Listen. Can you hear the whistle?

No? That’s the point. Only flying mammals can hear it. And it could save their lives. We’re talking about a unique 3D-printed whistle that researchers have designed to warn bats that they are getting too close to deadly wind turbine blades. 

The whistles are designed to mimic the ultrasonic pulses that bats normally use for echolocation. Mounted on wind turbine blades, they could help reduce bat fatalities that have become a problem at wind farms, according to researchers who presented their work recently at the Acoustical Society of America meeting.

Wind turbines are great for clean energy, but they can take a toll on bat populations. About 52,000 wind turbines operate in the United States, and they kill hundreds of thousands of bats, according to estimates from the U.S. Geological Survey. That number will only go up as wind power gains traction. Wind energy generated 6.5 percent of electricity in the United States in 2018, and is expected to grow at least four-fold by 2050.

Researchers have been exploring cost-effective ways to make wind turbines more bat-friendly without affecting their output. One approach is to fend bats away using devices that transmit ultrasonic noise. Researchers at Texas State University together with Bat Conservation International have tested one such system that jams bats’ echolocation. The loudspeakers are mounted at the center of the turbine, and one issue is that the ultrasound waves fade quickly in air and may not reach past the gargantuan blades. Plus the devices need a power source.

Michael Smotherman of Texas A&M University and his colleagues from the University of Massachusetts Amherst designed a simple whistle that mimics the anatomical structures in the bat’s larynx. The whistle produces tones that bats can detect at distances of over 100 meters. The whistle can be 3D-printed and does not need any power. As turbine blades turn, air passes through the whistles mounted on them, creating an ultrasonic noise similar to the bats’ echolocation signals. Bats approaching the turbine should hear the sound and change direction to avoid a collision.

To test the whistle, the researchers played recordings of the sounds they produce in the lab and out in the field to see if bats changed their flight paths. The showed that the bats detect the sound, Smotherman says, but there were species-specific differences, with some bats reflexively steering away while others noticing it but ignoring it.

“The limitation of lab studies is we can’t measure whether the device helps bats avoid hitting blades,” he says. But field studies are challenging because the bats flying high 100 m or more when they interact with turbines. “The ultimate test would be putting them on turbines where lots of bats are routinely killed, [such as] along migration routes for instance, and seeing if it reduces annual mortality,” he says.

But that will not be easy since the turbines are enormous. Plus the researchers will need to try many devices in different locations to accurately assess impact. The US DOE has been very supportive of the endeavor, Smotherman adds, “but it will also ultimately require help from the owners and manufacturers to come to fruition.”

Source: Michael Smotherman et al. Developing a biomimetic acoustic deterrent to reduce bat mortalities at wind turbines. Journal of the Acoustical Society of America, 2019.

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