The explanation to this puzzle is that the bats' lungs effectively blow up from the rapid pressure drop that occurs as air flows over the turbine blades.
"The idea had kind of been floating around, because people had noticed these bats with no injuries," said Erin Baerwald of the University of Calgary and lead author of a study about the finding in the journal Current Biology.
Researchers examined a large sample size of hoary and silver-haired bats found under wind turbines, performing necropsies on the bats within hours of their death.
The damage from rapidly expanding air in the lungs caused by the sudden drop in pressure was clear. Ninety percent of the bat deaths at the southern Alberta site involved internal hemorrhaging consistent with such damage, called barotrauma, while only 50 percent showed signs of collision with turbine blades.
For those overlapping cases, it may be that the bats flew through the pressure drop, suffered barotrauma, and then were struck by a blade. It is also possible that they were struck first, causing internal hemorrhaging.
But, Baerwald said, "When people were first starting to talk about the issue, it was 'bats running into the turbine blades.' We always said, 'No, bats don't run into things.' Bat's can detect and avoid all kinds of structures."
In fact, they are even better at detecting moving objects, Baerwald said.
"This kind of answers that mystery," she added. "It was something nobody could have predicted."
The bat fatalities appear to be a more significant problem than bird deaths from wind turbines in most locations. "Here we're picking up ten bats for every bird," Baerwald said.
"I can pick up nine different species of bird. I can pick up two species of bat," she added. "The impact on the populations is very different."
Whether these deaths are having a significant effect on the bat populations in Alberta or elsewhere is difficult to gauge because so little is known about the bats.
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