Bats have no natural defense against the unnaturally dramatic pressure changes.
"Bats can actually detect pressure changes, but we're talking large-scale, relatively slow changes, like the coming of a storm front," said Baerwald. "This is something entirely different."
Most bats that fall victim to turbines are migrating species, such as hoary bats, eastern red bats, and silver-haired bats.
There are not enough data to determine how wind turbine fatalities might be affecting populations of these slow-reproducing mammals.
Birds are also killed by blows from wind turbine rotors (see a related story), but their rigid, tubelike lungs can better withstand air pressure changes.
The study appears this week in the journal Current Biology.
Curiosity Killed the Bat
"They are the first to have done a large scale look at this barotrauma," Bat Conservation International (BCI) biologist Ed Arnett said of the researchers.
"It's fascinating information," said Arnett, who is not involved with the study.
"But ultimately it might not matter so much how [the bats] die but what is attracting them to the turbines in the first place."
Preventing the bat deaths has challenged experts for years.
"We've partnered with industry and federal agencies to raise and spend about two million dollars looking for a solution," said BCI founder and president Merlin Tuttle.
Laurie Jodziewicz, of the American Wind Energy Association in Washington, D.C., said where the turbines are placed may be the key.
"Bats are not being [killed] at all the wind projects all over the country—it is happening in some places and not others," she said.
"We're trying to determine before construction what areas might be risky."
Turbines create drops in pressure drop during normal operations, so the problem could possibly be addressed by changing when the turbines run, according to BCI's Tuttle.
"A large portion of the kills occur at the lowest wind speeds," he said, "and at those low speeds [the turbines] are not generating appreciable electricity anyway."
Bats also are at particular risk during migration periods in late summer and early fall, when many turbine related fatalities occur.
Arnett, Baerwald, and others are currently conducting tests to see if raising the "cut-in" wind speed at which rotors begin to turn will save bats—particularly during peak migration periods.
"It won't eliminate the problem, but it's a good step in the right direction," Tuttle said.
NOTE: About 90 percent of the bats studied suffered from barotrauma. The name of the ailment was restored to this article for clarification purposes after initial publication.
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