Wind-associated detours promote seasonal migratory connectivity in a flapping flying long-distance avian migrant

1. It is essential to gain knowledge about the causes and extent of migratory connectivity between stationary periods of migrants to further the understanding of processes affecting populations, and to allow efficient implementation of conservation efforts throughout the annual cycle. Avian migrants likely use optimal routes with respect to mode of locomotion, orientation and migration strategy, influenced by external factors such as wind and topography. In self-powered flapping flying birds any increases in fuel loads are associated with added flight costs. Energy-minimizing migrants are therefore predicted to trade-off extended detours against reduced travel across ecological barriers with no or limited foraging opportunities. 2. Here we quantify the extent of detours taken by different populations of European nightjars Caprimulgus europaeus, to test our predictions that they used routes beneficial according to energetic principles and evaluate the effect of route shape on seasonal mi...