Habitat Selection and Survival of Mule Deer: Tradeoffs Associated with Migration

We examined tradeoffs related to migration in a population of mule deer (Odocoileus hemionus) in southern California from 1989 to 1991. All male deer that we radiocollared were migratory, whereas females exhibited a mixed strategy with both migrant and resident individuals. Increased movements of deer were associated with decreased temperatures and increased weekly precipitation. No differences within seasons in the sizes of home ranges occurred for either migrant or resident deer. The size of home ranges of deer, however, was smaller in summer than in winter. Sizes of home ranges were associated positively with proximity to human development and to the amount of avoided (use was less than availability) habitat in the home range. Deer avoided human developments in all seasons. Further, males and resident females used areas farther from water in summer than expected by chance, whereas migratory females selected areas nearer to water. In summer, migratory females selected meadows, riparian habitats, and pine forests, whereas resident females avoided riparian habitats and used pine forests less than did migratory females. Migratory males used habitats in a way similar to migratory females, although they avoided meadows and riparian areas. Clear tradeoffs existed for deer in montane southern California about whether they migrated. Migratory females were farther from human disturbance and used habitats of high quality more often than did nonmigratory conspecifics. Nonetheless, deer were at increased risk of predation during migration and, in years of low precipitation (low snow), had higher rates of mortality than did resident deer. Thus, in areas with extremely variable precipitation and snow cover, a mixed strategy for migration can be maintained in populations of mule deer.