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Windmills: 600,000, Bats: 0. Time for a New Game?

A new study estimates that at least 600,000 bats died last year in the Lower 48 from wind turbines.


A lot of bats are exploding in the United States, and it’s because of renewable energy.

A new study published in the journal BioScience estimates that more than 600,000 bats died from interactions with wind turbines in the continental United States last year alone. Given the various issues bats have had with deadly white-nose syndrome, climate change, and that they generally only give birth to a single bat pup a year, this is a worry. How much of a worry is unknown, writes author Mark A. Hayes, a bat biologist at the University of Colorado-Denver: Since their subjects are small and nocturnal, researchers don’t have a good handle on how many bats are in the U.S.

Even if the population was known definitely, Hayes says his estimate of deaths—based on fairly elaborate “distribution-fitting analysis”—is almost surely on the low side, perhaps only two-thirds the real figure. (His figures are in the ballpark with earlier wind vs. bat studies using other forms of estimation.) Hayes used the lowest numbers whenever a range of deaths was presented from the 21 locations across the nation he studied. Most of the other work he drew those numbers from only looked at bat fatalities during peak migration times, when figures were likely to be at the highest but which also misses the drumbeat of bat deaths from the rest of the year. Some of the areas with the largest known populations of bats, like the Southwest, didn't have study sites.

Besides the core idea that it’s a bad idea to remove any species from the linked chain of life, bats in particular eat a lot of bugs, including mosquitoes, that cause problems for farmers and suburbanites.

Meanwhile, expect a lot more windmills. Wind energy is an increasingly popular power source in the United States, with 2012 the best year on record for installed capacity and the largest source of new electricity that went on line last year. America’s cumulative installed wind energy capacity is 2,200 percent since the year 2000 (from an admittedly small base) and reasonable expectationsespecially now that power from wind is relatively cheap—are that one fifth of the nation’s electricity will come from wind before 2030.

Interestingly, beyond just estimating total deaths, Hayes compared electrical generation capacity to bat mortality, although he didn't explicitly state that the two were correlated. He also didn't compare mortality based on turbine design—they vary widely—which seems like fertile ground for investigation. And while he didn't generate regional estimates, Hayes shows that the greatest carnage per megawatt occurred in the Appalachians. While the bat carcasses are a fact, whether Tennessee and West Virginia wind turbines are somehow more deadly, or that their toll reflects poor data from other windy-and-batty areas, is an open question.

Given that wind turbines are basically a collection of whirring blades, you might assume that the bats found dead have been sliced and diced. You might also wonder how an animal that uses radar to find a single mosquito in the dark could fail to sense a monstrous wind turbine. The University of Calgary’s Erin Baerwald explained this to Discovery News in 2008: "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.' Bats can detect and avoid all kinds of structures," and are even better at detecting stuff that’s moving. No, they're exploding. As I learned  last year, “Baerwald and her colleagues discovered that bats' ‘large, pliable lungs’ blow up from change in air pressure created by moving blades. Up the 90 percent of the dead bats they examined showed the internal bleeding consistent with their argument. Birds, by the way, have different kinds of lungs so their deaths are from the more predictable blunt-force trauma.”

If you’re not the kind of person who isn’t automatically appalled by the destruction of small, furry creatures, why would you care about bats? Besides the core idea that it’s a bad idea to remove any species from the linked chain of life, bats in particular eat a lot of bugs, including mosquitoes, that cause problems for farmers and suburbanites. They also pollinate some plants.

Despite being a bat guy, Hayes doesn’t call for muzzling wind power. For that, leave it to the bird partisans (or are they anti-wind partisans?). Bird strikes are a concern, and while it now looks like more bats than birds are victims, the loss of highly charismatic eagles turns more heads than the loss of even lots more frankly creepy-looking bats. Nonetheless, bird protectors and wind fans in some cases have found a modus vivendi. Now it’s time for bats and their human friends to step up to the plate, with the hope we can have more whiffs and fewer strikes.