Ferrets
Ferrets
An experiment in captive breeding
Ferrets are small carnivores belonging to the weasel family (Mustelidae). The name is most commonly given to the fitch, or European polecat (Mustela putorius ), which has been domesticated and used for hunting rodents and as a pet for hundreds of years. Like most weasels, ferrets are long and slender, and are determined hunters. Their color varies from yellowish to all black, and they are about 2 ft (60 cm) long, including the tail. Like all weasels, the male is considerably larger than the female.
In North America, a close relative of the European polecat inhabits prairie habitat. The black-footed ferret (Mustela nigripes ) looks like its European relative, but all four feet are black under a yellowish or tan body. It also has a black mask on its small, triangular head and a black tip on its tail, whereas the tail of the polecat is entirely dark.
The black-footed ferret is probably descended from the steppe polecat (Mustela eversmanni ) of Russia, which looks almost identical and leads a similar life in open grassland. However, the steppe polecat is still numerous, and even welcomed by people because it eats rodent pests. The black-footed ferret has developed specialized eating habits that place its future survival in jeopardy.
The black-footed ferret lives in close association with prairie dogs (Cynomys spp.). It depends on these rodents as a source of food and also uses their burrows for shelter. Over many decades, prairie dogs throughout their range have been killed by poisoned grain spread by farmers determined to keep these rodents from tearing up their land when they dig their burrows. As the prairie dogs have disappeared, so has the black-footed ferret.
Ferrets are solitary animals, except during the spring mating season. One to six kits are born after a gestation period of about six weeks. Males do not help females raise the young. Young ferrets begin to venture out of their burrow in July. One of their first trips out might be to a nearby burrow where their mother has placed a dead prairie dog for them to eat. She will continue to provide them with meat until they are able to hunt on their own in the autumn.
As prairie dogs were eradicated from most of the American prairie, young ferrets in search of territory after separating from their mother often could not find a new prairie-dog colony to inhabit. Or if they could find a new colony, it was too isolated from other ferrets for breeding to occur. Populations of black-footed ferrets dwindled, and by the 1960s it was clear that there were very few of these animals left in the wild. In fact, the species was considered extinct.
An experiment in captive breeding
Fortunately, in 1981 a tiny population of nine black-footed ferrets was found in the Absaroka Mountains of Wyoming. These animals were protected, and the number quickly grew to more than 100. Unfortunately, an introduced disease (canine distemper) then killed all but 18 animals. The few survivors were taken into captivity by the U.S. Fish and Wildlife Service to establish a captive breeding program, in a last-ditch effort to save the black-footed ferret from extinction. Part of the attempt to save the species involved studies of the steppe polecat, to learn about the biology and behavior of this closely related animal. This information was then applied to breeding the black-footed ferret in captivity.
By 1987, several captive ferrets had succeeded in raising young. The captive population increased during the next several years, and by 1996 there were more than 500 black-footed ferrets in captivity. Since 1991, several hundred black-footed ferrets have been returned to the wild, mostly in Wyoming, Utah, Colorado, and South Dakota. About 850 black-footed ferrets now exist in both the reintroduced and captive populations.
A new threat to the prairie dog and black-footed ferret populations is the spread of a plague (Yersinia pestis ) into their habitat. This bacterial infection is approaching the Conata Basin in South Dakota, an area that supports the largest black-footed ferret population in the United States. In an attempt to prevent plague infection in Conata, biologists dusted prairie dog burrows with an insecticide to kill the fleas that carry the plague bacteria in the fall of 2005. It is not yet known whether this measure has been successful and biologists continue weekly patrols of the area watching for dead prairie dogs. If a plague outbreak does occur,
the biologists will probably begin to remove and/or vaccinate the ferrets in the Conata population.
The goal of the captive-breeding program is to maintain a viable population of black-footed ferrets in captivity, and to provide stock for reintroduction to the wild. By the year 2010, the U.S. Fish and Wildlife Service hopes to have established 10 wild populations of black-footed ferrets, comprised of a total of 1,500 individuals, and spread widely within their former range. The Canadian Wildlife Service also intends to reintroduce this endangered species into southern Saskatchewan. It will take many years and good stewardship by landowners to determine whether the reintroduction of black-footed ferrets into the American prairie will succeed. The black-footed ferret continues to be considered an endangered species by all conservation organizations, including the U.S. Fish and Wildlife Service.
See also Weasels.
Resources
BOOKS
Burton, John A., and Bruce Pearson. The Collins Guide to the Rare Mammals of the World. Lexington, MA: Stephen Greene Press, 1987.
Casey, Denise. Black-footed Ferret. New York: Dodd, Mead & Company, 1985.
Fox, J.G., ed. Biology and Diseases of the Ferret. Lippincott, Williams & Wilkins, 1998.
Knight, Lindsay. The Sierra Club Book of Small Mammals. San Francisco: Sierra Club Books, 1993.
Nowak, Ronald M., ed. Walker’s Mammals of the World. 6th ed. Baltimore: Johns Hopkins University Press, 1999.
Schreiber, A., et al. Weasels, Civets, Mongooses and Their Relatives: An Action Plan for the Conservation of Mustelids and Viverrids. Gland, Switzerland: IUCN-The World Conservation Union, 1989.
Jean F. Blashfield