| Black-tailed prairie dog | |
|---|---|
| At Wichita Mountains Wildlife Refuge | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Sciuridae |
| Genus: | Cynomys |
| Species: | C. ludovicianus |
| Binomial name | |
| Cynomys ludovicianus (Ord, 1815) |
|
The black-tailed prairie dog (Cynomys ludovicianus), is a rodent of the family Sciuridae found in the Great Plains of North America from about the USA-Canada border to the USA-Mexico border. Unlike some other prairie dogs, these animals do not truly hibernate. The black-tailed prairie dog can be seen aboveground in midwinter. There is a report of a black-tailed prairie dog town in Texas that covered 64,000 km2 (25,000 sq mi) and included 400,000,000 individuals. Prior to habitat destruction, this species was probably the most abundant prairie dog in central North America. This species was one of two described by the Lewis and Clark Expedition in the journals and diaries of their expedition.
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Black-tailed prairie dogs are generally tan in color, with a lighter colored belly. Their tail has a black tip on it, which is where their name is derived from. Adults can weigh from 1.5 to 3 lb (0.68 to 1.4 kg), males are typically heavier than females. Body length is normally from 14 to 17 in (36 to 43 cm), with a 3 to 4 in (7.6 to 10 cm) tail.
The historic range of the black-tailed prairie dog was from southern Saskatchewan to Chihuahua, Mexico,[2] and included portions of Montana, North Dakota, South Dakota, Wyoming, Colorado, Nebraska, Kansas, Oklahoma, Texas, Arizona, and New Mexico.[3] As of 2007, black-tailed prairie dogs occur across most of their historic range, excluding Arizona;[4][5] however, occupied acreage and populations are well below historic levels.[6]
Black-tailed prairie dogs are diurnal.[4][7][8] Aboveground activity is reduced when rain or snow is falling and during days when the temperature exceeds 100 °F (38 °C).[7][8] They do not hibernate but may become dormant for short periods.[7][8][9]
Black-tailed prairie dogs are native to grassland habitats in North America. They inhabit shortgrass prairie,[5][10][11] mixed-grass prairie,[5][12][13][14][15][16] sagebrush steppe,[10][17] and desert grassland.[2][18]
Habitat preferences for the black-tailed prairie dog are influenced by vegetative cover type, slope, soil type, and amount of rainfall.[19] Black-tailed prairie dog foraging and burrowing activities influence environmental heterogeneity, hydrology, nutrient cycling, biodiversity, landscape architecture, and plant succession in grassland habitat.[7][8][13][15][20][21]
Black-tailed prairie dogs inhabit grasslands including short- and mixed-grass prairie, sagebrush steppe, and desert grasslands. Shortgrass prairies dominated by buffalo grass (Buchloe dactyloides), blue grama (Bouteloua gracilis), and western wheatgrass (Pascopyron smithii),[7][8][12][22] and mixed-grass prairies [5][12][13][14][15][16] that have been grazed by native and nonnative herbivores are preferred habitat.[8][17] Slopes of 2% to 5% and vegetation heights between 3 and 5 inches (7–13 cm) are optimal for detecting predators and facilitating communication.[7][8][12]
In the Great Plains region, black-tailed prairie dog colonies commonly occur near rivers and creeks.[8] 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.[23] The slopes of playa lakes in the Texas panhandle and surrounding regions are used as habitat for the black-tailed prairie dog.[24] Black-tailed prairie dog colonies in Phillips County, Montana, were often associated with reservoirs, cattle salting grounds, and other areas affected by humans.[19]
Black-tailed prairie dogs tolerate "high degrees" of disturbance over long periods of time. 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.[25] 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.[26] 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 Agency, Montana. Roads and cattle trails were found in 150 of 154 black-tailed prairie dog colonies, and colonies were located significantly closer to livestock water developments and homestead sites than randomly located points.[17]
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.[8] Black-tailed prairie dogs do not select specific types of soil to dig burrows,[7] but silty loam clay soils are best for tunnel construction.[8] 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. 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°.[8]
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.[8]
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).[8]
Population density and growth are influenced by habitat quality [7] and are restricted by topographic barriers, soil structure, tall vegetation, and social conditions.[7][8] Urbanization and other types of human development may restrict colony size and spatial distribution. Most plains habitats support at least 13 black-tailed prairie dogs/ha.[8]
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.[7] 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 [4][7] Tunnel depth of black-tailed prairie dogs in central Oklahoma was typically 4 to 5 feet (50–60 inches) deep.[27] Most black-tailed prairie dog colonies contain 20 to 57 burrows/acre.[7][8]
There are three 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.[4][7][8] 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.[14] Rimmed crater mounds may be used as wallowing sites for American bison. Burrow entrances without structures around them are usually located on slopes >10°.[7] The density of black-tailed prairie dog burrow openings depends on both substrate and duration of occupation of an area.[8]
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.[7][8][12] 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.[7][8][18][22] Black-tailed prairie dogs were rarely seen feeding >16 feet (5 m) from colony edges in Wind Cave National Park.[15]
Black-tailed prairie dogs are selective opportunists, preferring certain phenological stages or types of vegetation according to their needs.[7][12][28] When forage is stressed by grazing, drought, or herbicides, black-tailed prairie dogs change their diet quickly. Grasses are preferred over forbs.[8][22] Diet may consist of ≥75% grasses, especially during summer.[22][28] Western wheatgrass, buffalo grass, blue grama [7][8][28] and sedges (Carex spp.) are preferred during spring and summer. Scarlet globemallow (Sphaeralcea coccinea) [7][13][22][28] and Russian-thistle (Salsola kali) [29] are preferred during late summer and fall, but are sought out during every season.[8][13][22] During winter, plains prickly pear (Opuntia polyacantha), Russian thistle, and underground roots are preferred.[7][28] Shrubs such as rabbitbrush (Chrysothamnus spp.), winterfat (Krascheninnikovia lanata), saltbush (Atriplex spp.), and sagebrush (Artemisia spp.) are also commonly eaten.[29] Water, which is generally not available on the short-grass prairie, is obtained from vegetation such as plains prickly pear.[28] Koford [8] estimated that 1 black-tailed prairie dog eats approximately 7 lbs (3 kg) of herbage per month during summer.[29] Cutworms,[29] grasshoppers,[8] and old or fresh American bison scat are occasionally eaten.[4] For a detailed list of foods eaten by black-tailed prairie dogs by month, and ratings of those foods' forage value to cattle and sheep, see.[29] For a complete list of vegetation preferred by the black-tailed prairie dog, see.[30]
Black-tailed prairie dogs live in colonies. Colony size may range from five to thousands of individuals. Colonies are subdivided into two or more wards, based on topographic features, such as hills. Wards are usually subdivided into two or more coteries, which are composed of aggregates of highly territorial, harem-polygynous social groups.[7][8] Individuals within coteries are amicable with each other and hostile towards non-coterie individuals. At the beginning of the breeding season, a coterie is typically composed of one adult male, three to four adult females, and several yearlings and juveniles of both sexes. After the breeding season and prior to dispersal of juveniles, coterie size increases.[7]
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. Males typically leave the natal territory 12 to 14 months after weaning, during May and June,[31] but dispersal may occur throughout the year. 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.[31] Roads and trails may facilitate black-tailed prairie dog dispersal.[8]
Constantine Slobodchikoff and others assert that prairie dogs use a sophisticated system of vocal communication to describe specific predators.[32] According to them, prairie dog calls contain specific information as to what the predator is, how big it is and how fast it is approaching.[32] These have been described as a form of grammar. According to Slobodchikoff, these calls, with their individuality in response to a specific predator imply that prairie dogs have highly developed cognitive abilities.[32] He also writes that prairie dogs have calls for things that are not predators to them. This is cited as evidence that the animals have a very descriptive language and have calls for any potential threat.[32]
There is debate over whether the alarm calling of prairie dogs is selfish or altruistic. It is possible that prairie dogs alarm others to the presence of a predator so they can protect themselves. However it is also possible that the calls are meant to cause confusion and panic in the groups and cause the others to be more conspicuous to the predator than the caller. Studies of black-tailed prairie dogs suggest that alarm calling is a form of kin selection as a prairie dog’s call alerts both offspring as well as non-descended kin like cousins, nephews and nieces.[33] Prairie dogs with kin close by called more often than those that didn’t have kin nearby. In addition, the caller may be trying to make itself more noticeable to the predator.[33] However, it seems that a predator has difficulty determining which prairie dog is making the call due to its "ventriloquial" nature.[33] Also, it seems when a prairie dog makes a call, the others do not run into the burrows but stand on the mounds to see where the predator is, making themselves visible to the predator.[33]
Perhap the most pretentious of prairie dog communication is the territoral call or "jump-yip" display. A prairie dog will stretch the length of its body vertically and throw it's forefeet into the air while making a call. A jump-yip from one prairie dog causes others nearby to do the same.[34]
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.[15]
Minimum breeding age for the black-tailed prairie dog is usually 2 years,[4][7][8] but yearlings may breed if space and food are abundant.[7][8] In Wind Cave National Park, South Dakota, 40% (213 individuals) of yearling females copulated and 9% successfully weaned a litter.[9]
The mating season occurs from late February through April, but varies with latitude and site location of a black-tailed prairie dog colony.[7][8] Estrus occurs for only 1 day during the breeding season.[9]
In Wind Cave National Park, the mean percentage of adult females that weaned a litter each year was 47% ± 14%.[31] 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.[15]
Black-tailed prairie dog gestation is 34 days.[4][7] Parturition occurs underground. Information about litter size at time of birth is unavailable. Mean litter size observed aboveground ranges from 3.0 to 4.9 young/litter.[7][8][9][31] Only 1 litter is produced each year.[9][31]
In captivity, black-tailed prairie dog pups open their eyes at 30 days old.[7] Pups are altricial and remain below ground for up to 7 weeks to nurse.[7][8][9] Maturity is complete at 15 months old.[7] 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.[7] According to Hoogland and others,[31] lifespan is about 5 years for males and 7 years for females.
Major mortality factors include predation, disease, infanticide, habitat loss, poisoning, trapping, and shooting.[4][9][10][31] 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.[9] Infanticide partially or totally eliminated 39% (361 individuals) of all litters. Lactating females were the most common killers.[9] Mortality of young was highest due to heavy predation during the winter and early spring following birth.[7] Mortality increases with dispersal from a colony or coterie.[8]
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.[4][10] Black-tailed prairie dogs are also susceptible to diseases transmitted by introduced animals.[35]
The most common predators of black-tailed prairie dogs are coyotes (Canis latrans),[4][7][15][36] American badgers (Taxidea taxus),[4][8][15][36] bobcats (Lynx rufus),[4][7][36] golden eagles (Aquila chrysaetos),[4][7][8][36] ferruginous hawks (Buteo regalis),[4][36] red-tailed hawks (Buteo jamaicensis),[7] and prairie rattlesnakes (Crotalus viridis).[7][8][36] Although now very rare, black-footed ferrets (Mustela nigripes) were once a major predator of the black-tailed prairie dog.[36]
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.[2][37] For details on their effects on vegetation and soils, see Site-scale characteristics. Research suggests that black-tailed prairie dogs are a keystone species[2][9][37] in some, but not all, geographic areas.[2] 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.[2][27][37][38] Grasslands inhabited by black-tailed prairie dogs support higher biodiversity than grasslands not occupied by black-tailed prairie dogs. See Ceballos and others [37] for a simplified diagram of black-tailed prairie dog activities and impacts in grassland ecosystem function and biological diversity.
Hundreds of species of vertebrates [5][39] and invertebrates[27] are associated with black-tailed prairie dog colonies. Vertebrate species richness on black-tailed prairie dog colonies increases with colony size and density.[19] 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. Rare and declining species such as the black-footed ferret,[5][36][39] swift fox (Vulpes velox), mountain plover (Charadrius montanus),[19] and burrowing owl (Athene cunicularia)[4] are associated with black-tailed prairie dog colonies.[5] Because black-tailed prairie dog foraging activities keep plant development in a suppressed vegetative state with higher nutritional qualities,[18][39] herbivores including red deer (Cervus elaphus), American bison, pronghorn (Antilocapra americana), and domestic cattle often prefer foraging in black-tailed prairie dog colonies.[4][7][8][13][17][20][22][38][39] 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.[16] For a list of vertebrate species associated with black-tailed prairie dog colonies, see.[40]
Biodiversity in shortgrass prairies may be at risk due to the reductions in distribution and occurrence of black-tailed prairie dog. Threats to black-tailed prairie dogs include fragmentation and loss of habitat, unregulated eradication or control efforts, and sylvatic plague.[5][6] 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.[5] Fragmented black-tailed prairie dog colonies are more susceptible to extirpation, primarily by sylvatic plague. 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.[10][17] Roads, streams, and lakes may serve as barriers to sylvatic plague in black-tailed prairie dog colonies.[10]
Black-tailed prairie dogs are frequently exterminated from ranchland, being viewed as a pest. Their habitat has been fragmented, and their numbers have been greatly reduced. Additionally, black-tailed prairie dogs are remarkably susceptible to plague.[41] In 2006, 8 of 8 appearances of plague in black-tailed prairie dog colonies resulted in total colony extinction. Studies in 1961 estimated only 364,000 acres (1,470 km2) of occupied black-tailed prairie dog habitat in the United States. A second study in 2000 showed 676,000 acres (2,740 km2). However, a comprehensive study between 10 states and various tribes in 2004 estimated 1,842,000 acres (7,450 km2) in the United States, plus an additional 51,589 acres (208.77 km2) in Mexico and Canada. Based on the 2004 studies, the US Fish and Wildlife Service removed the black-tailed prairie dog from the Endangered Species Act Candidate Species List in August 2004.[42]
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;[8][13][22][38] however, effects of black-tailed prairie dogs on rangelands are not uniform.[16][20] 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 among colonized and non-colonized sites in either year, nor did the amount of bare ground. 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, “prairie dogs do not substantially alter the essential character of shortgrass vegetation”.[21] 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.[11]
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.[20][38] Conversely, on shortgrass prairie in Colorado, cattle and black-tailed prairie dogs had a 64% similarity in annual diet.[22]
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.[13][39] Grazing by black-tailed prairie dogs may also improve the nutritional qualities of some plants.[18][39] 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.[13] 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. Foraging by black-tailed prairie dogs does not significantly affect steer weights.[22][38] While forage availability and utilization by cattle decreased in black-tailed prairie dog foraging areas, there was no significant 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.[38]
Black-tailed prairie dogs were the most common prairie dog species collected in the wild for sale as exotic pets, until this trade was banned in 2003 by the United States federal government. Prairie dogs in captivity at the time of the ban are allowed to be possessed under a grandfather clause, but no more may be caught, traded, or sold, and transport is only permitted to and from a veterinarian under proper quarantine procedures. The ban was officially lifted on September 8, 2008.[43]
This article incorporates public domain material from the United States Department of Agriculture document "Cynomys ludovicianus".