Movement Mondays

Maggie MacPherson: Jan 26th 

How does disease vs. abiotic factors shape the evolution of migratory phenotypes? Explaining the loss of migration in American Robins

Trent University

Summary: Seasonal migrations are annual geographic range shifts essential for reproduction and survival but have widely begun shifting or stopping under global (climate and land use) change. Partial migrant populations are ideal for distinguishing the environmental factors determining movement phenotypes because sister populations have high environmental and genetic overlap. American Robins (Turdus migratorius; AMRO) are uniquely suited to this work because they are highly susceptible to disease (West Nile Virus; WNV, a biotic factor) and live along latitudinal gradients with varying degrees of temperature, precipitation, and land change. I am using the phenomenon of partial migration (where some individuals migrate and others do not) to quantify the causes and consequences of migratory vs. sedentary behaviour in AMRO. Work in west-central Illinois demonstrated that more than half of all AMRO had antibodies for WNV, indicating that they had developed a recent immunity. AMRO were more abundant in urban compared to rural habitats, but we found no difference between habitats in the proportion of individuals with WNV antibodies. We did find a trend that more birds had WNV antibodies during migration seasons compared to the breeding season. Next, we will track individuals from across a latitudinal gradient from northern Manitoba to central Illinois to test how abiotic (temperature, precipitation, snow depth, etc.) and biotic (e.g., disease) factors are managed by migratory and sedentary individuals to maximize reproduction or survival. Escaping from disease is thought to drive short-distance shifts in range boundaries, but it remains that we do not understand how disease impacts migration behaviour.