Song flight and 3D thermal detection provide evidence for bat attraction to wind turbines in Central Europe

Fatal interactions with wind turbines are a major threat to bat populations worldwide. Yet, the ultimate causes for bats colliding with wind turbines remain elusive. Using an extensive acoustic data set recorded at nacelle height in different parts of Germany, we show that feeding and social activity occur at all studied wind turbines. At least seven bat species (accounting for 95% of German bat fatalities) perform song flight at wind turbines, a behavior related to mating and courtship, indicating that males may find wind turbines attractive for establishing mating territories. Male songs broadcast over considerable distances and could function as acoustic beacons attracting females to turbine sites. Analysis of 3D thermal detection shows that bat density is higher in the rotor swept zone than in the free air space surrounding turbines. This strongly suggests that bats actively approach turbines, possibly in search of mating, roosting and/or foraging opportunities.