The black-footed ferret (Mustela nigripes), also known as the American polecatHeptner, V. G. (Vladimir Georgievich); Nasimovich, A. A; Bannikov, Andrei Grigorovich; Hoffmann, Robert S. (2001). Mammals of the Soviet Union Volume: v. 2, pt. 1b. Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation. or prairie dog hunter, is a mustelid species native to central North America. It is roughly the size of a mink and is similar in appearance to the European polecat and the Asian steppe polecat. It is largely nocturnal and solitary, except when breeding or raising litters. Up to 90% of its diet is composed of prairie dogs.
The black-footed ferret declined throughout the 20th century, primarily as a result of decreases in prairie dog populations and sylvatic plague. It was declared extinct in 1979, but a residual wild population was discovered in 1981 in Meeteetse, Wyoming. A captive-breeding program launched by the United States Fish and Wildlife Service resulted in its reintroduction into eight western US states, Canada, and Mexico from 1991 to 2009. , over 200 mature individuals are in the wild across 18 populations, with four self-sustaining populations in South Dakota, Arizona, and Wyoming. It was first listed as "endangered" in 1982, then as "extinct in the wild" in 1996 before being moved back up to "endangered" in the IUCN Red List in 2008. In February 2021, the first successful clone of a black-footed ferret, a female named Elizabeth Ann, was introduced to the public.
Evolution Like its close relative, the Asian steppe polecat (with which it was once thought to be conspecific), the black-footed ferret represents a more progressive form than the European polecat in the direction of carnivory. The black-footed ferret's most likely ancestor was Mustela stromeri (from which the European and steppe polecats are also derived), which originated in Europe during the Middle Pleistocene. Molecular evidence indicates that the steppe polecat and black-footed ferret diverged from M. stromeri between 500,000 and 2,000,000 years ago, perhaps in Beringia. The species appeared in the Great Basin and the Rockies by 750,000 years ago. The oldest recorded fossil find originates from Cathedral Cave, White Pine County, Nevada, and dates back 750,000 to 950,000 years ago. Prairie dog fossils have been found in six sites that yield ferrets, thus indicating that the association between the two species is an old one. Anecdotal observations and 42% of examined fossil records indicated that any substantial colony of medium- to large-sized colonial ground squirrels, such as Richardson's ground squirrels, may provide a sufficient prey base and a source of burrows for black-footed ferrets. This suggests that the black-footed ferret and prairie dogs did not historically have an obligate predator–prey relationship. The species has likely always been rare, and the modern black-footed ferret represents a relict population. A reported occurrence of the species is from a late Illinoian deposit in Clay County, Nebraska, and it is further recorded from Sangamonian deposits in Nebraska and Medicine Hat, Alberta. Fossils have also been found in Alaska dating from the Pleistocene.
Description
The black-footed ferret has a long, slender body with black outlines on its paws, ears, parts of its face and its tail. The forehead is arched and broad, and the muzzle is short. It has few whiskers, and its ears are triangular, short, erect and broad at the base. The neck is long and the legs short and stout. The toes are armed with sharp, very slightly arched claws. The feet on both surfaces are covered in hair, even to the soles, thus concealing the claws. It combines several physical features common in both members of the subgenus Gale (least and short-tailed weasels) and Putorius (European and steppe polecats). Its skull resembles that of polecats in its size, massiveness and the development of its ridges and depressions, though it is distinguished by the extreme degree of constriction behind the orbits where the width of the cranium is much less than that of the muzzle.
Although similar in size to polecats, its attenuate body, long neck, very short legs, slim tail, large orbicular ears and close-set pelage is much closer in conformation to weasels and stoats. The dentition of the black-footed ferret closely resembles that of the European and steppe polecat, though the back lower molar is vestigial, with a hemispherical crown which is too small and weak to develop the little cusps which are more apparent in polecats. It differs from the European polecat by the greater contrast between its dark limbs and pale body and the shorter length of its black tail-tip. In contrast, differences from the steppe polecat of Asia are slight, to the point where the two species were once thought to be conspecific. The only noticeable differences between the black-footed ferret and the steppe polecat are the former's much shorter and coarser fur, larger ears, and longer post molar extension of the palate.
Males measure in body length and in tail length, thus constituting 22–25% of its body length. Females are typically 10% smaller than males. It weighs .Biggins, Dean E. and Max H. Schroeder. (1988). Historical and present status of the black-footed ferret. pp. 9397. In Eighth Great Plains Wildlife Damage Control Workshop, USDA Forest Service Gen. Tech. Rpt. RM-154, Rapid City, South Dakota. Captive-bred ferrets used for the reintroduction projects were found to be smaller than their wild counterparts, though these animals rapidly attained historical body sizes once released.
The base color is pale yellowish or buffy above and below. The top of the head and sometimes the neck is clouded by dark-tipped hairs. The face is crossed by a broad band of sooty black, which includes the eyes. The feet, lower parts of the legs, the tip of the tail and the preputial region are sooty-black. The area midway between the front and back legs is marked by a large patch of dark umber-brown, which fades into the buffy surrounding parts. A small spot occurs over each eye, with a narrow band behind the black mask. The sides of the head and the ears are dirty-white in color.
Behavior and ecology
Territorial behavior
The black-footed ferret is solitary, except when breeding or raising litters. It is nocturnal and primarily hunts for sleeping prairie dogs in their burrows. It is most active above ground from dusk to midnight and 4 am to mid-morning. Aboveground activity is greatest during late summer and early autumn when juveniles become independent. Climate generally does not limit black-footed ferret activity, but it may remain inactive inside burrows for up to 6 days at a time during winter.
Female black-footed ferrets have smaller home ranges than males. Home ranges of males may sometimes include the home ranges of several females. Adult females usually occupy the same territory every year. A female that was tracked from December to March occupied . Her territory was overlapped by a resident male that occupied during the same period. The average density of black-footed ferrets near Meeteetse, Wyoming, is estimated at one black-footed ferret to . As of 1985, 40 to 60 black-footed ferrets occupied a total of of white-tailed prairie dog habitat. From 1982 to 1984, the average year-round movement of 15 black-footed ferrets between white-tailed prairie dog colonies was 1.6 miles/night (2.5 km) (with a spread of 1.1 miles or 1.7 km). Movement of black-footed ferrets between prairie dog colonies is influenced by factors including breeding activity, season, sex, intraspecific territoriality, prey density, and expansion of home ranges with declining population density. Movements of black-footed ferrets have been shown to increase during the breeding season; however, snow-tracking from December to March over a 4-year period near Meeteetse, Wyoming, revealed that factors other than breeding were responsible for movement distances.
Temperature is positively correlated with distance of black-footed ferret movement. Snow-tracking from December to March over a 4-year period near Meeteetse, Wyoming, revealed that movement distances were shortest during winter and longest between February and April, when black-footed ferrets were breeding and white-tailed prairie dogs emerged from hibernation. Nightly movement distance of 170 black-footed ferrets averaged (range ). Nightly activity areas of black-footed ferrets ranged from ), and were larger from February to March () than from December to January (). Adult females establish activity areas based on access to food for rearing young. Males establish activity areas to maximize access to females, resulting in larger activity areas than those of females.
Prey density may account for movement distances. Black-footed ferrets may travel up to to seek prey, suggesting that they will interchange freely among white-tailed prairie dog colonies that are less than apart. In areas of high prey density, black-footed ferret movements were nonlinear in character, probably to avoid predators. From December to March over a 4-year study period, black-footed ferrets investigated 68 white-tailed prairie dog holes per of travel/night. Distance traveled between white-tailed prairie dog burrows from December to March averaged over 149 track routes.
Reproduction and development
The reproductive physiology of the black-footed ferret is similar to that of the European polecat and the steppe polecat. It is probably polygynous, based on data collected from home range sizes, skewed sex ratios, and sexual dimorphism. Mating occurs in February and March. When a male and female in estrus encounter each other, the male sniffs the genital region of the female, but does not mount her until after a few hours have elapsed, which is in contrast to the more violent behavior displayed by the male European polecat. During copulation, the male grasps the female by the nape of the neck, with the copulatory tie lasting from 1.5 to 3.0 hours. Unlike other mustelids, the black-footed ferret is a habitat specialist with low reproductive rates. In captivity, gestation of black-footed ferrets lasts 42–45 days. Litter size ranges from one to five kits. Kits are born in May and June in prairie dog burrows. Kits are altricial and are raised by their mother for several months after birth. Kits first emerge above ground in July, at 6 weeks old.U.S. Fish and Wildlife Service. (1988). Species account: Black-footed ferret—Mustela nigripes, In: Endangered Species Program. Pierre, SD: U.S. Fish and Wildlife Service, Mountain-Prairie Region, South Dakota Ecological Services Field Office They are then separated into individual prairie dog burrows around their mother's burrow. Kits reach adult weight and become independent several months following birth, from late August to October. Sexual maturity occurs at the age of one year.
Intercolony dispersal of juvenile black-footed ferrets occurs several months after birth, from early September to early November. Dispersal distances may be short or long. Near Meeteetse, Wyoming, 9 juvenile males and three juvenile females dispersed following litter breakup. Four juvenile females dispersed a short distance (<), but remained on their natal area.
Diet