Black Tailed Prairie Dog (Cynomys ludovicianus)
Status of species: Rare
Distribution: Great Plains from southern Saskatchewan south to the Texas panhandle, and southern New Mexico and Arizona into extreme northern Mexico
General Description: Black-tailed prairie dogs are extremely social ground squirrels that live in colonies subdivided into cooperative family groups called coteries. Black-tails lived in very large “towns” distributed continuously across the low-grass prairies of the Great Plains less than 100 years ago. As a result of mass extermination through poisoning, shooting, and habitat shortage, remaining colonies are fragmented and the species now occupies only 1% of its former range. Often referred to simply as “prairie dogs,” black-tails are the “prototype prairie dog,” because they are the most conspicuous and likely to appear in zoos. Because of their complex social interactions and predator defense systems, they have been studied extensively by scientists.
Colony Structure: Black-tailed prairie dogs live in large aggregations, called colonies. If subdivided by topographical features, these colonies will have discrete subunits, called wards. Within these wards are coteries, which contain several females of close kinship, the young of the year, and one or two non-reproductive males (usually yearlings) that are closely related to the females. Coterie members often sniff each other for identification, or touch mouths in a prairie dog “kiss.” Individuals in the same coterie also groom each other to search for lice and ticks. These interactions help distinguish coterie members and facilitate defense of their area from members of other coteries.
Occasionally, coteries split to form new coteries. In these splitting events, one to three females of close kin split from a pre-existing coterie and defend a subsection of the original territory. These unusual events are the only way in which females move from the coterie of their birth.
Black-tailed prairie dogs are part of a prairie ecosystem that includes large ungulates like American bison. Similar to cattle in both behavior and nutritional requirements, bison co-existed with prairie dogs for hundreds of years prior their collective extermination.
Photo by Theodore G. Manno.
Breeding: Both males and females become sexually mature at one or two years of age. During the breeding season (late February to early March), reproductive males compete through territorial displays and fighting to become the sole male associated with particular coteries of females. Females can breed for about one day a year, and males decipher which day this is through anal sniffing. Females will usually copulate exclusively with the male associated with their coterie, but variation from single male copulation occurs for two reasons. First, cuckoldry sometimes occurs when reproductive males invade foreign clans and copulate with females, causing about 5% of young to be fathered by males that are not associated with their coterie. Second, estrus females avoid mating with any father, son, or brother present in their coterie, and will attract the attention of other males to avoid extreme inbreeding. Mating pairs usually copulate belowground, and males sometimes give a mating call before insemination.
During pregnancy (usually 34 or 35 days), females collect nesting material into a burrow contained within the coterie territory, which becomes their natal area. The young are born underground, and are nursed by their mother for 37 to 51 days. However, once the young emerge, “communal nursing” occurs, whereby juveniles are nursed by all members of the coterie rather than just the mother. This behavior may suggest that mothers cannot easily discriminate between their own and others’ offspring in the coterie. Average litter size is three or four young. Female young stay in the coterie of their birth, and males disperse when they become sexually mature.
Predator Defense and Vocalization: Black-tails play a critically important role in the ecosystem as prey for birds, coyotes, bobcats, badgers, and many other predators of the prairie. Part of their defense system includes scanning for predators and alarm calling. During a predatory attack from the ground or air, black-tails (and other species of prairie dog) run to burrow mounds and give repetitious alarm calls. Amazingly, only half of all individuals in the area of the predator will call, as the others watch in silence. The prairie dogs that call are almost invariably individuals that have either descendant or non-descendant kin within earshot. Thus, black-tailed prairie dogs give alarm calls to warn kin of danger, despite the risk of drawing a predator’s attention to themselves. This suggests that the evolution of coloniality in black-tails may stem from the need to deter predation.
Black-tails also give several other vocalizations, most notably their “jump-yip” calls. Unique to black-tails, these humorous calls given from the top of a burrow mound are so explosive that sometimes the caller falls over backwards. The exact purpose of the “jump-yip” call is yet to be determined, but it may be a signal that “All is clear!” after a predatory attack.
Costs and benefits of social living: Although colony life has benefits for deterring predators, group living has its costs. Hostility heats up during breeding season, as males compete for the right to breed. Fights, chases, runaways, and territorial disputes ensue, and these can result in facial injuries, scars, and, occasionally, death and cannibalism.
Ectoparasitism and disease likely spread readily in large, dense colonies. Bubonic plague from Europe, for example, transmits very easily to colonies — and wipes them out fast.
Within coteries, black-tails live in burrows. Most underground tunnels have multiple entrances aboveground to the same burrow, which means several chances to escape if a predator attacks. Burrows can be up to 30 meters long and five meters deep. Some burrows are nursery burrows and are used for child rearing. Because there are multiple entrances to burrows, mothers will sometimes plug alternate routes to their nursery burrows to defend their offspring. The same burrows in a coterie are usually used across generations. Most burrow entrances also have a conspicuous mound of dirt with a high rim to prevent flooding, provide leverage to scan for predators, and promote underground ventilation.
Infanticide is common while the young are still belowground. Amazingly, females actually kill the juveniles of their kin within the coterie, and 39% of all litters are affected. Males kill as well, but female killing is the most common. Because infanticide is so commonplace, females defend the coterie territory and the burrow containing their juveniles from invaders — even if the invader is from their own coterie. Despite several predictions, the reasons for common infanticide are unknown, and further study is in progress.
Ecological Information: Black-tailed prairie dogs are herbivores. Favorite foods in the summer include wheatgrass, buffalo grass, and rabbitbrush. In the winter, black-tails sometimes eat prickly pear cactus (contrary to popular belief, black-tails do not hibernate, although their activity during the winter is intermittent). Black-tails clip tall plants that grow within the coterie, presumably to create an unobstructed view of predators.
Prairie dogs must “fatten up” to survive the long, harsh winters of the Plains.
Photo by Elaine Miller Bond.
Black-tails are important to the ecology of the Plains because they are prey for American badgers, bobcats, coyotes, snakes, weasels, and the endangered black-footed ferret. Their burrows, when abandoned, make homes for snakes. As many as 140 species are thought to be affected by the role of the black-tailed prairie dog in the ecology of North America.
Despite this role, the diet of black-tails has made them a hated animal among many ranchers. Black-tailed prairie dogs once roamed the West, with one aggregation in Texas known to contain 400 million individuals. After it was erroneously reported that 250 prairie dogs consume as much grass as a cow, mass extermination drove black-tailed prairie dogs to the brink of extinction by the 1970’s. Unfortunately, few people have noted that the diet of American bison and cattle are similar, and bison coexisted with prairie dogs for many years. Black-tails and other prairie dogs actually avoid numerous plants that livestock prefer and vice versa. The presence of prairie dogs also improves the quality of certain plants and soils, and prairie dogs are likely to colonize areas that livestock have already overgrazed. The financial trade-off of exterminating prairie dogs is probably not worth the small amount of rangeland they eat. Therefore, despite some minimal conflict between cattle and prairie dogs, continuing the widespread eradication of black-tails and other prairie dogs is unnecessary. The killing of prairie dogs on national lands that are devoted to the protection of wildlife is perhaps even more troubling.
Management Information: The black-footed ferret, which subsists largely on black-tailed prairie dogs, was thought to be extinct until a population of a few individuals was found outside of Meeteetse, Wyoming. Captive breeding commenced, but black-footed ferrets were sometimes released into areas containing no black-tailed prairie dogs, and therefore had nothing to eat.
Unfortunately, many management decisions that are made to exterminate or “thin-out” colonies are based on the misnomers that (1) black-tailed prairie dogs can be censused by counting burrows, (2) black-tailed prairie dogs are prolific breeders, and (3) black-tailed prairie dog colonies increase in area over time. Scientists have found no viable support for any of these hypotheses.
In February 2000, the United States Fish and Wildlife Service determined that the black-tailed prairie dog was “warranted but precluded” for listing as a threatened or endangered species under the Endangered Species Act and added the species to the candidate list. An intent to sue over failing to list the black-tailed prairie dog was filed by conservation groups afterwards. Despite a great deal of petitioning, the United States Fish and Wildlife Service removed the black-tailed prairie dog from the list of candidate species for endangered status in August 2004.
Shortly thereafter, US agencies generated controversy by endorsing the poisoning of black-tailed prairie dogs in Buffalo Gap National Grasslands, South Dakota. The efforts of the prairie dog coalition to protect black-tails and other species of prairie dog have therefore been hindered greatly. However, this ruling was not surprising, given that there are few laws against shooting or poisoning in the western states. Black-tails have protections on private lands, but three states (Kansas, New Mexico, and North Dakota) require mandatory control and only four states (Colorado, Montana, New Mexico, and South Dakota) have partial closures on poisoning. Therefore, black-tailed prairie dogs are protected in national parks (such as Wind Cave NP, South Dakota), but protection elsewhere (including on other national lands) appears to be quite irregular.
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- Written by Theodore G. Manno (PhD student, Auburn University) and Elaine Miller Bond (http://elainebond.home.comcast.net)