Threatened species of Mustela nigripes

The most endangered mammal in North America.

Declared extinct in 1979, conservation efforts allowed the black-footed ferret a comeback after a previously undiscovered colony of about a dozen individuals was found on a ranch in Meeteetse, Wyoming, just two years later. Today (2020), black-footed ferrets have been upgraded to the endangered species list with an estimated 206 black-footed ferrets alive in the wild and several hundred more in captivity.

Black footed ferrets have largely declined due to the loss of prey resulting from an extensive campaign to eradicate prairie dogs, mainly through poisoning. Canine distemper is fatal for Black-footed ferrets and it has decimated many populations and is a serious threat to reintroduced populations. Conversion of land to agricultural use has led to fragmentation of Black-footed ferret habitat. As ferrets live at low densities, a breeding population is spread over a large area, fragmentation reduces the populations ability to reproduce.

Presently restricted to reintroduction sites in Arizona, Montana, South Dakota and Wyoming, Black-footed ferrets formerly inhabited the Great Plains from Alberta, Canada, south through the intermontane regions of the Rocky Mountains to the south-western USA. In the 1800s, the ferret was widely distributed at low densities in ten states: Montana, Wyoming, North and South Dakota, Nebraska, Kansas, Colorado, New Mexico, Oklahoma, and northern Texas. It was also found in the extreme eastern portions of Utah and Arizona. In Canada, the species has not been recorded since 1937; by the 1950s it was believed to be extinct in the USA, until the discovery of a small population in South Dakota in the 1960s.

Sylvatic plague is a bacterial disease transmitted by fleas that afflicts many wild rodents, including both Black-footed ferrets and Prairie dogs. Black-footed ferrets use prairie dog burrows as dens to raise their young and escape larger predators or harsh weather. Prairie dogs also make up over 90% of the black-foot ferret’s diet. Not only does this disease have the ability to wipe out entire colonies of wild rodents after they’re re-introduced, the populations that do survive typically experience a reemergence 5–15 years after previous plague outbreaks.

Low genetic diversity is particularly problematic among Black-footed ferrets due to the fact that most of the world’s remaining individuals came from the original colony found in Wyoming. Gene diversity of the current captive population is estimated to be about 86% of the original gene diversity that was present in the population’s founders.

The last known wild population grew steadily from 60 in 1982 to 129 in 1984 as a result of protection. This trend came to an end in the summer of 1985 when canine distemper infected the ferrets and reduced the population to approximately 31. The remaining animals were captured for a captive breeding programme leaving no known wild population; six died in captivity and the global population of the species in 1985 totalled 25 Between 1991 and 1997 over 200 ferrets have been released back into the wild.

The IUCN considers Mustela nigripes as "Extincnt in the Wild". CITES lists the species as "Appendix 1".