Wind Farms Make for Clean Energy… and a Lot of Dead Bats

July 11, 2016 | Erica Tennenhouse

Mexican free-tailed bats exiting Bracken Bat Cave
Photo credit: USFWS/Ann Froschauer/flickr (CC BY 2.0)

Collisions with wind turbines are killing bats at a staggering rate.

Bats are dying in unprecedented numbers at wind turbines in the U.S., Canada, and Europe. But what motivates bats to embark on dangerous flights through fields of spinning blades time and time again?

Researchers in Germany set out to better understand bat interactions with turbines by fitting 500 bats with miniaturized GPS devices and tracking their movements in and around wind farms.

Writing in the journal Scientific Reports, the researchers observed that in the early days of summer, female bats repeatedly came close to wind turbines. The heights at which they flew — usually between 0 and 140 meters above ground — put them at great risk of collision with turbine blades, which cut through the air at 70 to 130 meters above ground.

Study co-author Christian Voigt proposes an explanation for this risky behavior among females: “In early summer, having just finished raising their pups, the female bats take off looking for new homes and hunting grounds. Conceivably, the bats mistake the wind farm constructions for large dead trees, ideal for serving as bat homes.”

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Male bats, on the other hand, made short trips between their roosts and foraging grounds and tended to fly below the turbine blades.

“These male bats had no reason to venture out,” explains Voigt in the press release. “They had already established their quarters earlier in the year."

Collecting this type of data is important for predicting which bats are vulnerable to collisions with wind turbines. The findings indicate that, at least in midsummer, wind turbines represent a potential threat for colonies of high-flying bat species

The authors suggest that small changes to wind farms could lead to big reductions in bat fatalities. For example, bats only rarely fly at wind speeds above 8 meters per second. Thus, operating the turbines only above that speed would deter bats from approaching wind farms.

Voigt suspects the reason why such operational adjustments are not made more often is that wind farms “already carry the green stamp of renewable energy production. As a consequence, the operators feel that they made a sufficient contribution to environmental protection.”

Nonetheless, Voigt maintains that this clean energy need not be at odds with bat conservation, stating: “Climate protection and the conservation of species are compatible.”

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