Why are wind farms killing so many bats?

A bat (left) flutters near the nacelle of a wind turbine in one of the authors' videos.

Wind turbines mostly get bad press for killing birds, but they might actually have a bigger impact on bats, which appear to be killed in large numbers at wind farms. This might disproportionately affect bat populations because, as the authors of a new paper put it, "Bats are long-lived mammals with low reproductive potential and require high adult survivorship to maintain populations."

A team of researchers decided to find out why bats have so many lethal interactions with the turbines. To do so, they used infrared video cameras that imaged any warm-blooded animals close to the wind farm. They also used radar to follow groups of animals flying around the site, which included flocks of migratory birds. In addition, audio recorders were used to determine which species of bats were present, as well as whether they were hunting. Combined with over 1,300 hours of video footage, the data presented a fairly complete picture of the areas near the wind farm in question.

Eighty percent of the close encounters observed between animal and equipment involved bats. The mammals flew near the blades and the body of the wind turbines, sometimes within two meters. In some cases, they chased each other around the hardware or lingered for several minutes near it. The close approaches were more common under two conditions: the presence of bright moonlight and during periods of low winds. The bats also typically approached from the downwind direction when the wind was slow.