(Photo by e_monk via Creative Commons)

Bats & blades: More research needed on bat, wind farm fatalities

Altamont Pass in California is one of the world’s largest wind farms — and most notorious among bird lovers. Much of the anxiety around wind turbines and raptor collisions comes from the large number of eagle fatalities reported from this single cluster of wind farms east of the Bay Area.

In 2005, the wind farms’ operator sought to reduce bird deaths by replacing 126 turbines with 26 larger ones that rotated more slowly and that were spaced farther apart. Over the next few years, bird collisions with the newer turbines were 66 percent lower compared to the older turbines.

But there was an unexpected side effect: bat fatalities were 800 percent higher on the newer, larger turbines.

When it comes to preventing wildlife fatalities at wind farms, scientists are learning that bats are indeed a whole different animal than large birds.

Strategies that have worked for minimizing bird collisions have been ineffective, or in some cases counterproductive, for bats, which play a critical role in plants pollination and provide billions of dollars worth of free pest control to the nation’s agricultural industry.

A fatal attraction?

Laura Ellison is an ecologist with the U.S. Geological Survey in Fort Collins, Colorado, who has spent the last 20 years studying bats and other small mammals. Earlier this month she presented on the bat and wind farm issue at the North America Congress for Conservation Biology.

“The newer, larger turbines seem to be worse for bats,” Ellison said in an interview last week. Researchers are just scratching the surface in understanding why that is.

A few theories exist for why bats and blade collisions occur. One is that bats just happen to be in the wrong place at the wrong time, but there’s also evidence that bats, particularly tree bats, are actually attracted to wind turbines.

“Video recordings are showing that bats are just going towards these turbines. They see this tall structure on the landscape, and they’re very curious,” Ellison said.

They might be scoping turbines out as potential roosting sites, or maybe as places to meet a mate. Another hypothesis speculates that insects gather more densely around turbines.

The attraction theories might explain why siting decisions haven’t seemed to have worked in preventing bat collisions. With birds, building farms away from prime habitat or migration flyways is promoted as the best way to prevent collisions, but that hasn’t worked for bats.

“There doesn’t really seem to be a pattern,” Ellison said. Wind farms have been built in areas with little bat activity, but after construction they experience scores of bat deaths.

More research needs to be done on siting issues, she said.

Bat behavior a mystery

It doesn’t help that we know relatively little about bat migration patterns. The small, nocturnal creatures are much tougher to study than birds. They roost in hard-to-find spaces and are active at night when they’re hard to see.

How many bats are killed annually by wind turbines? No one has a precise number, but the magnitude is undoubtedly in the thousands per year, Ellison said. “Most bat biologists don’t think that this is sustainable in the long run, with those type of numbers that are being killed,” she said.

Studies of individual wind farms have found mortality rates ranging from one bat per megawatt per year to 70 bats per megawatt per year. The variation makes it hard to extrapolate a reliable national estimate.

There aren’t any consistent mandates or methods for counting bat fatalities, and many factors that can skew the results. Carcasses can be hard to spot in certain habitats, and they’re easy snacks for scavengers. Different companies use different methods for accounting for these factors.

Another variable is “searcher efficiency” — some people are better at spotting dead bats than others. Researchers are experimenting with using scent dogs to find bat carcasses. They seem to perform better than people, but even canine noses have variation in their performance.

More research needed

Ellison said she’s not in a position to tell wind farms what do to, but she stressed the need for more research. That can be aided if wind farm developers help collect data about bats, in both pre-construction studies and regular surveys after that.

A lot of research is being done on potential bat deterrents, from acoustic frequencies to laser lights, that might be used to keep the animals from flying near blades.

Acoustic sensors are being placed at wind farms to study bat activity around them. Researchers are also using radar to try to better understand bat movements on a larger scale around the Great Lakes region, Ellison said.

Bat fatalities are most common in the fall, when tree bats are migrating, and they appear to be particularly active on nights with low wind speeds. One strategy that seems to work best for reducing collisions is to turn off turbines on fall nights when wind speeds fall below a certain threshold.

You can read Ellison’s report, Bats and Wind Energy—A Literature Synthesis and Annotated Bibliography, here.

4 thoughts on “Bats & blades: More research needed on bat, wind farm fatalities

  1. ““There doesn’t really seem to be a pattern,” Ellison said. Wind farms have been built in areas with little bat activity, but after construction they experience scores of bat deaths.” Perhaps Ms. Ellison should head out to see if the information in survey’s is verifiable. The AWA Goodhue project in Minnesota is instructive. You find that there is a disconnect between reality, and the perception wind energy developers want to create. The bats were there before the turbines went in…..the developers just didn’t record their presence.

  2. Regarding search efficiency; I have noted that wind developers and their biologists have an extremely difficult time spotting dead bats. They have a hard time finding live bats and birds as well. It’s amazing what you can’t find when you’re trying not to. Speaking of inefficiency, since the only thing turbines actually do is transfer wealth, primarily to Wall Street and European wind companies (with a little trickle to rural landowners) it would be more efficient to simply transfer the wealth without installing turbines. There would be fewer negative side effects too. T. Boone Pickens is open to having some of that wealth as long as he does not have to host turbines on his property.

  3. I looked over the studies than claim that the new turbines at Altamnont are safer. They are not in any way safer and the studies belong in the trash. This is because of clear wind industry bias and bogus methodology. These so called “safer” turbines also killed more eagles. The bat fatalities at Altamont have always been grossly (at least 100 times) under reported because the idiotic body searches always on 30-90 day cycles. The searches that found more bats were conducted on 14 -15 day cycles so they found more bats before the scavengers ate them. Well DUH!!!!!!!!!!! For decades wind industry mortality studies have been deliberately designed with flawed methodology. Examples of this flawed methodology include searching turbines that are not operating, by looking in a small search areas around the turbines, by looking bodies every 15 or 30 days instead of looking every day, by not using trained dogs which could quickly find every fallen bird or bat, by not counting the permanently disabled or mortally wounded, and by allowing employees/lease holders to pick up bodies.

    At this point studying the impacts of wind turbines on bats and birds is a waste of time. Every study conducted by the industry over the last several decades has been conducted to hide the death toll as much as possible and make it look like they are doing something about this terrible impact. But these monstrosities are mass killers of anything that flies and there is no way to make them safe. So all this is about as meaningful as studying the effects of center-fire bullets hitting your skull to see if you can make them safer.

    Over the last 6 years several hundred Whooping Cranes have gone missing and their critically endangered population is rapidly declining. This year over 100 whooping cranes went missing and most of the lost members probably fell victim to the wind projects in the central flyway. Can’t wait for the bogus study on this to come out.

  4. studies have found that bats don’t actually get hit by blades. they are world class acrobats. you can string fishing line wall-to-wall in a dense web in a pitch black room, and bats will dart through the obstacles like they aren’t even there. the problem appears to be that bats can’t see the invisible low pressure zones that trail the blades. they try to fly through the swept area, and their blood vessels pop.