Food Intake and Foraging Energetics of Elk and Mule Deer

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Abstract
The energetic cost of grazing was measured using indirect calorimetry with a tracheotomized elk (C. elaphus nelsoni). The cost of eating herbaceous forage averaged 0.32 kcal/kg body weight/h, an energetic increment of 26% over standing costs. Forage intake was quantified using esophageal fistulated elk and mule deer (O. hemionus hemionus). Dry matter consumption rate and mean bite size increased curvilinearly as functions of forage biomass for both species. Asymptotic grass intake rates were 2.22 and 14.04 g dry matter/minute for deer and elk, respectively. Consumption rate and bite size were greater in shrub-forb communities than on grass pastures of comparable biomass. Biting rate ranged from about 15-60 bites/min and was inversely related to bite site. Rate of travel during foraging decreased exponentially with increasing forage availability. A computer model was constructed to evaluate the interaction of time and energy constraints on foraging ungulates. The effects of variation in forage quality, forage abundance and snow cover on the ability of animals to meet daily energy requirements are discussed.