Before the construction of wind turbines, instances of bats colliding with these man-made structures were rarely seen. However, hundreds of thousands are now killed annually, with most found dead beneath the turbines in late summer and fall.
Scientists with the US Geological Survey (USGS) found that tree bats, such as the hoary bat (Lasiurus cinereus), were the most likely to confuse wind turbines for tall trees.
"If we can understand why bats approach wind turbines, we may be able to turn them away," lead author and USGS research biologist Paul Cryan said in a statement. "Advances in technology helped us overcome the difficulties of watching small bats flying in the dark around the 40-story heights of wind turbines. The new behaviors we saw are useful clues in the quest to know how bats perceive wind turbines and why they approach them."
Cryan and his colleagues used thermal and infra-red video surveillance to observe bat behavior around three wind turbines over three months, according to the study, published in the journal Proceedings of the National Academy of Sciences.
The footage showed that over 900 times bats tended to approach the wind turbines closely, and mostly from downwind and when the wind speed was lower. Researchers believe that the nocturnal animals are mistaking the turbines' seemingly familiar wind flow patterns for those they would normally encounter around a tall tree.
"They don't have anything in their evolutionary history that would prepare them for something that looks and feels like a tree but isn't a tree," Cryan told ABC Science.
Bats, the researchers speculate, are accidentally caught in the line of fire when they are unable to dodge the blades or they are moving faster than the bats perceive.
The authors hope to use this information to help reduce wind turbine-related bat fatalities.
"It might be possible to efficiently further reduce fatalities with this method by accounting for sporadic gusts of wind during low-wind periods when bats might be hanging around turbines," said author Cris Hein.