Echolocation activity of migratory bats at a wind energy facility: testing the feeding-attraction hypothesis to explain fatalities

As development of wind energy facilities continues, questions of why fatalities of migrating insectivorous bats occur at turbines still remain. Numerous hypotheses have been proposed, including a feeding-attraction hypothesis that suggests bats may be attracted to insects congregating near turbine nacelles. To test this hypothesis, we analyzed echolocation calls of hoary (Lasiurus cinereus) and silver-haired (Lasionycteris noctivagans) bats recorded over 72 nights at a wind energy facility in Southern Alberta, Canada. We recorded calls at 3 heights: 67 m at turbine nacelles, 30 m at meteorological towers, and ground level at turbines and meteorological towers. We used feeding buzzes as indicators of foraging behavior. We compared the occurrence of feeding buzzes across heights, and between turbines and meteorological towers to test the prediction that if bats are attracted to turbines for foraging, there will be a greater proportion of feeding buzzes at turbines, and in particular, at nacelle height. We found no significant evidence that foraging rates were higher at nacelle height compared to 30 m or ground level, or between turbines and meteorological towers for either species. For silver-haired bats, foraging activity was greater at meteorological towers, and in particular, at 30 m height. These results do not support the feeding-attraction hypothesis for silver-haired or hoary bats, and suggest that while some bats forage in the vicinity of wind turbines, they are not specifically attracted to turbines to feed.