News and analysis about energy in California with an eye toward renewables.

Troubling Study Indicates Wind Turbines May Cause Harm To Bat Populations

Bats in a cave in the Tehachapi Mountains | Photo: Random Truth/Flickr/Creative Commons License

A study published in a German scientific journal this summer indicates that wind turbines in one area may pose a serious risk to populations of bats over the better part of a continent. The study, performed by researchers from the Leibniz Institute for Zoo and Wildlife Research (IZW), showed that pipistrelle bats killed at German wind turbines likely originated from countries as distant as Scandinavia, Poland, the Baltic countries, and Russia. An estimated 200,000 bats are killed each year at German wind turbines, raising the possibility that Germany will become a sink for European bat populations -- and raising troubling implications about the effect of wind turbines on California bats.

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The IZW researchers analyzed the fur of killed bats and recorded the ratio of stable hydrogen isotopes in the fur's keratin. Hydrogen has two stable isotopes -- a lighter isotope, H1, with no neutrons, and H2 or deuterium, which has one neutron in its nucleus. The two are chemically identical, but their ratio in the environment varies, with deuterium more common in the north of Europe. As an organism grows, it takes in deuterium in whatever ratio it is available in the environment, providing a geographical marker in the organism's chemical composition. By matching the ratio of deuterium to H1 in fur samples then matching that ratio to a map, the researchers were able to determine where killed bats were raised.

As bats killed at German wind facilities may have come from places 1,000 miles or more away, and as bats have very slow reproduction rates of only 1 or 2 offspring a year, the study suggests that wind turbines in Germany may well be depressing bat populations across the entire northeastern portion of Europe, in an area perhaps a million square miles in extent.

The bats most vulnerable to wind turbine injuries -- which seem to stem mainly from lung trauma from steep gradients in air pressure rather than from collisions -- are migratory species that live in trees. In California, one of the most common tree bats is the hoary bat, which migrates in large groups across a wide swath of North America from Canada to Mexico. Though the hoary bat is unusual among bats in that it can have litters of three or four pups, the German study nonetheless suggests that poorly sited wind turbines in bat migration areas might depress hoary bat populations across the western part of North America.

A 2011 paper by Paul Cryan of the USGS Fort Collins Science Center in Colorado reports that bat deaths have skyrocketed with the advent of wind turbine installations:

Since 2004, unprecedented rates of bat fatalities have been documented at multiple wind energy sites across the United States and Canada, as well as in several European countries. In the United States, bat fatality rates at turbines are variable across sites and regions. Despite standardized and well validated methods for measuring and comparing fatality rates across sites rarely being employed, estimates to date for individual wind energy sites range from just below one bat per installed megawatt per year (bats/MW/yr) to as high as 70 bats/MW/yr. These fatality rates for bats generally exceed the fatality rates of migratory songbirds at wind turbines, and far exceed any documented natural or human-caused sources of mortality in the affected species of bats. Some large wind energy facilities (e.g., 100-300 MW) are estimated to have fatality rates of 10-20 bats/MW/yr, which means that single wind energy facilities are causing the deaths of thousands of bats per year. With approximately 40,000 MW of turbines currently installed in the United States and Canada, and an average published bat fatality rate of 11.6 bats/MW/yr, more than 450,000 bats may already perish at turbines each year in North America. This number might even be an underestimate due to problems with earlier fatality estimation equations and because bat fatality rates appear to be increasing with deployment of larger turbines. [Emphasis added.]

If U.S. wind turbines truly do pose more of a threat to some American bats than the dreaded White Nose Syndrome now devastating eastern Bat populations, then the German study is sobering indeed. It may be that even a few isolated wind installations may harm bat populations across a broad landscape.

As Cryan says, distressingly,

In some parts of the country, bat researchers who only rarely catch hoary bats in the wild can now walk beneath turbines at certain wind energy facilities during autumn and find more dead hoary bats on the ground in a few weeks than they have caught during their entire careers.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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I don't care if there is an iceberg! The lady in state room 2001 is terribly sea sick and we will not disturb her with a violent turn of the Titanic, you fools!

Global warming is extincting, EXTINCTING somewhere between 25 and 250 species, SPECIES, PER DAY, per day, PER DAY, with 30-50% of all SPECIES, not bats, ALL SPECIES at risk of extinction, EXTINCTION, ALL, GONE by 2100.

Don't you have any young people in your lives KCET? What will you tell them of your reporting, today, when they asked where you had your heads burried in 2012? My God.

I thought you Public Broadcasting folks weren't supposed to be beholden to corporate sponsors in the fossil fuel industry. So much for that theory. Or is it the radical, zero proportionality, zero perspective, local, radical 'environmentalists' that are holding your journalistic, not to mention human, integrity hostage?


If this reporting were to be influenced by fossil fuel company sponsorship then our reporting on renewable energy projects would be very different indeed. BO and Shell Oil are quite involved in wind power, Chevron in solar, and fossil-fuel friendly financial and industrial firms such as Bechtel and Goldman Sachs are very much involved in the renewables trade.

Climate change is absolutely an emergency. But loss of biodiversity is, by many scientists accounts, an even larger emergency. We may need to make difficult choices, or -- as seems increasingly likely -- conservation and distributed generation may provide far better, less destructive, more efficient ways of generating that renewable energy, that won't destroy the habitat those species will need if they're to survive. But denying the impacts of whatever we choose to do will help no one.

On a personal level, I've been an environmental journalist since the 1980s and have been working to alert people to the dangers of climate change as an activist since well before that. Whether I thus have my head in the sand as a result of recognizing the existence of more than one huge, intractable problem is open to discussion, I suppose.


The dangers that climate change pose to our wildlands and health should not be swung around like a machete to clear the way for more industrial destruction on our wildlands. Wind companies are just like other industries and profit is their top priority. Making that profit requires the loss of our natural resources.

If we are serious about choosing a more sustainable energy path that cuts our use of fossil fuels while easing the burden on our wildlands, we would be making energy efficiency and distributed generation a higher priority.

I want young people to experience open landscapes, witness wildlife in intact habitat, and see the bats heading out for food at dusk. The easy solution to cutting fossil fuels is to sacrifice more wildlands to the renewable energy industry. The responsible way is to generate clean energy where we live or on lands that are already-disturbed.

I am glad KCET is taking a close look at our energy choices and their impacts.


Wind power is proving to be the right decision for our economy, not only by diversifying our energy supply and stabilizing costs in our energy bills, but also attracting up to $20 billion annually in private investment for our economy.

And to make sure these benefits for outweigh the costs, the wind energy industry has established a long record of proactive, collaborative efforts on wildlife issues and seeking ways to avoid, minimize and mitigate its relatively low environmental impacts.

Since 2003, the wind industry, in partnership with Bat Conservation International, U.S. Fish & Wildlife Service, and Department of Energy, has been a part of the Bats & Wind Energy Cooperative (BWEC), which conducts research to quantify the risks for bats at potential wind energy sites and finding ways to reduce fatalities at operating facilities. However, while higher than anticipated bat mortality occurs at some wind facilities, this is not universally true, and these impacts are far surpassed by the losses associated with White Nose Syndrome, which the wind industry has been an active partner in research designed to understand and combat this devastating disease.

As a clean energy source, wind energy is one of the most compatible with wildlife. Wind energy consumes no water and produces no emissions in the generation of electricity, is the least impactful form of energy production available to our society today. The benefits it provides to both wildlife and humans far outweigh its negligible impacts. No energy source— in fact, no human activity— has zero impact on the environment. Comparatively, the wind industry’s is the lowest, yet, it continually works proactively at minimizing its environmental footprint.

Want to learn more? Visit

John Anderson, American Wind Energy Association