About Mustela nigripes (Audubon & Bachman, 1851)
This species is the black-footed ferret, with the scientific name Mustela nigripes (Audubon & Bachman, 1851). It has a long, slender body, with distinct black markings on its paws, ears, parts of its face, and tail. Its forehead is broad and arched, and its muzzle is short; it has few whiskers. Its ears are triangular, short, erect, and broad at the base. It has a long neck, short stout legs, and toes bearing sharp, very slightly curved claws. Hair covers both surfaces of the feet, all the way to the soles, hiding the claws. It combines physical traits seen in both members of the weasel subgenus Gale (least weasels and short-tailed weasels) and the polecat subgenus Putorius (European polecats and steppe polecats). Its skull matches polecat skulls in size, massiveness, and the development of ridges and depressions, but it can be distinguished by an extremely narrow constriction behind the eye sockets, where the cranium is far narrower than the muzzle. While it is similar in size to polecats, its slender body, long neck, very short legs, narrow tail, large round ears, and tightly packed fur give it a conformation much closer to weasels and stoats. Its dentition very closely resembles that of the European and steppe polecat, except the lower back molar is vestigial. This molar has a hemispherical crown that is too small and weak to develop the small distinct cusps that are clearly visible in polecats. It differs from the European polecat by having stronger contrast between its dark limbs and pale body, and a shorter black tail tip. Differences from the Asian steppe polecat are very small, so much so that the two species were once considered to be the same species. The only clear differences between black-footed ferrets and steppe polecats are that black-footed ferrets have much shorter, coarser fur, larger ears, and a longer post-molar extension of the palate. Male black-footed ferrets measure 500–533 millimeters (19.7–21.0 inches) in body length, with a 114–127 millimeter (4.5–5.0 inch) tail, which makes up 22–25% of total body length. Females are typically 10% smaller than males. The species weighs 650–1,400 grams (1.43–3.09 pounds). Captive-bred ferrets raised for reintroduction projects are smaller than wild black-footed ferrets, but these individuals quickly reach the historical species body size after release. The base fur color is pale yellowish or buff across both the upper and lower body. The top of the head, and sometimes the neck, is darkened by dark-tipped hairs. A wide band of sooty black crosses the face, covering the eyes. The feet, lower legs, tail tip, and preputial region are also sooty-black. A large patch of dark umber-brown marks the area midway between the front and back legs, fading into the surrounding buff-colored fur. There is a small pale spot above each eye, and a narrow pale band behind the black facial mask. The sides of the head and ears are dirty-white. Historically, the black-footed ferret's range closely matched (but was not restricted to) the range of prairie dogs (Cynomys spp.), extending from southern Alberta and southern Saskatchewan in Canada south to Texas, New Mexico, and Arizona in the United States. As of 2007, the only known wild black-footed ferret population was located on approximately 6,000 acres (2,400 hectares) in the western Big Horn Basin near Meeteetse, Wyoming. Starting in 1990, black-footed ferrets have been reintroduced to multiple sites: Shirley Basin, Wyoming; UL Bend National Wildlife Refuge and Fort Belknap Indian Reservation, Montana; Conata Basin/Badlands, Buffalo Gap National Grassland, Wind Cave National Park, and the Cheyenne River Sioux Reservation in South Dakota; Aubrey Valley, Arizona; Rocky Mountain Arsenal National Wildlife Refuge and Wolf Creek in Colorado; Coyote Basin, which spans Colorado and Utah; northern Chihuahua, Mexico; and Grasslands National Park, Canada. Historical habitats for the species include shortgrass prairie, mixed-grass prairie, desert grassland, shrub steppe, sagebrush steppe, mountain grassland, and semi-arid grassland. Black-footed ferrets use prairie dog burrows to raise young, avoid predators, and get thermal cover. Six black-footed ferret nests found near Mellette County, South Dakota, were lined with buffalo grass, prairie threeawn, sixweeks grass, and cheatgrass. High densities of prairie dog burrows provide the greatest amount of cover for black-footed ferrets. Black-tailed prairie dog colonies have higher burrow density per acre than white-tailed prairie dog colonies, and may be more suitable for black-footed ferret recovery. Burrow type may affect whether black-footed ferrets occupy a site. Near Meeteetse, Wyoming, black-footed ferret litters were associated with mounded white-tailed prairie dog burrows, which are less common than non-mounded burrows. Mounded burrows have multiple entrances, and likely have a deep, extensive burrow system that protects young ferret kits. Even so, near Meeteetse, Wyoming, black-footed ferrets used non-mounded prairie dog burrows (64% of occurrences) more often than mounded burrows (30% of occurrences). The reproductive physiology of the black-footed ferret is similar to that of the European polecat and steppe polecat. It is likely polygynous, based on data from home range sizes, skewed sex ratios, and sexual dimorphism. Mating takes place in February and March. When a male encounters a female in estrus, he sniffs her genital region, but does not mount her until several hours later. This differs from the more aggressive mating behavior of male European polecats. During copulation, the male grasps the female by the nape of the neck, and the copulatory tie lasts between 1.5 and 3.0 hours. Unlike many other mustelids, the black-footed ferret is a habitat specialist with low reproductive rates. In captivity, gestation lasts 42–45 days. Litter size ranges from one to five kits. Kits are born in May and June inside prairie dog burrows. Kits are altricial, and are raised solely by their mother for several months after birth. Kits first emerge above ground in July, when they are 6 weeks old. After emerging, each kit moves into its own separate prairie dog burrow near their mother's burrow. Kits reach adult weight and become independent several months after birth, between late August and October. Sexual maturity is reached at one year of age. Juvenile black-footed ferrets disperse between prairie dog colonies several months after birth, from early September to early November. Dispersal distances can be either short or long. Near Meeteetse, Wyoming, 9 juvenile males and 3 juvenile females dispersed 1 to 4 miles (1.6 to 6.4 km) after their litter split up. Four juvenile females dispersed less than 0.2 miles (0.32 km), and stayed within their natal area.
