Coexisting With Bats

This year wind energy companies are increasing their support for critical wildlife research at a crucial point in the continued development and maturation of the wind energy industry. The Bats & Wind Energy Cooperative (BWEC), a collaborative research effort, is now entering its second phase, and some of the biggest industry players are stepping forward to support it.

The issue of bats and wind turbines is one that cropped up relatively recently. During the industry’s first two decades, studies conducted at wind projects around the country designed to monitor possible bird fatalities ended up finding that some bats were being killed; however, the low numbers never raised any significant alarms.

It was not until an avian study in 2003 at a project in West Virginia discovered relatively high numbers of bat fatalities that the issue became the most significant wildlife concern for the wind energy industry.

When bat fatalities were discovered in the East, the industry recognized that moving quickly to understand the issue and resolve it was key. The American Wind Energy Association (AWEA) joined with Bat Conservation International, the Department of Energy’s National Renewable Energy Laboratory (NREL), and the U.S. Fish & Wildlife Service to form BWEC. BWEC is designed to recommend, fund, and review scientific research aimed at understanding how bats and wind turbines interact and how to minimize impacts to bats at wind energy projects.

The collaborative nature of BWEC has not always been easy to navigate, but the hard work has already paid off, for the result has been credible science produced efficiently and effectively, with all parties’ funds well-leveraged.

A Nascent Science
BWEC came into being in response to a situation made more complex by the unique attributes of bats. As the wind industry became involved with the research, industry participants were somewhat surprised to learn how little is known about bats. The bats killed at wind projects are, for the most part, solitary tree-roosting species. Since these kinds of bats are active at night and are not found together in caves, it is difficult to know much about their population sizes or their activities in particular conditions.

Moreover, bats are different from birds in some important respects: they are mammals, they tend to live longer than most birds, and they have relatively few offspring (and, consequently, are probably less able as species to replace individuals that die in collisions).

The combination of what little is known about bat population sizes, and the potentially significant impact collisions with wind turbines might have, called out for an immediate response. Thus, the Bats & Wind Energy Cooperative was formed.

As BWEC launched in early 2004, the research program came together quickly. The first priority was to understand how bats were being killed by the turbines. Were they running into the stationary towers or the spinning blades? Under what conditions? Were the bats attracted to the turbines in some way? Not all of the answers became clear in the first year of research, but a picture began to form.

In 2004, BWEC began an intensive fatality monitoring program at the Mountaineer project in West Virginia and a second wind project about 60 miles away over the Pennsylvania border. Thermal imaging cameras recorded bats near turbine blades, and even a couple of strikes. It is thought that about 2,000 bats were killed during the six-week research period. The information collected provided a path forward for research aimed directly at reducing fatalities at wind energy projects.

The next phase of research in 2005 and 2006 took a number of directions. The questions became:

• Do turbines produce ultrasonic sounds that attract bats?
• Is there data that can be collected before a project is constructed that shows whether a site is risky for bats?
• Can an ultrasonic acoustic device be developed to deter bats away from turbines?

The first question was relatively simple to research and involved measuring the ultrasound emissions at wind turbines. Studies revealed that, in fact, ultrasound levels recorded at the base of the turbine were quite low and therefore were not a likely attractant to bats. Some further investigation may be needed to measure ultrasound emissions at the top of the turbine tower.

The next two questions require a much more detailed, multi-year investigation at multiple sites, and that work has already begun. Pre/post-construction data collection and analysis began at one site in Pennsylvania and has since been expanded to other sites now under development. Such work is crucial because, again, bat research sometimes poses unique challenges that are not even present with respect to avoiding problems with bird fatalities.

Before building a wind project, developers are usually required to study bird species in the area to determine whether the site will pose a threat to resident or migrant birds there. The kind of information that needs to be collected is relatively consistent across sites, depending on the avian species. Bats, however, are different, and specialized equipment is required to monitor their activity at proposed facilities.

Few pre-construction bat studies have been performed, and none have been linked with post construction fatalities to determine if in fact risk can be predicted. Thanks to stakeholders’ efforts, progress continues to be made on that front. Acoustic monitors have been placed throughout potential sites in different habitats and at varying heights to record bat calls over many months.

This data will determine how much activity among different species of bats occurs at the site. That information can be correlated to weather data and then compared to post-construction fatality monitoring. Results should help researchers determine what kind of information can be used to predict bat mortality at a site so that the riskiest sites can be avoided or more robust mitigation measures can be taken.

“It is critical for everyone involved to make sure that the pre-construction data being collected actually answer the questions being asked,” said Ed Arnett, project coordinator for the Bats & Wind Energy Cooperative. “The industry and permitting agencies need to know how to determine risky sites for bats.”

BWEC is also involved in developing a possible acoustic deterrent that could perhaps warn bats away from wind turbines.

A prototype mechanism was created and tested in the laboratory and the field in 2006. The device is designed to emit ultrasonic acoustic stimuli at a level that would not attract bats but rather flood them with noise and jam their ability to hear anything but the device, similar to the situation in which a person who is near a jet engine can only hear the engine.

In this situation, it is expected that a bat would avoid the area around such a device. Early results showed some promise, so the decision was made to scale up this area of inquiry and test some different prototypes on wind turbines.

That work began at a project in New York this fall, during the bat migration season, when most of the bats killed by wind turbines have historically been found.

“It is far too early to claim that this acoustic deterrent is a solution,” said Arnett. “But it does warrant more investigation, and so that is why we are pursuing it further.”

Next Steps
Great work is being done by BWEC, but much more is needed. As the cooperative enters into the next three-year phase, research efforts will continue and expand. The pre/post-construction research projects will continue and should start producing some informative results now that the wind energy projects are under construction. Work on the acoustic deterrent, meanwhile, is progressing, and extensive testing will be needed to determine its effectiveness.

One preventive practice researchers wanted to pursue earlier, a technique known as “feathering” turbine blades in lower wind speeds, is expected to commence at a project as early as 2008. Feathering a turbine means turning it out of the wind, which greatly slows or even stops the blades from turning. Monitoring in 2004 found that bats were more likely to collide with turbine blades during low wind conditions, and no bat fatalities were found at one turbine that was not operating.

So, the thinking goes that turbines could be curtailed during some lower wind times in order to reduce the number of bat fatalities. The economic impact of turbine curtailment to wind facilities, even under limited conditions, is unclear at this point; therefore, this research is still to come. Such are not yet available.

The Importance of Collaboration
Wind energy companies are stepping up to support the critical research concerning bats and wind power. AWEA raises money from member companies to fund BWEC’s research, and the response this year has been encouraging. Industry funds are pooled with money from contributors to Bat Conservation International (BCI), an annual grant from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), and money from state energy funds.

“I think the lesson we have all learned from BWEC is the importance of collaboration,” said AWEA’s Communications Director and BWEC Oversight Committee member Tom Gray. “By working with BCI, the U.S. Fish & Wildlife Service, and NREL, we are seeing high-quality research that everyone agrees is necessary to allow wind turbines and bats to coexist. We know it can be done, but not without the cooperation of these parties and the support of the industry. I might add that BCI has been a very effective partner, contributing a significant portion of the research funding.”

Laurie Jodziewicz is a communications & policy specialist with the American Wind Energy Association. Any companies interested in supporting this important research effort are encouraged to email her at

This article was republished with permission from the American Wind Energy Association.

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