November 18, 2013
U.S.

Wind energy turbines kill hundreds of thousands of bats

Rick Docksai | Science Recorder | Monday, November 18, 2013 | www.sciencerecorder.com

Birds aren’t the only wildlife potentially imperiled by wind energy turbines. The blades kill large numbers of bats, too. A paper published Friday in Bioscience counted more than 600,000 bat deaths caused by wind turbines in the United States last year.

And that is just a conservative estimate, according to the paper’s author, biologist Mark Hayes of the University of Colorado, who said that last year’s death toll could run as high as 900,000. He identified the Appalachian Mountains as the region with the highest concentration of kills.

Hayes derived his estimates from tallying up the dead bats from 21 wind turbine locations and projecting for the full
number of wind turbine locations across the country. The bats die in two ways, he explained: by direct collisions with the blades, or by air pressure fluctuations that the blades create and which bats run into when they are in the blades’ vicinity. The latter, which is the bigger danger, causes a lethal “barotrauma” effect—i.e., the bats pop from the inside, somewhat like human SCUBA divers who suffer excruciatingly painful and sometimes deadly “bends” when they emerge from deep underwater too quickly.

Numerous studies have found similar wind-turbine-related fatalities for birds. For instance, a study published this year in the Wildlife Society Bulletin estimated that 573,000 birds were killed by wind turbines. Another study, published this year in the Journal of Raptor Research, reported U.S. Fish and Wildlife Service estimates of 67 golden and bald eagles killed by wind turbines over the last five years. All of these numbers fall short of even Hayes’ conservative estimates for bat deaths, however, so the bats appear to be even more susceptible.

And the last few decades have been hard on the bats as is. Biologists report that bat populations are decreasing, possibly due to climate change and the spread of diseases such as white-nose syndrome. Bats are more vulnerable to these stressors than many other species, the biologists note, because the average female bat doesn’t bear more than one new pup a year, and the mortality rate is high.

Bats are one of the largest consumers of insects in some parts of the country, so their depleted numbers may have the effect of increased insect swarms. This will be troublesome for farmers, who already spend billions of dollars a year on products and services to suppress crop-killing insects and will likely have to spend even more with fewer bats around to help keep the bugs in check.