Thousands of bats being killed by wind turbines, mistaking them for trees

Andrew Fazekas
ECO 110 wind turbines manufactured by Alstom are seen in the Landes de Couesme wind farm near La Gacilly, western France, April 26, 2014. REUTERS/Stephane Mahe

First it was solar plants incinerating birds, now hapless bats appear to be getting sliced and diced by giant wind turbines. 

According to a study to published in the Proceedings of the National Academy of Sciences this week, air currents around industrial wind turbines may be mimicking those around stands of tall trees where insects tend to congregate. The familiar air currents confuse the poor bats into thinking they may be getting a meal only to draw them in to their deaths.

About 600,000 bats are estimated to have been killed by wind farms in the U.S. in 2012.

For the first time ever, researchers followed the flight movements of bats around the turbines for many months using infra-red imaging video cameras. During periods of low wind, more bats were sighted near turbines than during periods of high wind.

This brewing bat problem appears to be geographically widespread, with documented fatalities around turbines throughout North America, Europe, Africa and Australia.

For some unknown reason, there is also a large variation in the number of deaths from one site to the next.

“Its difficult to generalize given the limited amount of information we currently have on hand, however some areas show consistently high rates of bat fatality, whereas others do not,” said lead author Paul Cryan, a research biologist with the U.S. Geological Survey.

Early evidence is hinting that it may be connected to the height of wind turbines – the taller the the turbine, the more fatalities. Cryan points out that most wind turbines being built today have towers that reach as high as 30- to 40-storey buildings, and this may be crossing the flight paths of bats more often.

Cryan has been trying to figure out what may be the fatal attraction for the bats. He has theorized that the poor creatures may be confusing the turbines with trees – their natural place to socialize, rest during migrations, and most importantly finding insect prey.

And as expected, it appears that tree bat species are particularly at risk. These are species that roost in trees and tend to be the ones that migrate the most. 

According to Cryan and his team, in the United States about 75% of all bat fatalities documented so far involved just 3 species of tree bats: The hoary bats, eastern red bats, and silver-haired bats. There are 45 bat species in the country.  

“This suggests that there is something different about their behaviors that may put them at greater risk,” Cryan said.

Also, most bat deaths around the wind farms occur in the late-summer months through autumn. Again, researchers are not quite sure why this is, but Cryan believes there may be a connection to behavioral changes in tree bats associated with their regular habits.  

Interestingly, similar deaths have been observed recently around solar plants with bats and bird species too. The flying wildlife unknowingly fly through the concentrated beam of sunlight and get fatally scorched.

Cryan and his colleges hope that with this new research, wind energy producers could find better ways of operating turbines during the times of year and weather conditions that might be risky for bats.  

One suggestion is that because gusts of wind may be posing particularly high risks to bats, it might be worth exploring turbines that can function in low-wind conditions when the blades are not turning fast.

Another solution may be to add blinking aviation lights to the turbines, which may prevent bats from mistaking them for trees.

But what is worrisome with these morbid fatalities at wind farms is that bats represent a vital part in keeping natural ecosystems in balance. 

For example, in many regions across the world bats are what keep night-flying insect numbers in check. Insects like beetles and moths can become serious pests for farmers, and these little critters can offer what Cryan calls, “free pest-suppression services.”

“The more than 1,200 species of bats that occur globally provide other important ecosystem services, including pollination and seed dispersal in the subtropics and tropics,” added Cryan. 

“Bats represent a unique lineage of mammalian life that has been flying above our heads and providing us with a source of wonder and mystery for a very, very long time.”

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