Introduction

The black-footed ferret (Mustela nigripes) is one of the world's most critically endangered mammals. Until about 1920, the carnivorous ferret occupied nearly 40 million ha over 12 Great Plains and Rocky Mountain states and two Canadian provinces. Agricultural interests and federal and state rodent control programs drastically eliminated ferret habitat–prairie dog (Cynomys spp.) colonies (the ‘prairie dog ecosystem’, Clark, Hinckley & Rich 1989b)–and fragmented the remainder into small patches, thus rendering isolated ferret populations highly vulnerable to extinction from various causes, including local catastrophes. Extensive searches in the late 1970s yielded no ferrets, and they were feared extinct, but in 1981 a small population was found near Meeteetse in northwestern Wyoming. By early 1986, only about ten individual ferrets were known, four in the wild and six in a single captive breeding facility. Fortunately, as of January, 1992, there were 175 ferrets in six captive breeding facilities, and 49 ferrets had been introduced to the wild. There is every reason to believe that the ferret will eventually be restored to the wild in viable numbers and distributions. Overviews of the ferret and prairie dog conservation and management effort are given by Casey, DuWaldt & Clark (1986), Clark (1986a), and Reading & Clark (1990).

The ferret's conservation history has been complex and unpromising. Both the ferret and determination of its critical habitat ranked very high in the first US Redbook of Endangered Wildlife in 1964, and again in a US Fish and Wildlife Service list of endangered species priorities in 1976.