Subterranean burrows created by black-tailed prairie dogs serve as refuges from the external environment and are one of the most important features of black-tailed prairie dog colonies. They are used for breeding, rearing young, and hiding from predators. Burrows are maintained from generation to generation and serve as stabilizers on the physical and social aspects of the colony [75]. Black-tailed prairie dog nests are located underground in burrows and are composed of fine, dried grass. Nest material is collected throughout the year by both sexes and all age classes [69,75]. Tunnel depth of black-tailed prairie dogs in central Oklahoma was typically 4 to 5 feet (50-60 inches) deep [144]. Most black-tailed prairie dog colonies contain 20 to 57 burrows/acre [20,75,81].
There are 3 types of burrow entrances- dome mounds, rimmed crater mounds, and entrances without structures around them. Entrance features may prevent flooding and/or aid in ventilation [69,75,81]. Dome mounds consist of loosely packed subterranean soil spread widely around the entrance of the burrow and tend to be vegetated by prostrate forbs. Rimmed crater mounds are cone-shaped mounds constructed of humus, litter, uprooted vegetation, and mineral soil. Black-tailed prairie dogs compact the soil of these mounds with their noses, creating poor sites for seedling establishment [23]. Rimmed crater mounds may be used as wallowing sites for American bison. Burrow entrances without structures around them are usually located on slopes >10% [75]. The density of black-tailed prairie dog burrow openings depends on both substrate and duration of occupation of an area [81].
Vegetation heights between 3 and 5 inches (7-13 cm) and a slope of 2% to 5% are optimal for detecting predators and facilitating communication amon black-tailed prairie dogs [25,27,37,75,81]. Grazing cattle keep vegetation short in the vicinity of black-tailed prairie dog colonies, reducing susceptibility to black-tailed prairie dog predators and potentially expanding colony size [59,75,81,89]. Black-tailed prairie dogs were rarely seen feeding >16 feet (5 m) from colony edges in Wind Cave National Park [50].
As of 2007, little information is available on HABITAT RELATED FIRE EFFECTS for the black-tailed prairie dog. Despite the lack of information, some generalizations may be possible based on their habitat requirements. Black-tailed prairie dogs inhabit grasslands including short-grass [26,53,70,77,91,99] and mixed-grass prairie [12,23,25,28,36,45,50,71,99], sagebrush steppe [26,79,104,105], and desert grassland [35,38,89] (see Plant Communities). The effects of fire on grasslands vary with plant community, season, weather patterns, and fire characteristics [74,83,137,149]. Information on black-tailed prairie dog ecology in sagebrush steppe and desert grasslands is sparse. The following information is from short- and mixed-grass prairie habitat. For more information on fire regime characteristics of other potential black-tailed prairie dog habitat, see the table below.
The nutrient content of grassland plants in various grassland habitat types around the world is typically higher following fire [34], and herbivores such as deer (Odocoileus spp.) seek postburn areas [138]. Black-tailed prairie dogs may also seek postburn areas for foraging. Due to the prairie dog's reliance on grass for food, low- to medium-severity fires may be beneficial, while high-severity fire may have negative impacts on the black-tailed prairie dog in the short-term.
Prairie: Blue grama, buffalo grass, and western wheatgrass are dominant grasses in shortgrass prairie and are favorite foods of black-tailed prairie dogs (see Food habits) [44,75,81,130]. Fire generally favors blue grama [2,5,41,125], and either favors or has no long-term effect on buffalo grass [143,147] and western wheatgrass [40,42,51,52]. The effects of fire on these 3 grass species vary depending on the phenological stage, season of burning, fire severity, and/or postfire weather conditions [142,148]. For more information about the effects of fire on the 3 grass species favored by black-tailed prairie dogs, see the FEIS reviews for blue grama, buffalo grass, western wheatgrass.
Blue grama [2,5,41,125], buffalo grass [143,147], and western wheatgrass [40,42,51,52] are generally favored by spring burning, which increases their frequency, biomass, and cover [40,42,62,72,76,100,142]. Spring (April) prescribed burning in mixed-grass prairie in Badlands National Park, South Dakota, favored buffalo grass. Buffalo grass began vegetative expansion and produced seed during the first growing season after fire [142]. Gartner and White [51] report that late spring and early summer burns can cause increases or decreases in western wheatgrass during the 1st growing season, but no difference between preburn and control was evident by the 2nd growing season in mixed-grass prairie communities. In the 1st and 2nd growing seasons following a spring burn in Nebraska mixed-grass prairie, blue grama experienced a significant increase (p<0.10) in basal cover on burned plots compared to unburned plots [119]. On sites in South Dakota, blue grama increased from 4% to 11% cover in the 1st growing season following a spring prescribed burn and increased from 12% to 18% cover during the 2nd growing season [41]. Following early spring prescribed burning in Texas, blue grama yield increased up to 400 lbs/acre (452 kg/ha) in the 1st growing season [147].
According to a 1980 review, during years of normal or higher than normal precipitation, timing of vegetational regrowth is quicker [60,135,147]. During dry years, grasses on the shortgrass prairie are harmed by fire [148]. In a buffalo grass-blue grama community in Hays, Kansas, it took vegetation 3 growing seasons to recover following a spring wildfire when the soil was drier than normal [86].
Fire may favor black-tailed prairie dog colony expansion if it removes woody shrubs and other visual obstructions. Prescribed burning during spring followed by mechanical brush removal in Theodore Roosevelt National Park, South Dakota, resulted in colony expansion into treated areas. Three active black-tailed prairie dog colony sites were chosen for the study: Peaceful Valley, 23.1 acres (9.34 ha); Mike Auney, 65.0 acres (26.3 ha); and Johnson's Plateau, 86.7 acres (35.1 ha). Adjacent to each active colony was a 4.9 acre (2.0 ha) treatment unit and a 4.9 acre control unit. The plant community was not described but was probably either shortgrass or mixed-grass prairie. The treatment units were burned in May 2002. The burns were patchy and incomplete, so mechanical brush removal was used to compensate for the incomplete burning. Over a 1.5 year period, black-tailed prairie dogs expanded their colonies into treated plots significantly (P<0.001) more than control plots. In the 3 treatment plots, there was an average of 335 new burrows and a mean 50.3% expansion in area, compared to 69 new burrows and a mean 1.6% expansion in control plots [98]:
Number of new black-tailed prairie dog burrows and area of colony expansion in treatment and control plots [98]
September 2002 (4 mo postfire) September 2003 (16 mo postfire) Burning and mechanical brush removal Control Burning and mechanical brush removal Control New black-tailed prairie dog burrows Peaceful Valley 192 (419)ª 40 (141) 458 (685) 41 (142) Mike Auney 315 (528) 86 (135) 358 (434) 116 (165) Johnson's Plateau 138 (304) 54 (110) 191 (357) 50 (106) mean (± 1 SE) all colonies 215 ± 52.4 60 ± 13.6 335 ± 77.9 69 ± 23.6 Area of expansion (ha) Peaceful Valley 0.89 0 1.56 -0.05 Mike Auney 1.26 0 1.09 0.10 Johnson's Plateau 0.62 0 0.31 -0.05 mean (± 1 SE) all colonies 0.92 ± 0.19 0 0.99 ± 0.36 0.001 ± 0.047 ª Numbers in parentheses are total number of burrows, including burrows present in the active black-tailed prairie dog colony encompassed by plot margins before experimental manipulations in 2002.Moderate amounts of disturbance appeared to increase plant species diversity in a mixed-grass prairie in Comanche County, Oklahoma. Plant species diversity and richness were compared in 7 treatments containing combinations of large scale, low-severity prescribed fires, light grazing by cattle, severe grazing by black-tailed prairie dogs, and wallowing by American bison. Treatments were not replicated, so significance of differences between treatments was not assessed. The 2 sites with the highest plant species diversity and richness were those with combinations of low- to moderate- severity disturbances (see table below). Plant diversity and richness was lowest on undisturbed study sites, sites that were burned frequently, and severely disturbed sites containing black-tailed prairie dogs [28]:
Plant diversity and richness in 7 undisturbed and disturbed mixed-grassland sites [28]
Treatment
Undisturbed area Lightly grazed by cattle Lightly grazed by cattle, American bison wallows Frequent, low-severity prescribed fire Low-severity prescribed fire, lightly grazed by cattle Low-severity prescribed fire, lightly grazed by cattle, American bison wallows Severe grazing by black-tailed prairie dogs DiversityThe following table provides fire regime information on vegetation communities in which black-tailed prairie dogs may occur, based on the habitat characteristics and species composition of communities black-tailed prairie dogs are known to occupy. There is not conclusive evidence that black-tailed prairie dogs occur in all the habitat types listed, and some community types, especially those used rarely, may have been omitted. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Objectives of ecologists and conservationists often conflict with those of ranchers and rural landowners regarding management of black-tailed prairie dogs [126]. Because black-tailed prairie dogs have a strong positive influence on plant and animal diversity in their native habitat, ecologists and conservationists are concerned regarding declines in their populations over the last century (e.g., [88,111]). Conversely, because black-tailed prairie dogs alter plant community structure and composition [12,29,30,71,81], they have often been regarded as competitors with livestock [18] and are subject to eradication and control efforts.
Ecological role and threats: Black-tailed prairie dogs have been called "ecosystem engineers" due to their influence on the biotic and abiotic characteristics of their habitat, landscape architecture, and ecosystem structure and function [21,35,139]. For details on their effects on vegetation and soils, see Site-scale characteristics. Research suggests that black-tailed prairie dogs are a keystone species [21,35,66,95,97] in some, but not all, geographic areas [35,101,102]. Black-tailed prairie dogs enhance the diversity of vegetation, vertebrates, and invertebrates through their foraging and burrowing activities and by their presence as prey items [21,35,103,141,144]. Grasslands inhabited by black-tailed prairie dogs support higher biodiversity than grasslands not occupied by black-tailed prairie dogs [32,95]. See Ceballos and others [21] for a simplified diagram of black-tailed prairie dog activities and impacts in grassland ecosystem function and biological diversity.
Hundreds of species of vertebrates [99,120] and invertebrates [82,124,144] are associated with black-tailed prairie dog colonies. Vertebrate species richness on black-tailed prairie dog colonies increases with colony size and density [111]. West of the Missouri River in Montana, 40% (100 species) of all vertebrate fauna in prairie habitats rely on black-tailed prairie dog colonies for food, nesting, and/or denning [48]. Rare and declining species such as the black-footed ferret [24,43,47,55,63,99,120,128], swift fox (Vulpes velox), mountain plover (Charadrius montanus) [111], and burrowing owl (Athene cunicularia) [15,69,91,93,104,106,107,131,132] are associated with black-tailed prairie dog colonies [95,99]. Because black-tailed prairie dog foraging activities keep plant development in a suppressed vegetative state with higher nutritional qualities [89,120], herbivores including elk (Cervus elaphus), American bison (Bos bison), pronghorn (Antilocarpa americana), and domestic cattle often prefer foraging in black-tailed prairie dog colonies [12,29,30,59,69,75,79,81,103,120]. Animals that depend on herbaceous cover in sagebrush habitat, such as mule deer (Odocoileus hemionus) and sage grouse (Centrocercus spp.), may be deterred by the decreased vegetative cover on black-tailed prairie dog colonies [71]. For a list of vertebrate species associated with black-tailed prairie dog colonies, see Campbell and Clark [16].
Biodiversity in shortgrass prairies may be at risk due to the reductions in distribution and occurrence of black-tailed prairie dog [82]. Threats to black-tailed prairie dogs include fragmentation and loss of habitat, unregulated eradication or control efforts, and sylvatic plague [90,99]. As a result of habitat fragmentation and prairie dog eradication programs, black-tailed prairie dog colonies are now smaller and more fragmented than in presettlement times. Agriculture, livestock use, and other development have reduced black-tailed prairie dog habitat to 2% of its former range [99]. Fragmented black-tailed prairie dog colonies are more susceptible to extirpation, primarily by sylvatic plague [95]. The effect of roads on black-tailed prairie dogs is debatable. Roads may either facilitate or hinder black-tailed prairie dog movement, depending on the landscape setting. Roads may be easy routes for dispersal, but those with heavy automobile use may increase black-tailed prairie dog mortality [26,79]. Roads, streams, and lakes may serve as barriers to sylvatic plague in black-tailed prairie dog colonies [26].
According to Reading and Beissinger [111] and Lomolino and Smith [88], a primary management goal of black-tailed prairie dog ecosystems should be the maintenance of biodiversity. Maintaining a network of native prairie reserves located in large clusters as well as large, isolated colonies across the black-tailed prairie dog's historic range is recommended [88,111]. Mulhern and Knowles [99] recommend that 1% to 3% of suitable grasslands should be occupied by black-tailed prairie dogs, and 5% to 10% of federally-owned lands should be occupied by black-tailed prairie dogs. In 1990, Miller and others [96] suggested an integrated management plan that satisfies cattle ranching needs and the conservation of grasslands. They proposed that federal money allocated to the black-tailed prairie dog poisoning program be converted into a rebate for ranchers that manage livestock and preserve black-tailed prairie dog colonies [96]. In 1970, Linder and others [87] recommended preserving black-tailed prairie dog colonies for black-footed ferrets by obtaining easements. Ranchers could continue grazing cattle in a normal manner, but an easement would stipulate that black-tailed prairie dogs could not be eliminated or controlled using methods that are detrimental to ferrets. The rancher could be compensated for an increase in the size of black-tailed prairie dog colonies [87].
A habitat suitability index model for black-tailed prairie dog was created by Clippinger [25] to produce indices for year-round habitat requirements for the black-tailed prairie dog. Possible uses of the model include the evaluation of current colony sites for habitat suitability, the evaluation of possibilities for black-tailed prairie dog colony expansion, and the suitability of sites of transplantation or rehabilitation of black-tailed prairie dog. Four habitat variables are considered: percent herbaceous cover, percent slope, height of vegetation, and soil composition. According to the model, any area of short-grass or mixed-grass prairie >6.2 acres (0.25 ha) is suitable habitat for black-tailed prairie dog. Optimal features include silty clay loam soil, ≥15% herbaceous cover with vegetation 3 to 5 inches (7-13 cm) tall, and ≤10% slope [25].
Interactions with domestic livestock: While black-tailed prairie dogs are often regarded as competitors with livestock for available forage, evidence of impacts on rangelands are mixed. Some research suggests that black-tailed prairie dogs have either neutral or beneficial effects on rangeland used by livestock [12,59,81,103]; however, effects of black-tailed prairie dogs on rangelands are not uniform [29,30,71]. In Cimarron National Grassland in southwest Kansas and adjacent private lands in Baca County, Colorado, some vegetational differences were detected between areas colonized by black-tailed prairie dogs and non-colonized areas, although not all differences were consistent among sample years. Species richness and diversity indices did not differ (P>0.05) among colonized and non-colonized sites in either year, nor did the amount of bare ground (P>0.05). The authors conclude that while prairie dogs alter shortgrass prairie such that the vegetation of colonies tends to be distinct from adjacent non-colonized areas, Âprairie dogs do not substantially alter the essential character of shortgrass vegetation [146]. Cattle neither significantly preferred nor avoided black-tailed prairie dog colonies in a study in the shortgrass steppe of northeastern Colorado. Cattle used black-tailed prairie dog colonies in proportion to the colony's availability, and grazed as intensively on colonies as on areas not occupied by black-tailed prairie dog [53].
Competitive interactions between black-tailed prairie dogs and domestic livestock for preferred forage species are unclear. Several studies suggest that black-tailed prairie dogs avoid eating many plants that livestock prefer, and prefer many plants that livestock avoid [29,30,103,136]. Conversely, on shortgrass prairie in Colorado, cattle and black-tailed prairie dogs had a 64% similarity in annual diet [59].
Some changes in plant composition brought about by black-tailed prairie dogs may benefit livestock by encouraging an increase in plants that are more tolerant of grazing, such as needleleaf sedge (Carex duriuscula), sixweeks grass (Vulpia octoflora), and scarlet globemallow [12,89,120]. Grazing by black-tailed prairie dogs may also improve the nutritional qualities of some plants [89,120]. On a shortgrass prairie near Fort Collins, Colorado, plant species diversity was greater inside black-tailed prairie dog colonies than outside of colonies, and perennial grasses such as buffalo grass and forbs increased [12]. While black-tailed prairie dog colonies at Wind Cave National Park typically had lower levels of plant biomass and were dominated by forbs, plants growing on prairie dog colonies had higher leaf nitrogen concentrations than plants in mixed-grass prairie outside colonies [39]. Foraging by black-tailed prairie dogs does not significantly (P>0.05) affect steer weights [59,103]. While forage availability and utilization by cattle decreased in black-tailed prairie dog foraging areas, there was no significant (P>0.05) reduction of steer weight in either of 2 years of study at the USDA's Southern Great Plains Experimental Range near Woodward, Oklahoma. Nutrient cycling, increased soil fertility, and subsequent changes in forage quality partly compensated for reduced forage availability [103].
Relocation: Black-tailed prairie dogs may need to be relocated for re-establishment into areas where they were extirpated, or to ensure no net loss of prairie dog habitat due to development or agriculture. Factors to consider when relocating black-tailed prairie dogs include: soil, slope, elevation, vegetation type, previous use of a site by black-tailed prairie dog, proximity to other black-tailed prairie dog colonies and adjacent landowners, and natural dispersal barriers. See Roe and Roe [116] for details. After relocation, black-tailed prairie dogs may be retained by 1) ensuring that relocation habitat is suitable, 2) use of underground nest chambers modeled after natural nest chambers, 3) acclimating black-tailed prairie dogs to release sites in large retention pens, and 4) providing supplemental food and water as necessary [117]. Survival of captive prairie dogs upon release into the wild may be enhanced by predator training at a young age [123]. In a study conducted by Shier and Owings [123], predators were presented to captive juvenile black-tailed prairie dogs in conjunction with playbacks of black-tailed prairie dog alarm vocalizations. These techniques had an immediate and lasting effect on black-tailed prairie dogs and enhanced predator avoidance once they were released [123].
Control: It is easier to discourage black-tailed prairie dogs before they inhabit an area than to try to eliminate them after they have established a colony [81]. A minimum of 77% elimination of black-tailed prairie dogs must be achieved the first year. If the remaining 23% of the population is not removed, a complete repopulation may occur within 3 years [31]. A cost-benefit analysis revealed that black-tailed prairie dog poisoning costs more than any grazing benefits accrued [95,96]. Additionally, animals such as American badgers, foxes (Vulpes spp.), coyotes, bobcats, weasels (Mustela spp.), golden eagles, and hawks (Buteo spp.) are potential indirect targets of poisoning programs [81]. Shooting black-tailed prairie dogs for population control and recreation is common across their range [69,90,99]. Shooting may decrease the health of black-tailed prairie dog colonies, fragment populations, cause the loss of non-target species, and delay recovery of colonies affected by sylvatic plague [90].
Visual barriers may be an effective, non-lethal method of black-tailed prairie dog control in mixed-grass prairies. By placing a visual obstruction at 1 side of a colony, expansion of the colony in that direction is limited due to the obstruction of the panoramic view. Physical barriers such as steep slopes and tall vegetation with grass stems about 1.5 inches (3.8 cm) apart and >1 foot (12 inches) tall are an effective barrier against black-tailed prairie dog colony expansion [81]. Koford [81] suggests changing a cattle grazing practice to alter the range vegetation and minimize the quick reoccurrence of black-tailed prairie dog damage. To establish a different plant community unsuitable to black-tailed prairie dogs, complete rest for the range or reseeding is suggested. Specialized predators of black-tailed prairie dogs could also be encouraged. For example, poles may be installed in black-tailed prairie dog colonies to encourage predatory raptors to inhabit the area [81].
Habitat preferences for the black-tailed prairie dog are influenced by vegetative cover type, slope, soil type, and amount of rainfall [111]. Black-tailed prairie dog foraging and burrowing activities influence environmental heterogeneity, hydrology, nutrient cycling, biodiversity, landscape architecture, and plant succession in grassland habitat [12,22,29,30,48,50,75,81,139,141,146].
Landscape-scale habitat characteristics: Black-tailed prairie dogs inhabit grasslands including short- and mixed-grass prairie, sagebrush steppe, and desert grasslands (see Plant Communities). Shortgrass prairies dominated by buffalo grass (Buchloe dactyloides), blue grama (Bouteloua gracilis), and western wheatgrass (Pascopyron smithii) [25,37,59,75,81], and mixed-grass prairies [12,23,25,28,36,45,50,71,99] that have been grazed by native and nonnative herbivores are preferred habitat [79,81]. Slopes of 2% to 5% and vegetation heights between 3 and 5 inches (7-13 cm) are optimal for detecting predators and facilitating communication [25,27,37,75,81].
In the Great Plains region, black-tailed prairie dog colonies commonly occur near rivers and creeks [81]. Of 86 black-tailed prairie dog colonies located in Mellette County, South Dakota, 30 were located on benches or terraces adjacent to a creek or floodplain, 30 occurred in rolling hills with a slope >5%, 20 were in flat areas, and 6 were in badland areas [64]. The slopes of playa lakes in the Texas panhandle and surrounding regions are used as habitat for the black-tailed prairie dog [108,109,110]. Black-tailed prairie dog colonies in Phillips County, Montana, were often associated with reservoirs, cattle salting grounds, and other areas affected by humans [111].
Black-tailed prairie dogs tolerate "high degrees" of disturbance over long periods of time [27,52]. New colonies are rarely created on rangeland that is in "good" to "excellent" condition; however, land that is continually heavily grazed for decades reduces habitat quality due to soil erosion [115]. Black-tailed prairie dogs may colonize heavily grazed sites but do not necessarily specialize in colonizing overgrazed areas. Overgrazing may occur subsequent to black-tailed prairie dog colonization [127]. Black-tailed prairie dogs were associated with areas intensively grazed by livestock and/or areas where topsoil had been disturbed by human activities in sagebrush-grassland habitat on the Charles M. Russell National Wildlife Refuge and Fort Belknap Indian Reservation in northeastern Montana. Roads and cattle trails were found in 150 of 154 black-tailed prairie dog colonies, and colonies were located significantly (P<0.001) closer to livestock water developments and homestead sites than randomly located points [79].
Site-scale habitat characteristics:
Vegetation: Plant community structure and species composition are impacted by black-tailed prairie dog colonization, and are related to the age of the colony and the level of expansion taking place [29,30,128]. Vegetation on black-tailed prairie dog colonies is typically of lower stature [50,75,81,146], and characterized by a higher percentage of bare ground, a higher cover of forbs and/or dwarf shrubs, and lower cover of grasses and larger woody plants than surrounding grassland [7,81,139]. As the black-tailed prairie dog colony ages, forbs and dwarf shrubs may dominate; younger colonies are dominated by grasses [29,141]. Black-tailed prairie dog colonies in Wind Cave National Park consisted of 3 vegetational zones. The interior zone was dominated by forbs, the edge zone was dominated by shortgrasses such as blue grama and buffalo grass, and the outer zone consisted of undisturbed mixed-grass prairie dominated by western wheatgrass, grama (Bouteloua spp.), and needlegrass (Stipa spp.) [50].
Shifts in vegetational structure and composition seem to occur about 10 or more years following initial colonization [23,29]. In a mixed-grass prairie in Badlands National Park, South Dakota, a buffalo grass-dominated community remained relatively unchanged 4 to 7 years after a colony was established. When cover of shortgrass (primarily buffalo grass) fell below 75%, about 11 to 13 years after colonization, abrupt vegetational changes occurred. Forbs, armed and/or sprawling grasses, aromatic dicots, and bare ground dominated the area [23]. In Wind Cave National Park, changes in relative cover of graminoids, forbs, and dwarf shrubs occurred sometime between 8 and 26 years following black-tailed prairie dog colonization, while a decrease in litter and an increase in bare ground were detectable 1 to 2 years after colonization, as shown in following table [29]:
Ground cover (%) composition before (0 years) and during 26 years of black-tailed prairie dog colonization [29]
Age (years)
0
1 to 2
3 to 8
>26
graminoids 26 26 25 1 forbs and dwarf shrubs 10 7 11 29 total vegetation 36 33 36 30 litter 48 37 39 11 bare ground 16 30 25 59According to Cid and others [22], the rate of vegetation change after the removal of grazing animals such as black-tailed prairie dogs is influenced by many factors, including grassland type, plant species composition, weather conditions, and prior intensity and duration of grazing [22]. Removal of black-tailed prairie dogs from a landscape by natural or anthropogenic factors could either release suppressed populations of woody plants or provide new habitat for woody plant colonization [4]. The removal of prairie dogs from northern mixed-grass prairies in Badlands National Park, South Dakota, did not result in rapid reestablishment of native vegetation. When seed banks were collected from black-tailed prairie dog colonies, few dominant species typical of mixed-grass prairie germinated in the laboratory compared to seed banks collected off of black-tailed prairie dog colonies. The authors suggested that unless the seed bank is restored, rapid reestablishment of representative mixed-grass prairie would be difficult [45]. In northeastern Colorado, vegetation changes following eradication of black-tailed prairie dogs were relatively minor and did not significantly (P-value not given) improve shortgrass prairie for use by cattle within 5 years. The following table shows vegetation composition on 1 active and 3 abandoned black-tailed prairie dog colonies in a shortgrass prairie. Plant species in the table were listed only if they had >0.5% cover [77]:
Vegetation cover (%) on active and inactive black-tailed prairie dog colonies [77]
Vegetation Active colony 1 year abandoned 2 years abandoned 5 years abandoned western wheatgrass 2.3 5.1 6.9 6.7 ring muhly (Muhlenbergia torreyi) 5.5 0.2 9.0 0.7 Indian ricegrass (Achnatherum hymenoides) ---- ---- ---- 0.6 purple threeawn 2.8 0.4 0.2 0.3 blue grama 20.7 22.8 9.8 22.2 buffalo grass 37.2 32.4 31.9 25.0 perennial grasses (subtotal) 68.5 60.8 57.7 55.2 annual grasses (2 species) ---- 0.1 ---- 0.5 forbs (14 species) 0.1 2.2 0.6 0.4 shrubs/half-shrubs (6 species) 2.1 2.7 1.9 2.0Total vegetation cover (27 species)
70.7 65.5 60.3 58.3Other habitat characteristics: Black-tailed prairie dog distribution is not limited by soil type, but by indirect effects of soil texture on moisture and vegetation. Black-tailed prairie dog colonies occur in many types of soil including deep, alluvial soils with medium to fine textures, and occasionally gravel. Soil that is not prone to collapsing or flooding is preferred [81]. Black-tailed prairie dogs do not select specific types of soil to dig burrows [75], but silty loam clay soils are best for tunnel construction [81]. Surface soil textures in black-tailed prairie dog colonies near Fort Collins, Colorado, varied from sandy loam to sandy clay loam in the top 6 inches (15 cm), with a sandy clay loam subsoil [11]. In northern latitudes, black-tailed prairie dog colonies commonly occur on south aspects due to the dominance of grasses over shrubs and increased solar radiation during winter. Burrows usually occur on slopes <10% [81].
Black-tailed prairie dogs mix the soil horizons by raising soil from deeper layers to the surface. This may significantly affect the texture and composition of soil at different layers. Feces, urine, and carcasses of black-tailed prairie dogs also affect soil characteristics [81].
Home range and population density: The home range and territorial boundaries of black-tailed prairie dogs are determined by the area occupied by an individual coterie. Coteries typically occupy about 1.0 acre (0.4 ha) [81].
Population density and growth are influenced by habitat quality [75,111] and are restricted by topographic barriers, soil structure, tall vegetation, and social conditions [75,81]. Urbanization and other types of human development may restrict colony size and spatial distribution [70]. Most plains habitats support at least 13 black-tailed prairie dogs/ha [81]. In a mixed-grass prairie at Wind Cave National Park, black-tailed prairie dog population densities were as follows [75]:
Black-tailed prairie dog density from 1948 to 1950 [75] Sample date Area of black-tailed prairie dog ward (acres (ha)) PopulationAverage
5.6 (2.3) 50 8.8The currently accepted scientific name for the black-tailed prairie dog is Cynomys ludovicianus
(Ord) [6,54,56,145].
Although not typically distinguished, 2 subspecies were described by Hall
[54]:
Cynomys ludovicianus arizonensis Mearns
Cynomys ludovicianus ludovicianus (Ord) [54]
Age of first reproduction, pregnancy rate, litter size, juvenile growth rate, and first-year survivorship of the black-tailed prairie dog vary depending on food availability [50].
Mating: Minimum breeding age for the black-tailed prairie dog is usually 2 years [69,75,81], but yearlings may breed if space and food are abundant [75,81]. In Wind Cave National Park, South Dakota, 40% (n=213) of yearling females copulated and 9% successfully weaned a litter [66].
The mating season occurs from late February through April, but varies with latitude and site location of a black-tailed prairie dog colony [75,81]. Estrus occurs for only 1 day during the breeding season [66].
Reproductive success: In Wind Cave National Park, the mean percentage of adult females that weaned a litter each year was 47% ± 14% SD (range 30% to 73% over 10 years) [67]. Reproductive success and survival may be greater in young black-tailed prairie dog colonies that have space for expansion. In a young colony (@5 years) with space for expansion in Wind Cave National Park, 88% females were pregnant and 81% of young weaned, compared to an old colony (@30 years) with no room for expansion, where 90% of females were pregnant and 41% of young were weaned [50].
Gestation period and litter size: Black-tailed prairie dog gestation is 34 days [69,75]. Parturition occurs underground. Information about litter size at time of birth is unavailable [65]. Mean litter size observed aboveground ranges from 3.0 to 4.9 young/litter [66,67,75,81]. Only 1 litter is produced each year [66,67].
Development: In captivity, black-tailed prairie dog pups open their eyes at 30 days old [75]. Pups are altricial and remain below ground for @7 weeks to nurse [66,75,81]. Maturity is complete at 15 months old [75]. Lifespan of the black-tailed prairie dog in the wild is unknown, but males >3 years old experience high mortality. Females may live longer than males [75]. According to Hoogland and others [67], lifespan is about 5 years for males and 7 years for females.
Social organization: Black-tailed prairie dogs live in colonies. Colony size may range from 5 to thousands of individuals. Colonies are subdivided into 2 or more wards, based on topographic features, such as hills. Wards are usually subdivided into 2 or more coteries, which are composed of aggregates of highly territorial, harem-polygynous social groups [75,81]. Individuals within coteries are amicable with each other and hostile towards non-coterie individuals [49,75]. At the beginning of the breeding season, a coterie is typically composed of 1 adult male, 3 to 4 adult females, and several yearlings and juveniles of both sexes [31,75]. After the breeding season and prior to dispersal of juveniles, coterie size increases [31,75].
Habits: Black-tailed prairie dogs are diurnal [69,75,81]. Aboveground activity is reduced when rain or snow is falling and during days when the temperature exceeds 100 °F (38° C) [75,81]. They do not hibernate [61] but may become dormant for short periods [66,75,81].
Dispersal: Reasons for dispersal include new vegetative growth at colony peripheries, shortage of unrelated females in a coterie, harassment of females by juveniles, and probably an innate genetic mechanism responding to increased density within a colony [49]. Males typically leave the natal territory 12 to 14 months after weaning, during May and June [67], but dispersal may occur throughout the year [49]. Females generally remain in their natal coterie territories for their lifetime. Intercolony dispersers moved an average distance of 1.5 miles (2.4 km) from their natal site [67]. Roads and trails may facilitate black-tailed prairie dog dispersal [81].
Mortality: Major mortality factors include predation (see Predators), disease, infanticide, habitat loss, poisoning, trapping, and shooting [26,66,67,69,69]. Survivorship for the first year was 54% for females and <50% for males in Wind Cave National Park. Primary causes of death were predation and infanticide [66]. Infanticide partially or totally eliminated 39% (n=361) of all litters. Lactating females were the most common killers [66]. Mortality of young was highest due to heavy predation during the winter and early spring following birth [75]. Mortality increases with dispersal from a colony or coterie [81].
Sylvatic plague, caused by the bacterium Yersinia pestis, can quickly eliminate entire black-tailed prairie dog colonies. Once infected, death occurs within a few days [26,69]. Black-tailed prairie dogs are also susceptible to diseases transmitted by "introduced animals" (species not identified) [13,14].
Human-caused mortality of black-tailed prairie dogs is discussed in Management considerations.
Fire may have negative or positive effects on black-tailed prairie dog habitat depending on burn severity and season. Low-severity burns conducted during spring in non-drought years may stimulate the growth of black-tailed prairie dog colonies by reducing vegetational height and density at the colony periphery [40,42,62,68,72,76,78,98,100,113,133,142]. High-severity burns have the potential of altering the plant community in a black-tailed prairie dog colony, reducing its quality of habitat, at least in the short-term [128]. During the plant growing season, the absence of fire provides optimal conditions for black-tailed prairie dog colony growth [78].
Prescribed burning and mechanical brush removal around the perimeter of black-tailed prairie dog colonies may encourage their expansion. Fire exclusion may be an effective, nonlethal management tool for reducing the expansion of black-tailed prairie dog colonies [98].
