Migration is common across the globe, yet partial migration, in which only a subset of a population migrates between seasonal ranges, has only recently been recognized to occur across a diverse range of species. A better understanding of the variability of behaviors shown by partially migratory species, as well as the factors that influence this variability over time, will improve knowledge of animal movement ecology. We examined migration dynamics in the Teshekpuk Caribou Herd (TCH), which displays a variety of migratory behaviors. Most of the herd remains within the summer range on the northern coastal plain of Alaska, while other individuals migrate hundreds of kilometers to overwinter in the foothills and mountains of the Brooks Range. Migration behavior and timing was identified using First-Passage Time and Net-Squared Displacement. We used these classifications to ask how the probability of using coastal plain versus mountain winter areas, as well as patterns of migration timing and duration, were influenced by both intrinsic (e.g., age, parturition status) and extrinsic (e.g., vegetation productivity, snow depth and timing, temperature) factors.
Results/Conclusions
GPS collar data from 79 female caribou between 2004-2016 were analyzed using mixed effect models. Individuals had between 1-8 years of locations, resulting in 173 caribou-years of observations. Migratory behavior was common among collared caribou, averaging 76% in the spring and 84% in the fall. While the proportion of migrants varied, it did not do so in a consistent direction over time. Similarly, there was variability in the proportion of migrants overwintering in the mountainous areas (mean = 0.37, range = 0.06 – 0.77). Spring movements featured more linear, directed movements than were recorded in fall (spring mean directedness = 0.63, fall = 0.44, p < 0.001), suggesting the likely role of a biological imperative spurred by the need to reach calving grounds in the spring. Further investigation of the influence of extrinsic covariates is needed. The Arctic is undergoing some of the fastest levels of climate change as well as experiencing increasing human activity and land use. Our findings provide the opportunity to explore how migration behavior responds to rapidly changing environments in far northern landscapes and have implications for wildlife management of a key species for subsistence hunters.