Animal Field Guide

Black-footed Ferret

Mustela nigripes
(Mustelidae)

Montana Species of Concern
Global Rank: G1
State Rank: S1

Agency Status
USFWS: LE,XN
USFS: ENDANGERED
BLM: SPECIAL STATUS

Black-footed ferrets are weasel-like in body shape and form but are heavier than other weasels. The torso is long with short legs and a long tail. The color of the body is a soft cream color with the ears, chin and throat fading to white. The dorsal portion of the torso is darker than the rest of the body. The legs and tip of the tail are dark brown and a mask of the same color extends in a band from below each eye across the forehead.

Although similar in size and shape to the mink (Mustela vison), the much lighter body color and prairie habitat of the black-footed ferret are distinctive. Long-tailed weasels (Mustela frenata) are smaller and less robust and do not have the distinctive black mask and feet of the ferret.

Black-footed ferrets are not known to migrate. Juveniles disperse in September. Adults use about a 100-acre range semi-nomadically (Richardson 1986).

Black-footed ferrets are intimately tied to prairie dogs (Cynomys spp.) throughout their range and have only been found in association with prairie dogs. They are therefore limited to the same open habitat used by prairie dogs: grasslands, steppe, and shrub steppe. Black-footed ferrets do not dig their own burrows and rely on abandoned prairie dog burrows for shelter. Only large complexes (several thousand acres of closely spaced colonies) can support and sustain a breeding population of black-footed ferrets. It has been estimated that about 40 to 60 hectares of prairie dog colony is needed to support one ferret, and females with litters have never been found on colonies less than 49 hectares (Miller et al. 1996). Ferrets scent-mark to maintain spatial separation (Richardson 1986).

Prairie dogs are an important food source; one study found prairie dog remains in 91% of analyzed ferret scats (Hillman and Clark 1980). Alternate prey such as ground squirrels, rabbits, voles and mice are probably eaten opportunistically.

Black-footed ferrets eat and defecate underground. They sometimes drag prey more than 1000 feet in winter. Ferrets travel an average of 1 mile per night. They do not adopt one "den burrow" and are semi-nomadic, traveling from burrow to burrow (Richardson 1986).

No specific information on black-footed ferret reproductive biology is available for Montana, but in other portions of their range copulation occurred in March and early April. Gestation is 42 and 45 days (Foresman 2001). Wild-born litter sizes in South Dakota averaged 3.5 (range 1 to 5) (Hillman and Clark 1980), and 3.3 at emergence in Wyoming (Forrest et al. 1988). Young are born underground in prairie dog burrows. Young appear above ground usually in July and disperse in fall. At least some females reproduce as yearlings (Forrest et al. 1988).

Black-footed ferrets have been extirpated from most of their former large range mainly as a result of prairie dog and predator control programs. Canine distemper, in conjunction with captures for captive breeding, resulted in extirpation of the last known wild population near Meeteetse, Wyoming by early 1987. See Miller et al. (1996) for more information on the discovery of the Meeteetse ferrets and subsequent distemper-caused decline and captive breeding decisions that occurred in 1985. All known populations are a result of the reintroduction of captive bred ferrets from animals taken into captivity from this population. Reintroductions have occurred annually in Montana on federal and/or tribal land since 1994 with varying success. Predation by coyotes and badgers, and long distance dispersal have been the primary problems with the reintroduction efforts, but plague has also apparently resulted in deaths for released animals. Some wild reproduction has occurred but no self-sustaining populations have been established yet.