Media & Education
BATS Magazine

Volume 27, Issue 3, Fall 2009

Softening the Blow

New wind-energy research could help reduce bat kills

By Rebecca Patterson

The morning sun is barely rising over the forested Pennsylvania ridge top when three giant blades twist slowly to catch the wind and begin rotating on their 263-foot (80-meter) tower. Electricity starts flowing from the wind turbine almost immediately.

And soon after, a team of BCI field biologists in bright-orange vests and hard hats begin scouring the fields surrounding this and other turbines at the Casselman Wind Power Project. On this balmy July day, the biologists are collecting data and searching for bat carcasses, just as they did during the freezing rains of early spring. The turbines and the biologists are both part of an experiment designed to reduce the number of bats that are being killed at wind-energy facilities around the United States and elsewhere.

Ed Arnett, BCI's Co-director of Programs, arrives at the Iberdrola Renewables wind farm with two assistants, a pair of chocolate Labrador retrievers – experienced hunting dogs trained to search for bat carcasses under turbine blades. The dogs are skilled at spotting dead bats in waist-high grass and other daunting terrains. This experiment could prove extremely important, and it was a long time in the making. Arnett is here to help ensure the project's success.

The idea for this study was first proposed at the initial meeting of the Bats and Wind Energy Cooperative (BWEC) in 2004. The BCI-led program was formed in response to an alarming number of bat fatalities discovered at a wind-energy facility at Mountaineer, West Virginia. This unusual collaboration of conservationists, industry and government was charged with prioritizing and conducting research designed to reduce bat kills at wind turbines. BWEC was founded by BCI, the American Wind Energy Association, the National Renewable Energy Lab and the U.S. Fish and Wildlife Service. Arnett is the BWEC Coordinator.

Tens of thousands of bats are being killed at wind farms in the eastern United States each year in collisions with the spinning turbine blades and from related causes. Nationwide, confirmed bat kills include 12 of the United States' 46 bat species. Little brown myotis (Myotis lucifugus) are common wind-power victims, almost 25 percent of bat kills at some sites – and also the hardest hit by White-nose Syndrome. Reducing wind-power mortality becomes especially urgent among bat populations that are being simultaneously devastated by WNS.

Studies at Mountaineer and at Pennsylvania sites showed that bats were most often killed during migratory periods and on nights when wind speeds were low. (Subsequent research finds that roughly 85 percent of bat deaths occur during the fall migration from late July through mid-October.) This led BWEC scientists five years ago to propose a test of the hypothesis that curtailment – shutting down wind turbines during low-wind periods at night – could reduce the number of bat fatalities. During such periods, relatively little electricity was being produced, which minimizes the costs of curtailment.

But persuading the wind industry to temporarily shut down perfectly serviceable turbines in hopes of saving bats proved to be a tough sell. After being rebuffed by several wind-energy companies, BWEC scientists were finally able to test the curtailment hypothesis last year.

The world's leading provider of wind power, Iberdrola Renewables (formerly PPM Energy) allowed BWEC scientists to use the Casselman Wind Power Project for the study. The first U.S.-based curtailment experiment was conducted from July through October 2008, and researchers were back beneath the turbines again this year.

"We are proud to offer our Casselman site for this important experiment and fully support efforts of the BWEC," Andrew Linehan, Iberdrola Renewables director of permitting, said. "We ... recognize there is an impact on bats that requires scientific study."

The BWEC team monitored fresh bat kills daily at 12 of Casselman's 23 turbines from July 26 through October 10. Each night, four randomly selected turbines were left to operate normally, kicking into action when wind speed reached 7.8 miles per hour (3.5 meters/second). The other eight were set to remain idle until winds reach 11.2 to 14.5 mph (5 to 6.5 m/s). Researchers found no significant fatality differences between the two experimental wind-speed thresholds. Ten other non-curtailed turbines, monitored for a separate study, were used for comparison as a second control group.

Our initial results are certainly promising. At Casselman, nightly bat fatalities were 53 to 87 percent lower at curtailed turbines than at fully operational units. The average drop in bat kills was 73 percent per night. These figures are consistent with the 50 to 60 percent reductions reported from two similar curtailment studies, one each in Germany and Canada. BCI scholarships and other grants helped support research led by the University of Calgary in Alberta, Canada ("Prairie Winds," BATS Fall 2007).

The study also found that temporarily stopping turbines on low-wind nights results in minimal power losses annually. If the temporary curtailment procedures were applied to all 23 Casselman turbines during the migration period of approximately 21?2 months, total electricity output for the year would be reduced by less than one percent.

With the number of wind-energy projects growing rapidly around the country, it is vital that scientists demonstrate feasible methods for sharply reducing the number of bat fatalities and that wind-power operators adopt them.

While continuing their curtailment studies, BWEC scientists also are conducting the first tests of a prototype acoustic deterrent at operating wind turbines. The device is designed to broadcast ultrasonic noise that should interfere with the bats' own echolocation-based navigation system to such an extent that the animals steer clear of the turbines. BWEC is deploying the devices on operational turbines to determine their impact on bat fatalities. Once again, Iberdrola Renewables stepped forward to support critical BWEC research and is hosting the deterrent study at a different Pennsylvania facility.

We are making progress toward the day when bats and wind turbines can share the landscape without littering the ground with carcasses. But the expanding wind industry will not wait for the results of conservation science. BCI researchers face a tight deadline as more bats are dying every day. But with the continued support of BCI members, government and industry, we will reach this goal.

Rebecca Patterson is the Programs Assistant at Bat Conservation International.

Rebecca Patterson is the Programs Assistant at Bat Conservation International.

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