From the field: a potential step closer to reducing the lethal impact of wind energy on bats.


Written by Sara Weaver

Sara Weaver is a doctoral candidate at Texas State University. She is pursuing her PhD with plans of becoming a tenure-track professor at Texas A&M University-San Antonio where she is currently a full-time biology lecturer. She has worked with bats since 2007, although her passion for these magnificent flying mammals began when she visited Congress Avenue Bridge as a child.

Sara and her crew check for bat fatalities at each of the study sites.
Courtesy of Sara Weaver

It may be the holy grail in the effort to reduce lethal impacts of wind energy on bats – a device that can be placed on wind turbines that can safely deter bats, while simultaneously allowing the turbine to operate efficiently.

As part of my dissertation research at Texas State University, and in collaboration with BCI, I recently concluded my field experiment of a newly designed ultrasonic acoustic deterrent (UAD) for reducing bat fatalities at wind turbines. Developed by NRG Systems, the UADs, (as well as field technicians) withstood some of the most rigorous environmental conditions imaginable with temperatures exceeding 100 F throughout most of the study, which took place in south Texas from August 1st through October 31st, 2017.

The idea behind the UADs is to “jam” the bat’s echolocation by creating a disorienting airspace surrounding the wind turbines. Each UAD broadcasts a continuous high frequency sound between 20-50 kHz, which is inaudible to humans but within the range of all bat species occurring in the region.

Newly designed ultrasonic acoustic deterrents (UADs) were tested over the course of three months.
Courtesy of William Ramirez

To test the effectiveness of UADs for reducing bat fatalities, we installed 6 UADs on each of 16 wind turbines at a wind energy facility in Starr County, Texas. Each night during the study, we randomly selected 8 turbines to serve as controls (deterrents off) and 8 turbines as treatments (deterrents on). Thirteen field technicians, unaware of the treatment schedule, conducted daily carcass searches under all 16 turbines. At the end of the study, we compared the difference in fatality between control and treatment conditions.

After a total of 1,388 turbine searches, our results are finally in and we are excited to report that UADs significantly reduced overall bat fatalities by an average of 46%!

For Brazilian free-tailed bats (Tadarida brasiliensis) the results are even better, with an average 51% reduction. 

While our results are promising, this is only a single season study and further testing is necessary to support these initial findings. In addition, we found UADs varied in their effectiveness by species, with no reduction for some, such as the northern yellow bat (Lasiurus intermedius). This indicates there is room for improvement.

The crew withstood rigorous fields conditions with temperatures exceeding 100 F throughout most of the study.
Courtesy of Sarah Perry

Curtailing wind turbines, an alternative impact reduction strategy that alters turbine operations when bats are at risk, also is effective, but results in an unacceptable loss in power production. An added benefit of the UADs is they allow wind turbines to operate normally. With additional studies, we hope to increase effectiveness and demonstrate the potential for UADs to become an industry-wide, commercially available tool for reducing bat fatalities.

This study would not have been possible without Duke Energy Renewables and Vestas Wind Systems, who provided site access and project support. We also wish to thank the funding sources that made this project possible, including Texas Parks and Wildlife Department, Duke Energy, NRG Systems, and Bat Conservation International.