Clean Power

Published on February 16th, 2015 | by Joshua S Hill


German Wind Turbines Killing Migratory Bats

February 16th, 2015 by  

A new study has determined that a significant number of bats are being killed by wind turbines in Germany — of which more than two-thirds of bats are in the process of migrating between their summer and winter habitats.


Image Credit: via Flickr, Andy Morffew, CC BY-ND 2.0

A number of studies investigating the effect of wind turbines on birds have found that the actual impact wind turbines have on avians is relatively low. However, according to this new research, published in the European Journal of Wildlife Research, wind turbines’ effects on bats — specifically in Germany — cannot be ignored.

As per the press release provided by Forschungsverbund Berlin e.V., “due to its geographical location in Europe, Germany has consequently a central responsibility for the conservation of migratory bats.”

The Findings

According to the research (as per the press release), each wind turbine causes the death of approximately 10 to 12 bats per year if no mitigation measures are put in place. Naturally, these numbers vary based on geographical location and type, as well as the type of turbine.

However, according to the research, not many of these turbines are believed to have any mitigation measures. This led the researchers to conclude that if all the wind turbines in Germany were put into operation without any mitigation measures, nearly 250,000 bats would die per year. Of these numbers, approximately 70% can be attributed to bats migrating between summer and winter habitat.

“We assume that only a fractional part of all 24,000 wind turbines constructed until 2014 meet the necessary standards for the conservation of protected species,” said one of the report’s authors, Christian Voigt, biologist and bat researcher at the German Leibniz Institute for Zoo and Wildlife Research (IZW). “Many, especially old, turbines run without any or only insufficiently implemented mitigation measures.”

The Bias

In reading the press release, however, one cannot help but notice a significant bias towards bats and against wind turbines.

“Not all things that are called “green” serve the purpose of nature conservation,” write the authors of the Forschungsverbund Berlin e.V. press release. They add that “many wind turbines are erected in Germany in order to increase the production of renewable energy by 30% until 2020. These turbines kill bats and are in conflict with national and international nature conservation legislation and international treaties such as the UN Convention on the Conservation of Migratory Species of Wild Animals”.

All of these things may be true, but as was the case for migratory birds and bird deaths at the hands of wind turbines, the whole story was often ignored in favor of sensationalizing out-of-context numbers.

Example, Birds

Not only did many birds not suffer at the blades of wind turbines, but in many cases it was the construction of the wind turbines that proved to be the most troubling factor.

Furthermore, further research found that wind turbines played a comparatively minor role in the death of birds when compared to other energy generation sources — for example, coal.

bird deaths

As can be seen in the above graph, courtesy of the U.S. News and World Report which took it upon itself to look at the numbers of birds killed each year by electricity sources in the US, the number of birds that meet their maker at the hands of wind turbines is comparatively small when compared to coal.

And of course, nothing comes anywhere close to causing bird deaths more than the cat, which on the whole manages to kill anywhere between 1.4 and 3.7 billion per year!

Finally, a study published at the end of 2014 showed that, in many cases, seabirds avoid collision with wind farms.



The above figure, courtesy of Desholm & Kahlert (2005), on Avian collision risk at an offshore wind farm. Biology Letters 1: 296-298, represents flight trajectories of migrating waterbirds within and outside an offshore wind farm.


Back to Bats

Finding similar research for bats is very difficult. News out of the Leibniz Institute for Zoo and Wildlife Research in August of 2014 showed that the migration of bats is thoroughly under-researched right now.

“Owing to decades of bird banding, ornithologists already know much about the migration of birds,” said Gunārs Pētersons, associate professor at the Latvian University for Agriculture. “However, the study of bat migration is still in its infancy. This is due to the fact that there are very few places worldwide where it is possible to observe and catch migrating bats in sufficient numbers.”

The only bat migration number I could find was out of Zambia, by way of travel website My Destination, which stated that visitors to the Kasanka National Park might have the chance to witness the “largest mammal migration in the world” — ie, the migration of 10 million fruit bats.

Using this as an outlier for bat migration numbers — a figure that I found virtually impossible to find for Europe, or Germany specifically — we can halve that and suggest that Europe might see a species of bat migration in the range of 3 to 5 million, which would put bat deaths at between 5 and 8.3% of the total number of bats migrating over Germany.

These numbers are highly speculative, but hopefully raises the fact that further questions need to be asked about this research: what percentage of bats migrating over Germany are actually dying as a result of wind turbines. Is it an excessive number? What legitimate mitigation can be implemented to bring these numbers down, regardless of percentages?

Wind turbines should not take precedence over wildlife conservation, but nor should wildlife conservation override any and all renewable energy development. Without a doubt, further research is necessary, and European wind development will need to begin integrating bat migration into their ecological assessment.

Complete our 2017 CleanTechnica Reader Survey — have your opinions, preferences, and deepest wishes heard.

Check out our 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

Tags: , , , , , , , , , , ,

About the Author

I'm a Christian, a nerd, a geek, and I believe that we're pretty quickly directing planet-Earth into hell in a handbasket! I also write for Fantasy Book Review (, and can be found writing articles for a variety of other sites. Check me out at for more.

  • Larry

    Maybe some mad scientist can genetically modify the bats so they avoid wind turbines

  • shecky vegas

    Here’s another thing – wind turbines create sonic vibrations which cause the udders of nearby cows to undulate excessively insothat when the teats are squeezed, you don’t get milk. You get cottage cheese. It’s true, I swear, it’s true.

    • Bob_Wallace

      Canadian cows, don’t they give soft serve ice cream when close to turbines?

      • Larry

        Black cows give chocolate soft werve

  • Pete Austin

    Bullshit. The high numbers of bird deaths due to coal are almost entirely due to the assumed effect of future climate change calculated from climate models..

    It’s likely that a slightly warmer world with more CO2 would have more vegetation (because CO2 is basically plant food), meaning more food for more birds, and that these extra birds would eventually grow old and die, but this is a good thing – whereas windmills killing birds and reducing the bird population is entirely bad.

  • Bob_Wallace

    Two ways to reduce bat kills have been found and implemented. First, there is some bat migration and during the couple of weeks that this is occurring turbines are turned off at night where migration is underway.

    Second, bats fly looking for insects. Insects can only fly around when wind speeds are lower. In areas where bat kills have been happening turbines use a higher start speed at night, they don’t start rotating until winds are high enough to ground insects.

    • Sir Alfred

      CORRECT, you don`t see insects in windy conditions.not even flies.

    • Adam_Antatheist

      Bat lovers should be thankful that the average capacity factor for all of 2014 was just 15.85%, instead of what we’re lead to believe, which is nearly double that figure.

      It must mean that on average the blade speed is only half of what most people think it should be – doesn’t it?

      • Bob_Wallace

        Germany is repowering its onshore wind.

        Those low numbers will become part of history.

        • Bob_Wallace

          People talk about US wind capacity in the 30% range. It’s moving up as technology improves. Here’s a partial from an email from GE –

          “While we cannot share specific numbers from our customers’ sites unless they release it already or it’s public information, but we’re definitely seeing some above 50 percent capacity factors at many farms.

          Capacity factors obviously vary across wind farms due to a wide range of site locations and other factors. GE wind turbines in farms across the United States—in states such as Montana, California, Nebraska, Oklahoma, and Kansas—have reached capacity factors of over fifty percent over the last two years (2013-14).

          These sites include a variety of GE wind turbine models and installation dates, and each site has registered capacity factors ranging from 50.4 to 52.4 percent, including availability at around 98 percent.”

          And I’ll tack on a graph of Danish offshore wind which will let you see how CF has increased over time.

          Just a bit more to puncture your anti-renewable bubble –
          early commercial solar panels were wimps compared to today’s. Technology on the march.

          • Bob, wondering if the IESO (Ontario) would be able to provide the capacity factor for the greatly expanding wind energy centers here in Ontario.

            They publish the “Hourly Wind Generator Output, 2006-present” as an XLS here:

            Problem is, the output keeps growing as new wind farms come online. And some legacy farms have had expansion/contraction in #’s of turbines. Without the total maximum capacity available as an item on the sheet, there is no way to accurately calculate the CF.

          • Bob_Wallace

            Contact them and see if they will help you out.

          • So I took the spreadsheet, subset to the wind farms producing since Jan 2013 and found ~ 28% capacity factor (CF). I then subset the largest wind farms built in On/Before Jan 2014 and found ~30% CF. Pretty consistent in the data. Onshore wind in Ontario is nowhere near as brisk as the great plains states in the US. Unfortunately due to NIMBY, no offshore farms yet exist in the great lakes. However, many of the newer onshore farms are adjacent to the lakes and high enough to be above the tree line.

          • Bob_Wallace

            If those are accurate numbers then they are low based on what is being reported in the US. The AWEA has said that new US wind farms are returning CFs above 40% and, as seen, GE is reporting some over 50%.

            Modern wind turbines are mounted 80 meters or more above ground.

            Capacity increases are very recent. The real tell might be a farm built in 2014. Look at its CF in 2016 after it has had a little time to work out any bugs that might be present.


            From the latest IESO forcast document, here are the actual numbers (monthly):

            Month WCC (% of Installed Capacity)
            Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
            33.1% 33.1% 26.2% 22.4% 23.4% 13.6% 13.6% 13.6% 16.7% 21.6% 28.6% 33.1%

            Remember, the vast majority of the wind power in Ontario has been stood up within the past 3 years, and growing at >1GW/year.

      • Hans

        Please provide link to source. Don’t confuse capacity factor with operating time.

  • Doug Cutler

    Last year 100,000 Australian bats fell from the sky in an extreme heat, so . . .

  • Steven F

    I think thisis the study the article is based on.


    In this study they found 136 dead bats at 45 sites over a period of 10 years. No mention was made of how may turbines were involved. Thats 13.6 bats a year. I think there sample size is too low to accurately calculate the bat fatalities and might be substantually overestimating the number of deaths.

    • Hans

      I don”t have access to your C-drive 😉

    • Philip W

      Haha great, it’s been a few years since I last saw somebody make that mistake 😀
      You pasted a local link from your computer, we can do absolutely nothing with that. 😉

  • Sir Alfred

    With a small amount of inventiveness, guards can be constructed to prevent birds and bats from being stupid enough to fly into these ugly fans, but then really does anyone care about bats, they are disease carrying animals that are far from pets.
    these very ugly fans have to be 99% better than burning coal and diesel oil.

    • Dan Hue

      First, wind turbines are not ugly. They are majestic. Second, yes, we care about bats too. They are hugely helpful in controlling insects, and are really cute too. Incidentally, I don’t think they are killed by flying through the blades, but rather by the low pressure behind them, which bursts their lungs.

      • Sir Alfred

        Who in hell gave you that information ? if the blade were rotating that fast to create that amount of pressure drop the blade would fly off ,they are not jet engines, As for lovely little animals ask the poor people they live in their locality`s what they think, and the children that have to beware of them coming and going from some schools.
        As for the amount killed again look at the numbers, not even worth mentioning.

        • Bob_Wallace

          I’m pretty sure there’s some truth behind the pressure differential bat kills. I don’t have the energy to dig out the studies at the moment, but you might wish to do so before dismissing out of hand.

          • Bob_Wallace

            And then I find this and start retracting…

            “For years scientists have speculated that the unexpected number of bat fatalities around wind farms is the result of barotrauma-related injuries. The barotrauma hypothesis suggests that a significant number of bat fatalities are due to internal bleeding caused by rapid changes in atmospheric pressure around operating wind turbine blades. But according to a recent National Renewable Energy Laboratory (NREL) study that was presented at the ninth biennial Wind Wildlife Research Meeting in Denver, Colorado, November 27-30, 2012, it appears unlikely that the pressure changes around operating wind turbine blades are large enough to cause fatal barotrauma.”


            Anyone know of a recent summary paper from a reliable source? Bat stuff needs to be pulled together.

        • JamesWimberley

          What threat do bats create for children? Vampire bats only exist in Central and South America; there is a tiny risk of transmission of rabies, which should be taken seriously there, but it’s nonexistent in Europe and the USA. I suggest your distaste for bats is merely prejudice.

          • nakedChimp

            James, In my neck of the woods they have bat/flying-fox colonies in the city in trees.. they cause dirt and damage the trees (after humans destroyed habitats and the animals like it in the city too).
            Anyhow.. there is some virus thing that goes from bats to horses and can possibly go onto humans as well, so people call for culling/relocating (latter doesn’t always work and/or is costly).

  • Larmion

    That wind turbines kill significant numbers of bats, unlike birds, is hardly news. Bats generally have poorer collision detection and avoidance strategies than migratory birds and fly at different altitudes and speeds.

    Fortunately, there are already devices being tested to repel bats from turbines. Their exquisite sensitivity to high frequency sounds offers one approach: place low cost high frequency generators on nacelles and voila. Curtailing turbines sited in migration routes at the right times can also help greatly: most migration activity seems concentrated during a few short months a year and mainly at dusk or dawn (depending on bat species).

    Bats have been given too little attention. Environmental impact reports for wind farms bulge with long studies into potential effect on birds, but often mention bats only in passing. Too often, it’s assumed that what works for a bird will work for a bat, which is absurd.

    • Steven F

      “That wind turbines kill significant numbers of bats, unlike birds, is hardly news. Bats generally have poorer collision detection and avoidance strategies than migratory birds and fly at different altitudes and speeds.”

      when I was young visiting our uncle in North Dakota there were a lot of bats out. We tried hitting them with brooms. No mater how hard we tried we always missed From my experience they have excellent collision detection and avoidance capabilities. Since they often roust in caves with narrow openings, tight turns, and obstacle, I would expect most species to have similar capabilities as the ones I saw.

      • Pete Austin

        The tips of turbine blades move much faster than your broom, and they are 1000x bigger, which makes them almost impossible for bats to avoid.

    • JamesWimberley

      Thanks. The report says nothing about the “mitigation measures” being discussed. Is any work being done on the sound reflectance of blade coatings, since bats navigate by sonar?
      Another factor could be height. European bats are insect-eaters, so presumably don’t fly high normally. You would also expect the shift to bigger turbines to reduce the risk of collision per kwh on general statistical grounds.

  • RobMF

    The mortality rate is very low as a percentage of the total population. Many more times these numbers are likely killed by predators or by coal, which wind directly replaces. In any case, my experience is that most of these studies are funded by fossil fuel companies and are, notably, slanted and exaggerated to the point of acting as propaganda pieces against the broadly helpful wind farms.

    It’s also worth doing a study on the population impact of climate change on bats. Most studies I’ve seen show that climate change drives numerous bat species into extinction. So, in removing fossil fuel use, wind turbines are actually saving bats as a whole, despite relatively minor instances of individual death.

    • Larmion

      Wind is likely much better than coal on the bat front, that’s true (although I haven’t seen any figures about bat deaths due to coal and it’s dangerous to extrapolate bird figures).

      However, that’s missing the point. Few authors say ‘let’s ban wind farms because they might kill some animals’. What they say instead is ‘covering a tiny percentage of the world’s surface with wind farms is enough to supply all the energy we could ever need. So let’s make sure that we choose that tiny percentage with the greatest care possible to avoid bird and bat deaths’.

      And that’s sensible. If you look at mortality rates for wind farms, you’ll find a very low average value but with quite a large variance. In other words: a small number of poorly sited wind farms accounts for a large share of all fatalities.

      Another point you’re missing is that 10 death birds aren’t always better than 1000. Why? Because not all birds are equally threatened. Killing 1000 rock pigeons isn’t generally going to fundamentally alter an ecosystem or threaten a species with extinction. Killing 10 rare birds might. That’s why many European wind projects have been moved or scaled down slightly despite models predicting a small absolute number of deaths.

      Before I’m beginning to sound like an anti-wind campaigner, I must point out that I’m not. I’ve invested quite a bit of money in local wind farms and love wind power greatly – what’s not to love about a power source that wins both on cost and on environmental impact?

      But wind turbines have to be sited properly. We are now properly taking effects on birds into account, at least in developed countries. But effects on bats continue to be poorly understood and must be investigated in depth. Might that mean a handful of promising wind turbine sites will be rejected? Probably. But will it slow down wind development in a meaningful way? Not at all.

Back to Top ↑