The black-footed ferret (Mustela nigripes) was a charter member of endangered species lists for North America, recognized as rare long before the passage of Endangered Species Act of 1973. This member of the weasel family is closely associated with prairie dogs (Cynomys spp.) of three species, a specialization that contributed to its downfall. Prairie dogs make up 90% of the ferret diet; in addition, ferrets dwell in prairie dog burrows during daylight, venturing out mostly during darkness. Trappers captured black-footed ferrets during their quests for other species of furbearers. Although the species received increased attention as it became increasingly rare, the number of documented ferrets fell steadily after 1940 (Fig. 1), and little was learned about the animals before large habitat declines made studies of them difficult. These declines were brought about mainly by prairie dog control campaigns begun before 1900 and reaching high intensity by the 1920’s and 1930’s.
