Black-footed ferret Mustela nigripes energy expenditure and prey requirements

Abstract

Black-footed ferrets Mustela nigripes are exceedingly rare and only a single extant population in Wyoming is known. Tracks in the snow and direct observations have provided data on activity and show that a ferret can travel from 0 to 7 km and may move up to 50 litres of soil from prairie dog Cynomys spp. burrows in a night. We constructed an additive model to estimate ferret energy expenditure, including energy for running, digging, investigating burrows, and thermoregulation. From field data, we estimate that ferrets expended an average of 130 kcal day −1 during winter. We used the Siberian polecat M. eversmanni as a biological model for the endangered ferret to estimate energy and nutrient aquisition from two ferret prey species. Gross energy content, proximate analyses and utilisation by the polecats of the two prey did not differ and were comparable to results for other carnivores. The polecats consumed an average of 125 kcal day −1 during trials, which is equivalent to 104 metabolisable kcal day −1. At least 20 prairie dogs must be eaten by a ferret during the four winter months (December–March) to meet these requirements. During summer months lactating female ferrets might need to eat prairie dogs at up six times this rate. Our results have conservation implications, including expected ferret densities in prairie dog towns.