WASHINGTON — It’s not that researcher Paul Cryan set out to prove the old saying, “blind as a bat.” It just seems that way.
For two months, Cryan, a research scientist for the U.S. Geological Survey, led a team that watched the behaviors of migrating tree bats near wind turbines. They set up thermal video surveillance cameras to study them night after night in an attempt to discern why up to 900,000 bats are killed by windmills each year.
In the end, they came away with a simple conclusion. Vision-challenged migrating bats seem to think wind turbines are 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 Marcos Gorresen, a scientist at the University of Hawaii and a co-author for the recently released study.
Long-distance migrating bats, such as the hoary bat, tend to socialize and roost in trees, as opposed to hibernating bats that fly short distances to group in caves. For migrating bats, it seemed to hardly matter that wind from the turbines could toss their little bodies. They fearlessly dived toward the spinning blades of three research wind turbines for various reasons.
Twelve lifeless bodies were found near the machines at a wind farm in Benton County, Ind., during the study period between July 29 and Oct. 1 in 2012. The study was published this month in the Proceedings of the National Academy of Sciences.
More dead bats is bad news, particularly at this time of year. Around the end of the month, hibernating bats will start flocking back to caverns where a lethal disease called white-nose syndrome lurks.
The disease will almost certainly kill tens of thousands of them, as it has every year since it was first detected in New York in 2006. The disease has claimed at least 7 million bats, wiping out about 90 percent of bats in the Northeast, according to a U.S. Fish and Wildlife Service estimate two years ago, and has spread to 25 states and several Canadian provinces.
Financial consequence
The one-two punch of wind turbines and white-nose syndrome is an ecological disaster that hits farmers in the wallet, Cryan said, the study’s lead author. Bats that eat bugs by the metric ton are worth about $3 billion a year in pest control for U.S. agriculture, according to a separate report that Cryan also helped write in 2011.
“People often ask why we should care about bats,” he said. “Bats are saving us big bucks by gobbling up insects that eat or damage our crops.”
The financial boon to agriculture lowers food costs for Americans and is reason enough to give bats more respect and help, Cryan said.
“If we can understand why bats approach wind turbines, we may be able to turn them away,” he said.
That’s easier said than done. Watching radar during those long, lonely nights, researchers noticed that migrating bats seemed unaware of the threat they faced at a wind farm with 600 turbines.
It didn’t help that a dinner buffet flew alongside them. Radar detected more than 3 million flying things during the observation period, most of them bugs. Of those blips, 1,700 were determined to be flying animals, and 80 percent of those were identified as bats.
They hovered, dived toward the three test turbines, chased other bats toward the blades, things they might do near trees with far less dangerous leaves. “At a fundamental level, tree bats may not be able to discriminate wind turbines from trees,” the study concluded.
Turbines, with their great height and tall, round trunks, can look like trees to the dim-sighted. Earlier studies have shown that bats guided by sonar largely avoid smashing into buildings and skyscrapers, unlike the billions of birds that fly into them each year.
But significantly more bats than birds are killed at wind turbines, according to a University of Colorado study by researcher Mark Hayes published last year.
