HABITAT USE BY BLACK-TAILEDDEER IN RELATION TO RATE OF FORAGE INTAKE

Abstract

Availability of digestible energy is potentially the most important limiting factor of black-tailed deer (Odocoileus hemionus sitkensis) from a nutritional perspective, but patch use by other ruminants has been netter correlated with intake rates of digestible protein and digestible dry matter. We hypothesized that black-tailed deer would concentrate their use in habitats in which intake rates of digestible energy or protein were highest. Using direct observations of 9 tractable deer over a continuous 2-year period, we examined animal-specific rates of: (1) dry matter intake; (2) protein intake; and (3) metabolizable energy intake in 4 habitats. Those habitats were Vaccinium, devil's club (Oplopanax), skunk cabbage (Lysichiton), and beach. For each animal, we compared the observed time spent active in each habitat to predictions of time allocation based on the measured rates of intake. Intake rates in summer differed significantly for all animals among habitats. In the first summer, animals used habitats on the basis of habitat availability and not relative to intake rates obtained in each habitat; the second summer deer used habitats in proportion to digestible dry matter and intake rates of metabolizable energy. In winter, when intake rates varied significantly among habitats, deer used habitats in proportion to their availability. Habitat use cannot be predicted by intake rates in winter. When we compared actual habitat use by black-tailed deer with use predicted by observed pellet defecation, we concluded that pellet groups did not accurately predict habitat use by black-tailed deer in spring, summer, or on an annual basis in the fine-grained habitats of our study area.