Endangered species taken captive for breeding and then reintroduced to the wild commonly fail to produce self-sustaining populations.
Such failures result from the persistence of environmental factors that caused the species to become endangered in the first place.
- inbreeding in small populations
- behavioral and physiological consequences of a captive environment
However, first reintroduced population of the most endangered mammal species in North America, the blackfooted ferret (Mustela nigripes), is recovering rapidly in the Shirley Basin of Wyoming after a lag that seemed to portend population extinction. Population recovery notable because bottleneck of the 1980s reduced genetic variability and captive breeding affected various phenotypic traits. Also, two potentially devastating infectious diseases, plague and canine distemper, occurred shortly after the releases.
Primary prey at this site is the white-tailed prairie dog, considered suboptimal because it hibernates for extended periods and has low population densities.
Last known wild population of ferrets, discovered in 1981 near Meeteetse, Wyoming, basis for the captive breeding program.
- From seven genetic founders in 1987, over 4800 juveniles have been produced, and many were reintroduced to sites in the ferret’s historical range.
- Shirley Basin received 228 captive-born animals during 1991–1994, but due to dieseases only 5 were found by 1997.
- In 2003, surveys revealed a surprising increase to 52 animals, and monitoring intensified.
Ferrets potential for rapid population growth seems to contradict the slow life history strategy common to endangered vertebrates.
Matrix population model based on estimates of vital rates (including birthrates, survival rates, and mortality rates) revealed unexpected attributes
- Analysis showed that success in the first year of life is the key to demographic success
- Early survival and recruitment are the crucial factors in this animal’s life history, rather than the later adult survival that commonly matters to endangered species
Black-footed ferrets have bred successfully in the wild for 7.5 generations, largely obviating fears that inbreeding depression
or captive propagation would impair population establishment or short-term persistence.
Vulnerabilities to infectious diseases and potential declines of prairie dog populations remain serious concerns.
Shirley Basin example shows that species recovery is possible, given the ferret’s capacity to persist at low population levels and to increase rapidly in favorable environments.