COS 184-4 - What drives migration timing and overwintering in a partially migratory Alaskan caribou herd?

Abstract: Migration is common across the globe, yet shows great variability in distance, duration, route fidelity, and the proportion of the population that migrates. We examined migration and overwintering dynamics in the Teshekpuk Caribou Herd in northwestern Alaska, which displays a variety of migratory behaviors. Most of the herd overwinters within the summer range on the tundra of the northern coastal plain, while other individuals migrate hundreds of kilometers to spend the winter in foothills and mountains. We identified four distinct wintering areas, with multiple areas used by the herd each year. Previous work showed that individuals vary from year to year in which wintering area they use, with a relatively low probability of reusing the same wintering area in subsequent years. GPS collar data from 192 adult female caribou (Rangifer tarandus) between 2004-2021 were used to identify drivers of migration behavior and wintering area use. We examined the influences of population size, animal age, and parturition status, as well as environmental conditions including vegetation productivity, weather variables, insect harassment, and broad-scale climate indices. Influences of covariates were investigated at multiple scales to determine what scale of factors influences animal movement behavior. Preliminary results indicated that selection of overwintering areas was influenced strongly by metrics associated with the individual’s condition (age, parturition status, population size) as well as by summertime forage availability. Migration timing, on the other hand, was not strongly influenced by intrinsic conditions, but responded more to weather, forage, and overwinter destination. The Arctic is undergoing rapid climate change as well as experiencing increasing human activity and development. Better understanding the patterns of space use by arctic ungulates and drivers of those patterns can help suggest solutions to minimize potential conflicts. Our findings improve understanding of the patterns and drivers of migration behavior for a species with broad ecological importance and great cultural and subsistence value to the people of northwestern Alaska.