An unprecedented number of bats are being killed by wind turbine blades. A new report has found bats may be mistaking wind turbines for trees.
Bats are often looking for a place to roost when the moon is bright and winds are low. That’s when the conditions can be the deadliest for bats flying near wind turbines.
Researchers used infrared video to track movements at a wind farm in Indiana. They saw bats repeatedly approaching the turbines when the blades were moving slower than when they were moving faster.
Paul Cryan, research biologist with the U.S. Geological Survey, said this study helps people know more about bat behavior.
“The majority of bats we see flying near the turbines in this video alter course and go check out the turbine in some way,” Cryan said.
Cryan said bats probably approach turbines by flying against the wind because that is they way they approach trees. researchers aren’t sure what the bats are looking for. He said it could be a place to rest during migration, insects, or to socialize with other bats.
Cryan said migrating tree bats most often die at wind farms in the late summer and fall months.
The hoary and silver-haired bats most often die at wind farms in the Northwest, said Cris Hein, with Bat Conservation International. Hein is also a co-author on the study.
“Once we found out that bats were an issue with respect to wind energy, which was a little over a decade ago in 2003, we’ve been trying to find ways to reduce fatalities and not have that much of an economic impact on the industry,” Hein said.
Hein said over that time hundreds of thousands of bats have died at wind farms.
Wind industry advocates say they are working to prevent bat deaths. John Anderson, director of permitting policy and environmental affairs at the American Wind Energy Association, said many wind developers follow voluntary guidelines from the U.S. Fish and Wildlife Service.
“These guidelines represent the most robust voluntary approach for minimizing development impacts for any energy industry (or other land use) that we are aware of,” Anderson said.
He said this study confirmed ideas about bat behavior that have been understood for several years.
“Where the studies are helpful is in helping the industry, conservation community, and regulators to better understand bat behavior around turbines, what actually creates risk and when that risk is greatest, and therefore when and where to apply mitigation measures,” Anderson said.
Researcher Cryan said this study could also help with other deterrent technology, like high-pitched frequencies that might drive bats away, or monitoring devices that would know when endangered bats are flying nearby. Cryan said it would be best to aim the devices toward the back of the turbine, where the video evidence shows bats approaching.
Researchers in Canada and the U.S. found that when they only let the turbines spin on windier days, the bat deaths dropped by 50 percent.