Exploring dietary specialization of black-footed ferrets (Mustela nigripes)

Abstract

It is widely accepted that black-footed ferrets (Mustela nigripes) are an obligate dietary specialist of prairie dogs (Cynomys spp.). Indeed, the extirpation of ferrets from the wild was attributed to the decline of prairie dogs throughout North America. However, the degree to which ferrets are specialized predators of prairie dogs and their foraging plasticity is unclear. We quantified the diet of free-ranging black footed ferrets in Wyoming, USA using stable isotope analysis. We also explored different age-sex group dietary differences based on sexual size dimorphism. Our results confirmed that prairie dogs were the most important diet item, although ferrets also displayed greater foraging plasticity than previously believed and consumed large quantities of species of smail mammals. The degree to which ferrets specialized on prairie dogs also differed between ferret age-sex groups. Adult male and juvenile ferrets possessed roughly equivalent diets, with prairie dogs constituting nearly 75% of their assimilated diet. In contrast, adult female ferrets relied less on prairie dogs (63%), and more heavily on smaller-bodied mice(31 %). These results suggest that intraspecific competition is limited by sexual size dimorphism, with larger males consuming the larger-bodied prairie dogs more than adult females. Prairie dogs were, however, a critical nutritional component for young, and female ferrets appear to have preferentially provided prairie dogs to their offspring, rather than consuming in their own diet. Conservation of prairie dogs colonies, not just as prey items, but also for the prey-rich habitat they provide will be key for saving one of North America's most endangered mammals.