Experience does not change the importance of wind support for migratory route selection by a soaring bird

Abstract

Migration is a complex behavior that is costly in terms of time, energy, and risk of mortality. Thermal soaring birds rely on airflow, specifically wind support and uplift, to offset their energetic costs of flight. Their migratory routes are a record of movement decisions to negotiate the atmospheric environment and achieve efficiency. Because thermal soaring is a complex flight type that young birds need to learn, we expected that, as individuals gain more experience, their movement decisions will also increasingly favor the best thermal uplift conditions. We quantified how route choice during autumn migration of young European honey buzzards (Pernis apivorus) was adjusted to wind support and uplift over up to four years of migration and compared this to the choices of adult birds. We found that wind support was important in all migrations. However, we did not find an increase in the use of thermal uplifts, which could be an artifact of the uplift proxies that we used. Age-specific variations in response to airflow might occur at a smaller spatio-temporal scale than we investigated.