Food Intake and Foraging Energetics of Elk and Mule Deer

The energetic cost of grazing was measured using indirect calorimetry with a tracheotomized elk (Cervus elaphus nelsoni). The cost of eating herbaceous forage averaged 0.32 kcal/kg body weight/ hour, an energetic increment of 26% over standing costs. Forage intake was quantified using esophageal fistulated elk and mule deer (Odocoileus 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 to 60 bites/minute and was inversely related to bite size. 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. J. WILDL. MANAGE. 48(4): 1285-1301 Foraging is the dominant activity of free-ranging ungulates. Wild ungulates typically devote 40-60% of each day to finding and consuming food (Craighead et al. 1973; White et al. 1975; Schwartz 1977; Belovsky and Jordan 1978; Collins et al. 1978; Owen-Smith 1979, 1982; Gates 1980; Hanley 1982). The energetic cost of these activities represents an important component of the animal's energy budget (Young 1966, Osuji 1974, Chappel and Hudson 1978). However, in spite of the significance of foraging in the life strategy of wild ungulates, relatively little is known about the energetics of this behavior. The literature is replete with food habits information, but such observations are of limited value without an understanding of the efficiency with which the animal harvests the food resource and extracts energy from its environment. This study was undertaken to quantify the cost-benefit functions of foraging by captive elk and mule deer relative to food availability. Specific objectives were to: (1) determine forage intake rate as a function of the biomass of acceptable food items; (2) determine the relationship of intake rate to mean bite size and biting rate to better understand the behavioral adjustments that regulate energy intake; (3) quantify locomotion rate during foraging relative to food availability; (4) measure the energetic cost of eating as distinct from expenditures for standing and locomotion; and (5) model the effects of variation in forage quality and abundance on the ability of free-ranging cervids to meet daily energy requirements. This project was funded by the U.S. For. Serv. and Washington State Univ. We thank K. L. Parker for support and assistance in data collection and M. A. Reisenauer for the care of experimental animals. L. D. Bryant and J. W. Thomas provided facilities at the U.S. For. Serv. Range and Wildl. Habitat Lab. in La Grande, Oregon. J. Wildl. Manage. 48(4):1984 1285 This content downloaded from 157.55. 39.29 on Tue, 12 Apr 2016 10:03:48 UTC All use subject to http://about.jstor. org/terms 1286 INTAKE AND FORAGING ENERGETICS OF ELK AND DEER * Wickstrom et al. METHODS AND MATERIALS Elk calves and mule deer fawns were bottle-raised and habituated to the experimental protocol. Training included acceptance of gentle restraint with a head halter, manipulation of the esophageal and tracheal cannulae, and transport in a trail-