Assessing Drivers of Partial Migration in Elk

MS Thesis, Kristin Barker

In recent decades, researchers worldwide have noted changes in migratory behavior of ungulates, often in response to changing climate or land use practices (Berger 2004, Bolger et al. 2008). Adaptation of a migratory species to changing external conditions relies in part on the primary drivers of its migratory behavior, but these drivers can be difficult to discern across the range of conditions experienced by a species (Shaw 2016). Across the state of Montana, elk (Cervus canadensis) populations range from being almost completely resident to almost completely migratory, and some populations display behaviors that span a continuum from residency to migration. Although the influence of nutritional resources on migratory behavior of ungulates is fairly well-understood, relative influences of other factors that may drive individual variation in migratory behaviors remain less clear. We are using GPS collar data from 312 elk in 16 herds to investigate how forage variability, conspecific density, animal age, and human disturbance affect the likelihood that an adult female elk will migrate or exhibit intermediate behavior rather than remain resident on winter range. Identifying the factors that most strongly influence migratory behavior will provide a comparative assessment of several hypotheses currently posited to explain partial migration in ungulates, while simultaneously helping managers identify potential means of manipulating behaviors to meet management objectives.