Habitat Quality Influences Migratory Strategy of Female White-Tailed Deer
Partial migration is a life history strategy that is common for ungulate species living in seasonal environments. One factor that influences the decision to migrate by ungulates is access to high quality habitat. We evaluated the influence of access to winter habitat of high quality on the probability of an individual migrating, the differences in seasonal habitat use between and within migratory and resident classes of deer, and the effects of this decision on the survival of female white-tailed deer. We hypothesized that deer with home ranges of relatively low quality in winter would have a relatively high probability of migrating, the quality of home range in summer would be approximately equal as migrants moved to relatively higher quality home ranges, survival of migrants in winter would be lower than residents due to home ranges of lower quality, and survival would be comparable in summer between migrants and residents. We radio-collared 67 female white-tailed deer (Odocoileus virginianus) in 2012 and 2013 at 7 capture sites within the study area. The odds of being a migrant increased by 3.1 per 1-unit increase in home range size and decreased by 0.29 per 1-unit increase in the proportion of cropland within home range in winter. The habitat with the highest probability of use in winter for residents was pasture (1.00, SD = 0.01) and for migrants was riparian (0.73, SD = 0.39). In summer both groups had the highest probability of using pasture (resident = 0.96, SD = 0.15; migrant = 0.99, SD = 0.08). We integrated the migration probability and survival models to estimate annual and seasonal survival rates of migrants and residents. We found little difference between the annual and seasonal rates of survival. Annual survival rates for migrants and residents were 0.87 (SD = 0.06) and 0.83 (SD = 0.07), respectively. Our results indicate that access to habitat of high quality may be a strong influence on a female white-tailed deer’s decision to migrate. We suggest the presence of partial migration in a population may be a response to competition for high quality habitat.