Like pedestrians swiping through their smartphones, flying birds don’t always look at what’s ahead. Unlike us, though, they have a good excuse: They’re usually scanning the ground for landmarks to help them navigate. But thanks to all the structures we've put in their way, looking down can lead birds to their doom. Collisions with buildings, towers, and turbines kill more than a billion birds a year, experts say.
Just as a honking car warns you to glance up from Twitter and not step into traffic, ecologist John Swaddle thinks attention-grabbing sounds may stop birds from crashing into manmade structures—or at least slow them down enough to save their lives. He wants to use directional speakers to aim columns of sound at birds as they approach buildings and other hazards, alerting them to obstacles in their path. He calls the idea “the acoustic lighthouse.”
While the technology isn’t ready for the real world yet, Swaddle is encouraged by early lab trials with Zebra Finches, the results of which can be found in Integrative and Comparative Biology. “What we’ve published is a first step that shows the general concept could work,” says Swaddle, a professor at the College of William and Mary. “Everything we’ve observed so far seems promising.”
To test the acoustic lighthouse, Swaddle and graduate student Nicole Ingrassia trained 18 finches to fly down a corridor 28 feet long. About eight feet from the end, they placed a floor-to-ceiling wooden frame not quite as wide as the corridor. At first the frame was left empty so birds could pass freely through it. But after a few basic runs, things got tricky. For some flights the frame was covered with a mist net—a soft stand-in for a building facade. Other times, a small speaker stationed half a meter in front of the vacant frame blasted the birds with pink noise, which is like white noise, but heavier on the bass. The final setup included both the mist net and the speaker.
Swaddle and Ingrassia recorded the birds’ reactions during each trial on a high-speed video camera. The film showed that sound alone didn't seem to change the finches' flight, but when only the net was applied, the birds would see the obstruction and slow down. When the objects were combined, the subjects slowed down 20 percent more than with just the net, and two of them even avoided the net altogether. “I think what’s happening is the sound is not an inherent deterrent by itself,” Swaddle says. “What it’s doing, we think, is drawing attention to what’s in front of the bird.”
Along with putting on the brakes, finches that heard the pink noise before hitting the net also adjusted their angle of flight in a way that could save their lives in a real collision. “Their bodies went from basically a head-on, horizontal collision to almost like a 45-degree-angle position with the head up, like when they make a landing,” Swaddle says. “So even if there is a collision, this indicates it’s less likely to be fatal.”
The big question now is whether birds in the wild will respond the same way over the long term. Daniel Klem Jr., a professor with the Acopian Center for Ornithology at Muhlenberg College, says he finds Swaddle’s research “interesting and potentially of value,” even though he has long been skeptical of sound as a tool for changing bird behavior. He says previous attempts to keep birds away with noise—to stop them from raiding farms or giving cars on dealership lots an unwanted paint job—have proven largely unsuccessful.
Such skepticism is understandable, Swaddle says. Unless there’s a direct threat associated with the sound, birds tend to just get used to it. But if individuals learn to associate a specific noise with the very real danger of hitting an unyielding object, it may become a stronger deterrent over time. Swaddle applied a similar idea to one of his previous inventions, which uses pink noise to drive birds away from airports, crop fields, and other places where they might roost or forage. Rather than a false alarm the birds would eventually learn to ignore, his "sonic net" drowns out their ability to communicate with one another. Unable to hear each other's warnings about incoming predators, the birds leave the area, apparently feeling unsafe.
Swaddle says he’s filed initial patent paperwork for the acoustic lighthouse and is seeking grants for field trials with a variety of bird species. The real-world application of his concept would involve larger speakers that project roughly 80 decibels of sound—about as loud as a garbage disposal if you're standing next to it—dozens of feet in front of structures. He also plans to remix tracks that can be heard above traffic and other human commotion.
Installing the deterrent on wind turbines, cell towers, and other isolated structures would be fairly easy. Cities, on the other hand, are a challenge, Swaddle says. Directional speakers could be mounted on upper floors of skyscrapers in a way that doesn’t bother people indoors or on the street, but will be more difficult to warn birds away from short buildings without adding to the ever-present din.
More importantly, Swaddle first needs to build a market for the technology. There’s a strong incentive for wind-energy companies to adopt it; taking steps to mitigate bird deaths can help them win approval for new projects and avoid hefty fines, he says. He’s also spoken with building managers who are genuinely troubled by bird collisions, and is hoping to connect with sustainably minded corporations.
Whether it’s out of concern for birds or simply in a business’s best interests, “we should all be interested in stopping the unintended killing we’re involved with,” Klem says. He’s been studying bird deaths from window collisions since the 1970s, and has yet to see a good solution. Even if the acoustic lighthouse isn't the perfect fix, it at least has the potential to make some noise around an underappreciated problem.
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