Sexual Dimorphism and Energy Expenditure for Reproduction in Female Fisher Martes pennanti

We develop a model for the energy expenditure of a lactating female fisher. The model includes energy expenditure for maintenance, hunting, prey capture, lactation, climbing, and thermoregulation. Using radio telemetry, we followed the activities of a female fisher with kits in Manitoba, Canada and applied our model to this animal. These are the first estimates of energy expenditure and energy requirements of a free-living female mustelid during lactation. When the kits were small, the female spent as much as 21 h per d away from them hunting, travelling over 13 km, and expended as much as 2285 kJ. Our estimates of energy expenditure for a female fisher during lactation support the hypothesis that sexual dimorphism in body size is related to energy budgets in the Mustelidae.