Nutritional ecology of white-tailed deer : effects of gender on foraging behavior and digestive efficiency

Abstract

Differential resource use, habitat partitioning, and sexual segregation have been noted for many ungulate species. However, the mechanisms behind sexual segregation have not been resolved. This study was designed to examine one of three viable hypotheses, the body size hypothesis. This study explored the impact of body size on foraging behavior and digestive efficiency o f white-tailed deer under controlled experimental conditions. A series of three experiments conducted with male and female deer. First, deer were fed handconstructed feeding patches to evaluate ingestive behavior differences when the effects of plant architecture have been removed. Next, deer were fed intact shrub branches to determine the impact of shrub architecture on foraging behavior and intake rates. Finally, metabolism trials were conducted to evaluate digestive efficiency differences. When fed hand-constructed feeding patches, males generally consume all material offered; perhaps trying to maximize diet quantity. Females chewed their food more throughly (13.4 chews/g) than males (8.23 chews/g), but high variability masked any statistical significance (P = 0.44). Foraging behavior of females and males were influenced by leaf size, spines, and stem length. Males removed entire sections of stems more often than females (P < 0.01) and consumed larger bites (0.68 g) than females (0.51 g, P = 0.05). Consequently, males were more influenced by spines. Alternatively, females removed individual leaves and stem tips and were more influenced by stem diameter and shrub compactness. During metabolism trials, diet quality influenced most aspects of foraging behavior and digestive efficiency. Lactating females had faster (P < 0.05) passage rates (10.4 h) than non-lactating females (17.9 h), but not males (14.2 h). Despite differences in body size, lactating females tended to digest forages as well as males and both groups tended to digest forages better than non-lactating females. The results of this study uphold the basic theories of the body size hypothesis, but suggest that digestive strategy differences due to body size may be far too subtle to explain differences in resource utilization patterns at the bite level of the foraging hierarchy. Additional research is needed to determine if body size differences impact other levels of the foraging hierarchy.