Causing an animal to become uncomfortable, disoriented, and unable to find food is typically viewed as cruel behavior. But when it comes to bats, researchers are doing just that—and it may save their lives.
Scientists are testing a new device that may decrease insect-eating bats’ attractions to wind turbines. The instrument emits ultrasound, or sound with a frequency greater than humans can hear, but is audible to certain animals like dogs and bats. Over the next several weeks, scientists will see if ultrasound deters the flying mammals from going near turbines on wind farms in Oregon and New York. If the tests are successful, the speaker-sized devices could be attached to wind turbines to repel bats, which are frequently killed at night by the swiftly rotating blades.
“Such a deterrent would be a wonderful thing,” says John Hayes, a wildlife ecologist at the University of Florida who is not involved in the study.
The project is spearheaded by the Bats and Wind Energy Cooperative (BWEC), an alliance of government agencies, academics, and wind industry representatives that aims to reduce the threat of wind turbines to bat populations.
The drive to save bats stems from their important ecological role: The winged creatures make up about a quarter of the world’s mammals, keep insect populations in check, pollinate plants such as agave and bananas, and disperse seeds.
But as more and more wind farms pop up across the country, some bat populations have taken a hit. Fatalities have been reported at most wind energy facilities in the US, and one turbine can kill as many as 50 bats per year. And the wind industry continues to expand: It grew 27 percent in 2006 and is expected to grow an additional 26 percent in 2007, according to the American Wind Energy Association (AWEA). If the trend continues, researchers estimate that there will be more than 30,000 turbine-related bat fatalities in 2020.
The BWEC is racing to determine why the nocturnal flyers are attracted to turbines, and to figure out ways prevent the deaths. Few studies have been done to answer these questions because the danger wind turbines pose to bats has only been recognized in the last several years. And because it’s difficult to accurately survey migratory bat populations in the first place, coming up with a successful solution is a complex process.
“We know so little about bats and their populations, it’s truly a challenge to understand the significance of these mortalities.” says Ed Arnett, project coordinator for BWEC.
So far, using ultrasound (or the “acoustic scarecrow device,” as researchers call it), seems promising. In the laboratory, bats avoided the area in which the device was activated, even if food was available.
“The sound is uncomfortable—it would be like us trying to have a conversation with a jumbo jet taking off 10 feet away,” says Arnett.
Last summer, Joe Szewczak, an acoustic expert at Humboldt State University, tested the instrument outside, using infrared videography to track bats at ponds where they regularly forage. He saw a 50-percent decrease in bat activity when the device was activated. This year, he’s testing the device on successive nights to see if fewer bats enter the area over time. “We think they’ll learn to avoid the space altogether,” he says.
Members of the wind industry are cautiously optimistic about the instrument.
“The deterrent has shown some early promise, but they’ve still got quite a bit of work to do,” says AWEA spokesperson Laurie Jodziewicz.
The project’s major challenge will be transmitting the sound far enough, says Tom Kunz, a biologist at Boston University who is involved in the New York arm of the study. While lower sounds, like the rumble of a train, can be heard from miles away, higher-frequency sounds attenuate more quickly. That’s problematic because turbines can be as tall as a 40-story building, and the spinning blades can have a diameter comparable to that of a 747 airplane.
“My own personal view is that it won’t work,” Kunz says. “If we find that it does work, that’s great. If it doesn’t work, then we’re back to square one.”
Meanwhile, scientists are attempting to figure out where, when, how, and why bats are dying.
“In an ideal world, we’d be able to identify sites ahead of time and say ‘This site would be likely to have the least bat mortalities,’” says Hayes. “We’re not there yet, but we’re beginning to understand.”
Nobody knows for certain why bats are killed at wind farms, but scientists recently came up with 11 hypotheses (Frontiers in Ecology and the Environment 5, 315–324; 2007).
1. Linear corridor hypothesis: Wind energy facilities constructed along forested ridgetops create clearings with linear landscapes that are attractive to bats.
2. Roost attraction hypothesis: Wind turbines attract bats because they are perceived as potential roosts.
3. Landscape attraction hypothesis: Bats feed on insects that are attracted to the altered landscapes that commonly surround wind turbines.
4. Low wind velocity hypothesis: Fatalities of feeding and migrating bats are highest during periods of low wind velocity.
5. Heat attraction hypothesis: Flying insects upon which bats feed are attracted to the heat produced by nacelles of wind turbines.
6. Acoustic attraction hypothesis: Bats are attracted to audible and/or ultrasonic sound produced by wind turbines.
7. Visual attraction hypothesis: Nocturnal insects are visually attracted to wind turbines.
8. Echolocation failure hypothesis: Bats cannot acoustically detect moving turbine blades or miscalculate rotor velocity.
9. Electromagnetic field disorientation hypothesis: Wind turbines produce complex electromagnetic fields, causing bats to become disoriented.
10. Decompression hypothesis: Rapid pressure changes cause internal injuries and/or disorient bats while foraging or migrating in proximity to wind turbines.
11. Thermal inversion hypothesis: Thermal inversions create dense fog in cool valleys, concentrating both bats and insects on ridgetops.
By Alisa Opar
6 August 2007
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