Why wind turbines can mean death for bats

August 25, 2008

Power-generating wind turbines have long been recognized as a potentially life-threatening hazard for birds. But at most wind facilities, bats actually die in much greater numbers. Now, researchers reporting in Current Biology, a Cell Press journal, on August 26th think they know why.

Ninety percent of the bats they examined after death showed signs of internal hemorrhaging consistent with trauma from the sudden drop in air pressure (a condition known as barotrauma) at turbine blades. Only about half of the bats showed any evidence of direct contact with the blades.

"Because bats can detect objects with echolocation, they seldom collide with man-made structures," said Erin Baerwald of the University of Calgary in Canada. "An atmospheric-pressure drop at wind-turbine blades is an undetectable—and potentially unforeseeable—hazard for bats, thus partially explaining the large number of bat fatalities at these specific structures.

"Given that bats are more susceptible to barotrauma than birds, and that bat fatalities at wind turbines far outnumber bird fatalities at most sites, wildlife fatalities at wind turbines are now a bat issue, not a bird issue."

The respiratory systems of bats and birds differ in important ways, in terms of both their structure and their function. Bats' lungs, like those of other mammals, are balloon-like, with two-way airflow ending in thin flexible sacs surrounded by capillaries, the researchers explained. When outside pressure drops, those sacs can over-expand, bursting the capillaries around them. Bird lungs, on the other hand, are more rigid and tube-like, with one-way circular airflow passing over and around capillaries. That rigid system can more easily withstand sudden drops in air pressure.

The majority of bats killed at wind turbines are migratory bats that roost in trees, including hoary bats, eastern red bats, and silver-haired bats. While little is known about their population sizes, the researchers said, those deaths could have far-reaching consequences.

Bats typically live for many years, in some cases reaching ages of 30 or more. Most also have just one or two pups at a time, and not necessarily every year. "Slow reproductive rates can limit a population's ability to recover from crashes and thereby increase the risk of endangerment or extinction," said Robert Barclay, also at the University of Calgary, noting that migrating animals tend to be more vulnerable as it is.

All three species of migratory bats killed by wind turbines fly at night, eating thousands of insects—including many crop pests—per day as they go. Therefore, bat losses in one area could have very real effects on ecosystems miles away, along the bats' migration routes.

Baerwald said there is no obvious way to reduce the pressure drop at wind turbines without severely limiting their use. Because bats are more active when wind speeds are low, one strategy may be to increase the speed at which turbine blades begin to rotate during the bats' fall migration period.

Source: Cell Press

Explore further: US South getting its first big wind farm soon

Related Stories

Bats may be mistaking wind turbines for trees

September 30, 2014

Certain bats may be approaching wind turbines after mistaking them for trees, according to a study to be published in the Proceedings of the National Academy of Sciences.

Bats versus wind turbines

August 19, 2014

Wind turbines are responsible for the death of numerous bats. In a recent study, scientists determined the origin of these animals: they do not only come from local areas but many had been already on a long migratory journey. ...

High bat mortality from wind turbines

November 8, 2013

A new estimate of bat deaths caused by wind turbines concludes that more than 600,000 of the mammals likely died this way in 2012 in the contiguous United States. The estimate, published in an article in BioScience, used ...

Recommended for you

How bees naturally vaccinate their babies

July 31, 2015

When it comes to vaccinating their babies, bees don't have a choice—they naturally immunize their offspring against specific diseases found in their environments. And now for the first time, scientists have discovered how ...

Binary star system precisely timed with pulsar's gamma-rays

July 31, 2015

Pulsars are rapidly rotating compact remnants born in the explosions of massive stars. They can be observed through their lighthouse-like beams of radio waves and gamma-rays. Scientists at the Max Planck Institute for Gravitational ...

Image: Hubble sees a dying star's final moments

July 31, 2015

A dying star's final moments are captured in this image from the NASA/ESA Hubble Space Telescope. The death throes of this star may only last mere moments on a cosmological timescale, but this star's demise is still quite ...

Exoplanets 20/20: Looking back to the future

July 31, 2015

Geoff Marcy remembers the hair standing up on the back of his neck. Paul Butler remembers being dead tired. The two men had just made history: the first confirmation of a planet orbiting another star.

Earth flyby of 'space peanut' captured in new video

July 31, 2015

NASA scientists have used two giant, Earth-based radio telescopes to bounce radar signals off a passing asteroid and produce images of the peanut-shaped body as it approached close to Earth this past weekend.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

barakn
2.8 / 5 (4) Aug 25, 2008
Or produce some sort of annoying ultrasound

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.