Dalsted et al. 1981), presumably in part because such areas drain well and are only slightly prone to flooding. By colonizing areas with low vegetative stature, prairie dogs often select areas with past human (as well as animal) disturbance. In Montana, colonies tended to be associated with areas heavily used by cattle, such as water tanks and long-term supplemental feeding sites (Licht and Sanchez 1993, FaunaWest 1998).

Prairie dogs prefer grasses, focusing their herbivory on leaf bases (Koford 1958, Hansen and Gold 1977, Uresk 1984, Krueger 1986). The proportion of other forage types in the diet varies with season, location on town, and vegetative composition (Koford 1958, Hansen and Gold 1977, Uresk 1984, Krueger 1986, Summers and Linder 1978, Bonham and Lerwick 1976, Fagerstone et al. 1981). A 950-gram prairie dog consumes roughly 2.2 pounds of dry laboratory feed per month, or 26.4 pounds per year (Hansen and Cavender 1973 in Hansen and Gold 1977). In terms of forage consumption, Merriam (1902) and Koford (1958) estimated the number of prairie dogs equivalent to one animal unit (A.U.) to be 256 and 335, respectively. Prairie dogs apparently do not require free water (Merriam 1902, Bintz 1984). Water is obtained from green grass and forb shoots (green grasses contain about 68 to 77% water) (Bintz 1984), and, in winter, from succulents such as Opuntia spp., which are about 80% water (Summers and Linder 1978, Fagerstone et al. 1981).

Disperal is heavily biased toward 1 to 2 year old males (Hoogland 1995). Intercolony dispersers may move up to 5 kilometers (Garrett and Franklin 1988). Dispersal was verified in 2 of 1200 marked animals in South Dakota: 1 moved 1 kilometer, the other 2 kilometers (Hoogland 1995). Other species are important in prairie ecosystem--Burrowing Owls, Mountain Plovers, and black-footed ferrets--and depend on prairie dog towns.

General information on black-tailed prarie dogs is available.

The basic prairie dog family group (the coterie) comprises one adult male (at least 2 years old), three or four adult females, and several yearlings or juveniles (Hoogland and Foltz 1982). Large coteries with two or more males occasionally occur. Females remain in their coterie for life, whereas males usually leave within 12 to 14 months after weaning. The coterie system deteriorates in spring during gestation and lactation (King 1959). An organizational level higher than the coterie is the ward (King 1959), a town subdivision described according to topographic features.

Nonexpanding colonies fluctuate significantly between years under normal conditions (King 1959, Koford 1958, O'Meilia et al. 1982, Powell, unpubl. mans.). Spring counts revealed 252 prairie dogs in one year and 92 four years later (Hoogland et al. 1988). Over a 10-year period, the number of weaned juveniles ranged from 4 to 133. Expanding colonies can grow enormously in a few years, increasing population levels 30 to 295% (Hansen and Gold 1977, Garrett and Franklin 1988, Reading et al. 1989). Human control efforts and plague cause substantial fluctuations in population size (see later sections for detailed discussions). In areas where immigration of new individuals is successful, genetic variability within a population is not decreased by large population reductions (Daley 1992).

Under normal conditions, without catastrophic factors operating (e.g., plague or severe predation), rates of mortality vary substantially from year to year, both within and between cohorts (King 1959, Koford 1958, Hoogland et al. 1988). First year survival averaged 50 to 56% for males and females but ranged from 32 to 79% over a 5-year period (Hoogland et al. 1988). Mortality levels drop greatly after the first year, with males typically living to 3 to 4 years and females to 4 to 5 years. King (1955, in Koford 1958) observed 44% mortality in one population, with 36% mortality in the juvenile cohort followed by 22% mortality in the same cohort the following year.

Sylvatic plague is extremely important where it occurs. Sylvatic (bubonic) plague is an exotic disease that can kill more than 99% of prairie dogs in a colony (Cully 1989). The plague bacteria (Yersinia pestis) is transmitted animal-to-animal by infected fleas or contact with infected blood or tissue. The significance of plague in range-wide prairie dog mortality is unclear, though experts agree that where plague occurs it is extremely important in population dynamics (Cully 1992, Brown 1992). Plague may be introduced into a colony by other species or by dispersing prairie dogs, which bring plague-ridden fleas into a colony. Prairie dogs with plague in their bloodstream are very unlikely to introduce plague because the infected animals die quickly (Cully 1992).

Historically, the major predators on prairie dogs were primarily the black-footed ferret and the badger (Bailey 1905 in Koford 1958, Koford 1958, Stromberg et al. 1983, Cully 1989). Raptors, snakes, coyotes, foxes, and bobcats all prey upon prairie dogs, but usually at low rates (Koford 1958, Cully 1989, Powell unpubl. mans.). Starvation associated with drought and severe winters and interactions between old age and other mortality factors contribute to mortality (Koford 1958).

Colonies expand under force of crowding associated with high survival rates and lack of forage (Koford 1958, Garrett et al. 1982). Off-colony attributes facilitating expansion include high forage availability, forage quality, and deep soils. Inter-colony dispersal typically occurs from colonies that have reached carrying capacity, though emigration from young expanding colonies does occur (Garrett et al. 1982, Garrett and Franklin 1988). Dispersal occurs in the spring amongst healthy yearling males and adult females, which disperse an average 2.4 kilometers (Garrett and Franklin 1988). In Nebraska, Steuter (1992) found that prairie dogs attempting to establish new colonies were often killed by badgers. Little is known of the process of new colony initiation. In mixed prairie, prairie dogs may locate and attempt to colonize spots of disturbed land amidst dense grassland (Steuter 1992).

Average colony size is typically 20 to 60 hectares, though colonies of less than 10 hectares to complexes of several hundred hectares are not uncommon (Bishop and Culbertson 1976, Cheatheam 1977, Clark et al. 1982, Knowles 1986). One C. leucurus colony in Utah covered 958 hectares (Clark et al. 1982). Merriam (1902) reported a Texas black-tailed prairie dog colony covering 25,000 square miles. Average burrow density varies widely, from 9 per hectare to at least 250 per hectare (Bishop and Culbertson 1976, Clark et al. 1982, Reading et al. 1989). Thirty to 100 burrows per hectare is common. The number of burrow entrances per hectare also varies substantially, with 50 to 123 a typical range (King 1959). Density of prairie dogs fluctuates within and between years according to colony demographics, environmental conditions, forage availability, and soil and/or vegetation sites within towns (Koford 1958, Powell in progress). Typical adult densities are about 12 per hectare (Koford 1958, King 1959, Powell in progress). After young are weaned (and can be counted aboveground), densities of all age classes totaled typically range from 5 to 30 prairie dogs per hectare (Koford 1958, Hansen and Gold 1977, Knowles 1982 in Knowles 1986, O'Meilia et al. 1982). In three consecutive years, King (1959) noted densities in July on the same site to change from 22 to 14 to 41 prairie dogs per hectare.

In a study of 18 burrow systems Sheets et al. (1971) found the burrows ranging from 3 to 14 feet deep and 13 to 109 feet long, with tunnel diameter of 4 to 5 inches. Passageway plugs are used to inhibit predators, to compartmentalize and block off waste, or when the burrow system is under remodeling (Smith 1958 in Burns et al. 1989, Sheets et al. 1971, Martin et al. 1984, Burns et al. 1989).

The breeding system is harem-polygynous, with most females copulating with one male and males with several females (Hoogland and Foltz 1982). Females achieve estrous as early as the second week in March in Montana (Knowles 1987). Females are in estrous for several hours of only one day per year (Hoogland and Foltz 1982). Gestation averages 35 days (Hoogland 1985, Knowles 1987). Though almost all adult females achieve estrous and many become pregnant, juvenile mortality is high with only one half of copulating females weaning a litter (Hoogland and Foltz 1982). Minimum breeding age is usually two years for both sexes (Hoogland 1985, Knowles 1987). Litter size typically averages about 4 (Knowles 1987) (3 in yearlings, 5 in older females) (Koford 1958).

Vegetation condition does not necessarily affect litter size, with adults producing an average litter size of 4.3 on "fair" rangeland and 5.7 on "severely depleted" rangeland (Koford 1958), but relatively large and small litters may follow high and low rainfall, respectively. Individual females produce one litter per year. Pups stay underground until weaned (Hoogland 1985). Pups appear above ground in about 5 to 8 weeks (mid-May to early June in Montana). Due to forage availability and stress associated with crowding, the number of weaned juveniles increases as the number of adults and yearlings decreases, and vice-versa (Hoogland et al. 1988).

Prairie dogs in Montana are currently a species in need of management and as such, shooting of prairie dogs on public lands (excluding state school trust lands) is regulated. Consult Montana Fish, Wildlife and Parks for the latest regulations. Prairie dogs are managed under the Conservation Plan for Black-tailed and White-tailed Prairie Dogs in Montana (Montana Prairie Dog Working Group 2002). Please consult this plan for details concerning prairie dog management in Montana.