The hypothesis that forage intake rate in large (i.e., vertebrate) herbivores is a function of plant availability (biomass), bite size, and forage fibrousness was tested with tame Sitka black—tailed deer (Odocoileus hemionus sitkensis). Deer were offered single—species diets of eight commonly consumed plants or plant parts that provided a variety of bite sizes and chemical or structural characteristics. The hypothesis that intake rate is a function of plant availability was tested by varying the density of plants offered on an artificial "pasture" and measuring consumption rates. Intake rate was independent of plant availability, except for plants of small bite size at densities <0.5 g/m2. Intake rate was highly correlated with bite size and plant fibrousness, measured as neutral detergent fiber concentration. We conclude that intake rate is a direct function of processing constraints (chewing) imposed by plant tissues on the herbivore. Bite size indirectly affects intake rate because as bite size declines, the animal attempts to compensate by increasing bite rate. Since cropping directly competes with chewing, intake rate declines. Because bite size and fibrousness of plant tissues affect foraging time, foraging selection by large herbivores may be significantly affected.
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Spalinger et al. (1988) studied this question.