Ecological Energetics and Foraging Strategies of the Fisher (Martes pennanti)

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Abstract
A model is presented for the daily energy budget of free-living solitary mammals and is applied to the fisher. Energy expenditure of mammals is the sum of the energies expended in different activities, the most important of which for carnivores are sleeping, running (hunting) and prey capturing. Energy expenditure for a carnivore in each of these activities is a linear function of the mammal''s weight to a specified power and its running speed. Two fishers were trained to run on a treadmill to determine the values of the equation parameters for this species. The energy available to a fisher from common prey items is presented. Wild fishers were tracked in the snow and were live-trapped, outfitted with radio transmitters and monitored for activity. Inserting time active and inactive and distance run into the energy budget model yields estimates of energy expended during periods of radio contact and estimates of daily energy expenditure. Daily energy expenditure is estimated to be of the same order of magnitude as, but less than, daily energy acquired from kills and scavenges. The energy budget model and field data are used to develop a simple optimal foraging strategy model for the fisher. A fisher''s optimal foraging strategy depends on estimated search times for each prey relative to estimated energy obtained from each prey but does not depend on handling times and handling energy expenditures.