From thermal to flyway: how weather shapes the soaring migration of European Honey Buzzards Pernis apivorus at multiple scales

Billions of birds migrate across entire continents each year. Yet we know very little about how weather conditions shape the epic journeys of long-distance migrants. In this dissertation, Wouter Vansteelant combines classic field observations and cutting-edge animal tracking technology in order to unravel how European Honey Buzzards Pernis apivorus negotiate the weather from thermal to flyway. Migrating birds are often thought to maximize their migration speed when adjusting flight behaviour to variable weather conditions. However, Honey Buzzards seem to compromise between time-optimal and risk-averse strategies across multiple scales of migratory movement, ranging from the speed at which they glide between thermals to the migration routes they choose during each season. The birds effectively allow themselves to be pushed by the weather during most of their journeys, travelling along detours in anticipation of large-scale wind regimes between Europe and Africa. Weather conditions thus greatly affect the routes and timing of individual migrants. However, by going-with-the-flow Honey Buzzards avoid the risk of exhausting their energy reserves along the way, and they manage to arrive on time to breed almost every year.