Twenty-nine years after listing, this two-pound weasel remains the rarest mammal in North America. Introduced diseases and a century of prairie dog control have brought it to the brink of extinction.
With the death of the last of nine captive ferrets at Patuxent Wildlife Research Center in 1978, most people feared the species had become extinct. Then in 1981, hopes were buoyed by discovery of a new population near Meeteetse, Wyoming (129 ferrets observed over a five-year period). Unfortunately, these ferrets, and the prairie dogs on which they preyed, were soon ravaged by sylvatic plague and canine distemper.
Again fearing extirpation of the species, biologists rounded up the 18 survivors. These became founders of a captive population that today numbers close to 300. For safety, these ferrets are now housed in nine facilities in six states and Canada.
Three free-roaming populations have been started by reintroducing animals from this captive population. In 1991, 49 ferrets were released into white-tailed prairie dog towns in Wyoming's Shirley Basin. Not unexpectedly, predation and starvation took a heavy toll. Additional ferrets were released there in 1992, 1993, and 1994.
In 1994 ferrets were also released into black-tailed prairie dog towns in Badlands National Park, South Dakota, and in northeastern Montana's C.M. Russell National Wildlife Refuge. Last summer, prior to additional releases in South Dakota and Montana (the Shirley Basin population was not augmented in 1995), the three populations contained about 10 ferrets each. Montana's first release in 1994 followed long discussions involving local ranchers, tribal leaders, the Bureau of Land Management (BLM), U.S. Fish and Wildlife Service (USFWS), National Biological Service (NBS), and Montana Fish, Wildlife & Parks (FWP). Of 35 kits and five adults released in October, only eight ferrets could be located in December. In spring of 1995, two or possibly three pairs produced at least five new kits.
In fall of 1995, an additional 36 ferrets were released in another prairie dog town several miles from the first site. Prior to this release, 66 coyotes were removed from a 50-section area surrounding the site, and an electric fence was strung around the prairie dog town for a few weeks to deter predators. In December of 1995, a survey of both release sites documented 24 ferrets (eight at the first site and 16 at the second).
None of the three reintroduced ferret populations is well established at this time, and there is ongoing concern about the genetic viability of the captive population. The search continues for undiscovered black-footed ferret populations, but hopes are dampened by the knowledge that less than 8% of North America's historic prairie dog acreage remains.
In Montana, the goal is to reestablish two viable populations with a minimum of 50 breeding adults in each. Nationwide, the objective is to increase the captive population to 250 breeding adults and to establish a wild pre-breeding population of 1,500 adults in 10 or more locations by 2010.