A study recently published in the journal Proceedings of the National Academy of Sciences reveals the reasons why windmills kill up to 900,000 migrating bats each year, in addition to a disease that claims the lives of tens of thousands of bats annually in the northeast United States since its discovery in 2006.

Researchers of the study, led by Paul Cryan of the U.S. Geological Survey, observed the behaviors of migrating tree bats near wind turbines by setting up thermal video surveillance cameras. They concluded that the bats that are vision-challenged can not tell significant differences between wind turbines and trees.

“The way bats approach turbines suggests they follow air currents and use their dim-adapted vision to find and closely investigate tall things shaped like trees,” said co-author Marcos Gorresen, a scientist at the University of Hawaii, according to the Washington Post.

Unfortunately, wind turbines are not the only factor in the deaths of migrating bats this year. The Washington Post also reports that at this time of year, hibernating bats begin traveling back to caverns, where the lethal white-nose syndrome disease can be found.

White-nose syndrome was first detected in New York in 2006, killing tens of thousands of bats each year. According to a U.S. Fish and Wildlife Service estimate two years ago, the disease has killed at least 7 million bats and has spread to 25 states and several provinces in Canada.

“I’m terribly, terribly concerned,” said Katie Gillies, a conservation biologist for Bat Conservation International. “I don’t think the disease will run its course. There is no way to save our bats from white nose without intervention. The situation is . . . absolutely dire.”

Researchers state that the combination of wind turbines and white-nose syndrome destroying the population of migrating bats can be significantly harmful for farmers. According to a separate report by Cryan, written in 2011, bats that eat bugs by the metric ton may be worth approximately $3 billion per year in pest control for U.S. agriculture.

“People often ask why we should care about bats,” said Cryan. “Bats are saving us big bucks by gobbling up insects that eat or damage our crops. If we can understand why bats approach wind turbines, we may be able to turn them away.”