Ever-courteous and vulnerable bats

Controversial wind farm in Tucker County, West Virginia

Bats are in the news twice this week for two very different reasons: more has been revealed about their endearing social graces, and more is now understood about their unique vulnerability to windmills.

University of Maryland researchers announce in this week’s issue of the Proceedings of the National Academy of Sciences that big brown bats keep quiet when hunting with others to avoid jamming their companions’ sonar.

If they’re hunting solo, the bats echolocate using their own vocalizations about 99 percent of the time. But when they’re flying near others, they’re quiet 76 percent of the time, switching from active to passive echolocation. Past research had already found that echolocaters sometimes switch frequencies to avoid interfering with each other–but this is the first research to show they go mum altogether.

If only humans were always so thoughtful!

The other news is not so good for bats. It turns out their amazing echolocation abilities aren’t enough to save them from death by windmills. Bats’ sonar indeed detects the windmills before they collide with them, which would theoretically give them an advantage over birds. But a team of researchers at Canada’s University of Calgary report this week that bats don’t have to collide with a windmill to die. Their findings appear in the journal Current Biology.

The researchers examined bats that had died at windmill sites, and found 90 percent of them died because of a sudden atmospheric pressure drop near the blade. The pressure drop caused their balloon-like lungs to expand, leading to internal hemorrhaging and death.

The study found that most of the bats killed at wind turbines are migratory bats that roost in trees, including hoary bats, eastern red bats, and silver-haired bats. Those species are often secretive, so not much is known about their populations. But researchers do know that such bats are long-lived and reproduce slowly–so any hits to their numbers could have noticeable and long-term consequences.

National Public Radio did a nice job of reporting on controversial windmills in Tucker County, West Virginia, pictured above. That 2006 story is available here.

A summary of the quiet bat story is available here, with an option to buy the whole paper.

A summary of the study about bats and wind turbines is here, with the same terms.