Wind turbines may be killing bats without touching them: A new study suggests that the localized drop in air pressure caused by the whirling blades is causing the delicate lungs of bats to burst. While environmentalists previously worried about birds getting slashed by the turbines' blades, researchers realized a year ago that bats are more at risk from the the turbines.

In May 2007, the US National Research Council published the results of a survey of US wind farms showing that two bat species accounted for 60% of winged animals killed [New Scientist].

But until now, the bats' mode of death was unknown. Because bats navigate using a sophisticated echolocation system, researchers thought it was unlikely that the bats were getting caught in the turbines. Says lead researcher Erin Baerwald:

"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" [Discovery News].

When outside pressure drops, the bats' air sac over-expands, bursting the capillaries around it. Their lungs fill with blood and fluid - similar to drowing [sic], the researchers said [Calgary Herald].

Bats are particularly susceptible to the condition, called barotrauma, because they have balloon-like, expandable lungs.

Bird lungs are more rigid and tube-like and better able to withstand sudden changes in air pressure [CBC News].

The study, published in the journal Current Biology [subscription required], was conducted at a windfarm in Alberta, Canada, over the course of two years. The species of bats found dead on the ground beneath the turbines were primarily three migratory species: hoary bats, eastern red bats, and silver-hair bats. The researchers found that 90 percent of the dead bats had internal hemorrhaging which matched the symptoms of barotrauma, while only 8 percent had external injuries and no internal bleeding.

Image: flickr/Zeusandhera