Wildlife

Bats vs. Turbines

A new study estimates that more than 600,000 bats are killed each year by the rotation of wind turbines in the continental United States.

Wildlife experts say those deaths are in addition to the large numbers of the flying mammals that are being killed by white-nose syndrome, which is caused by a fungus that has spread rapidly to bat caves and mines across North America.

Writing in the journal BioScience, University of Colorado researcher Mark Hays notes that the actual number of bat deaths from the turbines could be much higher than the conservative estimate of 600,000.

The majority of bat species produce only one young per year, meaning that their populations are slow to recover.

Most bats don’t die from actual contact with the turbines since their sonar allows them to avoid the blades.

But subtle changes in barometric pressure created by the rotating blades cause the bats’ capillaries to burst, resulting in deadly internal hemorrhaging.

Birds’ circulatory systems are different from that of bats, keeping them from being victims of such “barotrauma.”

Most bat deaths occur when winds are relatively light because bats can’t fly in high winds. And since most turbines shut down when winds go below about 9 mph anyway, experts say increasing the “cut-in speed” to 11 mph would reduce bat deaths by at least 44 percent.

As much as 93 percent of bat fatalities due to turbine barotrauma could be avoided if the cut-in speed was lifted to 15.6 mph, experts say.