W6 



Miunmals — Our Livuig Resources 



Black-footed 

 Ferrets 



hy 



Dean Biggins 



Jerry Godhey 

 National Biological Service 



120- 



100- 



,80- 



5 60- 



" 40 

 20 

 0- 



H 



<1900 00-19 20-39 40-59 60-79 

 Years 



Fig. 1. Black-tooted lerrets col- 

 lected before IMSO, 



— 3 



83 84 85 86 87 88 89 90 91 92 

 Year 



Fig. 2. Black-footed ferret popu- 

 lation from Meeteetse. Wyoming, 

 1983-92 (all captive from 1986 to 

 present). 



The hiack-footed feiTet (Mustehi iiiiiripcs) 

 was a charter member of endangered 

 species lists for North America, recognized as 

 rare long before the passage of the Endangered 

 Species Act of 1 973. This member of the weasel 

 family is closely associated with prairie dogs 

 iCynonixs spp.) of three species, a specializa- 

 tion thai contributed to its downfall. Prairie 

 dogs make up 9()'7( of the feuet diet: in addition, 

 tenets dwell in prairie dog buiTOWs during day- 

 light, venturing out mostly during darkness. 

 Trappers captured black-footed tenets during 

 their quests for other species of furbearers. 

 Although the species received increased atten- 

 tion as it became increasingly rare, the number 

 of documented ferrets fell steadily after 1940 

 (Fig. I ). 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^he 1920"sand 193()'s. 



Much of what is known about black-footed 

 fen'et biology was learned from research during 

 1964-74 on a remnant population in Scnith 

 Dakota (Linder et al. 1972; Hillman and Linder 

 1973). and from 1981 to the present on a popu- 

 lation found at Meeteetse, Wyoming, and later 

 transferred to captivity (Biggins et al. 1985; 

 Fon-est et al. 1988; Williams et al. 1988). Nine 

 ferrets from the sparse South Dakota population 

 (only 1 1 feiTet litters were located during 1964- 

 72) were taken into captivity from 1971 to 

 1973, and captive breeding was undertaken at 

 the U.S. Fish and Wildlife Service's Patuxent 

 Wildlife Research Center in Maryland 

 (Caipenter and Hillman 1978). Although litters 

 were born there, no young were successfully 

 raised. The last of the Patu.xent captive ferrets 

 died in 1978. and no animals were located in 

 South Dakota after 1979. 



Black-footed feirets were "rediscovered" in 

 prairie dog complexes at Meeteetse in 1981. 

 giving conservationists what seemed a last 

 chance to learn about the species and possibly 

 save it from extinction. That population 

 remained healthy (70 feiTet litters were counted 

 from 1982 to 1986) through 1984 (Fig. 2). a 

 period when much was learned about ferret life 

 history and behavior. In 1985, sylvatic plague, a 

 disease deadly to prairie dogs, was confirmed in 

 the prairie dogs at Meeteetse, creating fear that 

 the prairie dog habitat vital for tenets would be 

 lost. In addition, field biologists were reporting 

 a substantial decrease in the number of ferrets 

 detected. The fear of plague was quickly over- 

 shadowed by the discovery of canine distemper 

 in the feiTets themselves. It is a disease lethal to 

 ferrets. 



In 1985 six ferrets were captured to begin cap- 



Black-footed ferrets, almost c\tinct by 1985. are bemg 

 reintroduced from captive breeding but still lack genetic 

 diversity. 



tive breeding, but two of ihcm brought the dis- 

 temper virus into captivity, and all six died 

 (Williams et al. 1988). A plan was formulated to 

 place more animals from Meeteetse into captivi- 

 ty to protect them from distemper and to start the 

 breeding program. By December 1985, only 10 

 ferrets were known to exist. 6 in captivity and 4 

 at Meeteetse. The following year, the surviving 

 free-ranging ferrets at Meeteetse produced only 

 two litters, a number thcuight too small to sustain 

 the wild population. Because both the Meeteetse 

 and captive populations were too small to sustain 

 themselves, all remaining fen'ets were removed 

 from the wild, resulting in a captive population of 

 18 individuals by early 1987. 



Captive breeding of ferrets eventually 

 became successful (Fig. 2). Although the captive 

 population is growing, researchers fear the con- 

 sequences of low genetic diversity (already doc- 

 umented by O'Brien et al. 1989) and of inbreed- 

 ing depression {see glossary). A goal of the 

 breeding program is to retain as much genetic 

 diversity as possible, but the only practical way 

 to increase diversity is to find more wild feirets. 

 In spite of intensive searches of the remaining 

 good ferret habitat and investigations of sighting 

 reports, no wild ferrets have been found. 



The captive breeding program now is pro- 

 ducing sufficient surplus feiTets for reintroduc- 

 tion into the wild; 187 ferrets were released into 

 prairie dog colonies in Shirley Basin. Wyoming, 

 during 1991-93. Challenges facing the black- 

 footed ferret reintroduction include low sur- 

 vivorship of released feiTets due to high disper- 

 sal and losses to other predators; unknown 

 infiuence of low genetic diversity; canine dis- 

 temper hazard; indirect effect of plague on 

 prairie dogs and possible direct effect on ferrets; 

 and low availability of suitable habitat for rein- 

 troduction. The scarcity of habitat reflects a 

 much larger problem with the prairie dog 

 ecosystem and needs increased attention. 



At the turn of this century, prairie dogs 

 reportedly occupied more than 4() million ha 



