Movement and migration ecology of Alaskan golden eagles

Abstract

Golden eagles Aquila chrysaetos are distributed across the Holarctic; however, in Alaska and other northern areas, many are long-distance migrants. Being soaring birds, golden eagles can use weather and features of the energy landscape to offset the energetic costs of movement and migration. In this dissertation, I investigate how dynamic energy landscapes, in addition to other habitat and anthropogenic features, affect the movement and migration ecology of Alaskan golden eagles; in most cases I did such by developing and applying new, biologically-appropriate statistical methods. First, I identified a single, discrete navigation decision that each eagle made during migration and determined which weather variables are primary factors in driving that decision. I found that wind was the primary correlate to the decision, consistent with eagles likely avoiding poor migration conditions and choosing routes based on favorable wind conditions. Second, I investigated how different forms of flight subsidies, which were orographic uplift, thermal uplift, and wind support, drove behavioral budgets and migratory pacing of eagles. I found a consistent daily rhythm in eagle behavior and migratory pace, seemingly driven by daily development of thermal uplift, with extended periods of slower-paced movements, consistent with periods of opportunistic foraging. Third, I investigated the effects of anthropogenic linear features, such as roads and railroads, on eagle movement during migration. I found that eagles selected for roads during spring migration and were more likely to be near roads when making slower-paced movements, which would be most frequent during times when limited thermal uplift is available. Lastly, I compared how floaters (breeding-age, non-territorial individuals) and territorial eagles used space and selected for resources, specifically interested in how their movements and space use might overlap. I found that floater space use was much more expansive, yet they only selected for habitats and resources slightly differently than territorial eagles. I also found their home ranges overlap substantially, suggesting that floaters play a key role in the population ecology of migratory golden eagles in Alaska.