By Pete Gober and Mike Lockhart

The black-footed ferret (Mustela nigripes) evolved on the North American prairie when the prairie dog (Cynomys sp.), the prey on which the ferret depends, inhabited approximately 100 million acres (2.5 million hectares). The historical range of ferrets and prairie dogs roughly overlapped and extended over 12 States, from western Canada to Mexico, although the ferret was never a commonly observed animal. Prairie dog habitat has been reduced by about 98 percent from former levels. What remains is fragmented into remnants of various size.

A black-footed ferret can be a prairie dog's worst nightmare, but recovery efforts for the ferret promote the conservation of prairie dog species and prairie ecosystems by focusing on the common needs of these closely associated mammals. USFWS Photo

Reductions in occupied prairie dog habitat resulted initially from the conversion of native prairies to other uses, primarily relating to farming. Subsequent losses resulted from widespread poisoning programs intended to reduce competition between prairie dogs and domestic livestock for forage, and more recently from the impacts of sylvatic plague (an Old World disease introduced into North America at the turn of the century). All of these factors continue to influence prairie dog populations, which in turn influence black-footed ferret populations.

One of the last known populations of ferrets was extirpated in South Dakota during the early 1970's. The species was feared to be extinct until a small population was found in northwestern Wyoming in 1981. This population was monitored for several years but soon was decimated by disease. Before the ferret population disappeared, a few animals were salvaged for a captive breeding effort conducted by the Wyoming Game and Fish Department, the Fish and Wildlife Service, participating institutions of the American Zoo and Aquarium Association, and other cooperators. Successes in the captive breeding program allowed biologists to initiate reintroduction at a south-central Wyoming site in 1991. Unfortunately, however, the reintroduction efforts in Wyoming were limited by disease and other factors, and the program in that area was suspended in 1995.

Additional reintroduction efforts began in Montana and South Dakota in 1994 and have continued through 1996. Ferrets released in these States appear to have had higher survival rates than those in Wyoming and have not been impacted by disease to date. Approximately 60 ferrets, including reintroduced captive-born animals and their offspring born in the wild, existed in Montana and South Dakota prior to the release of additional captive-born ferrets in 1996.

Higher ferret survival and productivity rates at the Montana and South Dakota sites are likely associated with the occurrence of more densely populated black-tail prairie dog (Cynomys ludovicianus) towns there, as opposed to the white-tailed prairie dog (Cynomys leucurus) habitats found at the Wyoming reintroduction site. Improved success also may be the result of "preconditioning" the ferrets in large outdoor pens inhabited by prairie dogs. Animals prepared in this manner had significantly higher survival rates 30 days after their release than cage-reared ferrets.

Captive breeding and reintroduction projects are the backbone of the national Black-footed Ferret Recovery Program. Some 20 State and Federal agencies, along with several non-governmental organizations, spend about $1.5 million annually on ferret recovery ventures. Although the program has made substantial strides, the total number of ferrets is still quite small (less than 600), and both captive and reintroduced populations are susceptible to catastrophic events.

Prairie dog colonies were integral components of the prairie ecosystem as it once existed across the Plains States. USFWS Photo

The plight of the ferret is only part of a greater issue, the loss of a largely unrecognized but perhaps equally important and threatened resource--prairie dog towns. Prairie dogs occur on a variety of prairie and high desert vegetative communities. Their towns provide food and habitat for a diverse community of wildlife species. Prairie dogs are consumed by a variety of avian and mammalian predators including the coyote (Canis latrans), badger (Taxidea taxus), swift fox (Vulpes velox), golden eagle (Aquila chrysaetos), ferruginous hawk (Buteo regalis), and red-tailed hawk (Buteo jamaicensis). In some locations, even wintering bald eagles (Haliaeetus leucocephalus) make their living by robbing hawks that are more successful at catching prairie dogs.

The burrows of prairie dogs are used as shelter and hibernation chambers for many species of snakes, lizards, and amphibians. In portions of the west, burrowing owls (Speotyto cunicularia) also depend completely on prairie dog towns, using their holes for nest sites. The associated denuded lands also expose potential enemies and the prey animals on which the owls feed. The burrowing owl is in serious decline throughout many parts of its range in direct response to losses of prairie dog colonies. Like the burrowing owl, the mountain plover (Eupoda montana) is also attracted to short grass or barren areas and is closely associated with prairie dog towns throughout much of its range.

Prairie dogs clip tall-growing vegetation within their towns to enhance predator detection. The rather barren appearance of the landscape surrounding prairie dog towns and the associated loss of vegetation have earned prairie dogs the reputation as vermin. Many people consider land þruinedþ by the presence of prairie dogs, and several States still promote their eradication. However, recent information suggests that prairie dogs are a vital part of the ecology of native grasses, and that burrowing and mixing of soil constituents are important for maintaining the long-term viability of prairie soils.

Among the species associated with prairie dogs that have declined along with the ferret are the ferruginous hawk, burrowing owl, swift fox, and mountain plover. The plover and fox are even candidates for listing under the Endangered Species Act. Although the presence of prairie dogs is not compatible with many agricultural uses, there is hope that enough of these animals can be conserved on public lands to ensure the survival and recovery of the black-footed ferret and associated prairie species.

Pete Gober, the FWS Black-footed Ferret Recovery Coordinator, is located in the Pierre, South Dakota, Field Office. Mike Lockhart, also with the ferret recovery program, is in the FWS Laramie, Wyoming office

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