The Cranial Morphology of the Black-Footed Ferret: A Comparison of Wild and Captive Specimens

SIMPLE SUMMARY: The black-footed ferret, a member of the weasel family originally found throughout much of Midwestern North America, nearly went extinct prior to the 1980s, in part because of ranchers’ persecution of prairie dogs, which make up almost all of the ferret’s natural diet. In the 1980s, the few remaining wild individuals of the species were brought into captivity in an effort to breed enough animals to reintroduce a more stable population back into the wild. While this program was successful in expanding the numbers of animals enough to release animals back into the wild, the diet of the captive animals was so substantially different that it caused dramatic dental issues. In the current study, we examined the skulls of 271 adult ferrets and 53 specimens of two species that are closely related to ferrets and found that the captive ferrets differ substantially in skull shape from the wild individuals and that some of these differences are even more substantial than some of the differences between black-footed ferrets and their relatives. Thus, captivity (probably the captive diet) has a substantial negative effect on not only the oral health (gum disease, cavities, etc.) but also on skull shape as well. ABSTRACT: The black-footed ferret (Mustela nigripes), a North American mustelid species, was once found abundantly throughout the Midwest until the extreme decline in prairie dogs (Cynomys spp.), the black-footed ferret’s primary food source, brought the species to near-extinction. Subsequently, the Black-Footed Ferret Recovery Program was created in the 1980s with a goal of bringing all remaining individuals of the species into captivity in order to breed the species back to a sustainable population level for successful reintroduction into the wild. While many components of the ferrets’ health were accounted for while in captivity—especially those affecting fecundity—this study aims to assess the effects that captivity may have had on their cranial morphology, something that has not been widely studied in the species. In a previous study, we showed that the captive ferrets had significant oral health problems, and here we aim to document how the captive diet also affected their skull shape. For this study, 23 cranial measurements were taken on the skulls of 271 adult black-footed ferrets and 53 specimens of two closely related species. Skulls were divided based on sex, species, captivity status and phase of captivity and compared for all measurements using stepwise discriminant analysis as well as principal component analysis derived from the combined variables. We found that there are significant differences between captive and wild specimens, some of which are larger than interspecific variation, and that a diet change in the captive specimens likely helped decrease some of these differences. The results suggest that captivity can cause unnatural cranial development and that diet likely has a major impact on cranial morphology.