The black-footed ferret 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.[6][7] Up to 90% of its diet is composed of prairie dogs.[8][9]
The species 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 Meeteetse, Wyoming in 1981.[10] 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. As of 2015, over 200 mature individuals are in the wild across 18 populations, with four self-sustaining populations in South Dakota, Arizona, and Wyoming.[1][11] It was first listed as "endangered" in 1982, then listed as "extinct in the wild" in 1996 before being upgraded back to "endangered" in the IUCN Red List in 2008.[1] In February 2021, the first successful clone of a black-footed ferret, a female named Elizabeth Ann, was introduced to the public.[12]
Evolution[edit]
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.[4] 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.[13] 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.[14] 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.[15] 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.[14] 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.[15][13]
Mortality[edit]
Primary causes of mortality include habitat loss, human-introduced diseases, and indirect poisoning from prairie dog control measures.[9][21][23][25] Annual mortality of juvenile and adult black-footed ferrets over a 4-year period ranged from 59 to 83% (128 individuals) near Meeteetse, Wyoming.[24] During fall and winter, 50–70% of juveniles and older animals perish.[24] Average lifespan in the wild is probably only one year, but may be up to five years. Males have higher rates of mortality than females because of longer dispersal distances when they are most vulnerable to predators.[24]
Given an obligate dependence of black-footed ferrets on prairie dogs, black-footed ferrets are extremely vulnerable to prairie dog habitat loss. Habitat loss results from agriculture, livestock use, and other development.[25]
Black-footed ferrets are susceptible to numerous diseases. They are fatally susceptible to canine distemper virus,[15][24] introduced by striped skunks, common raccoons, red foxes, coyotes, and American badgers.[23] A short-term vaccine for canine distemper is available for captive black-footed ferrets, but no protection is available for young born in the wild. Black-footed ferrets are also susceptible to rabies, tularemia, and human influenza. They can directly contract sylvatic plague (Yersinia pestis), and epidemics in prairie dog towns may completely destroy the ferrets' prey base.[29]
Predators of black-footed ferrets include golden eagles, great horned owls, coyotes, American badgers, bobcats, prairie falcons, ferruginous hawks, and prairie rattlesnakes.[9][23][24]
Oil and natural gas exploration and extraction can have detrimental impacts on prairie dogs and black-footed ferrets. Seismic activity collapses prairie dog burrows. Other problems include potential leaks and spills, increased roads and fences, increased vehicle traffic and human presence, and an increased number of raptor perching sites on power poles. Traps set for coyotes, American mink, and other animals may harm black-footed ferrets.[8]