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Birds on the Neighborhood Watch

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New research shows that birds can set off a chain reaction of early-warning calls about predators that protect other birds and even mammals.

by Xochitl Rojas-Rocha

May 20, 2015—The birds of the forest have evolved their own version of the neighborhood watch, reports The New York Times. One of the forest’s most vocal birds, the black-capped chickadee (pictured above), is known for fearlessly “mobbing” predators. Chickadees often surround and harass a hawk with their strident chick-a-dee call until it leaves. Now, studies suggest that chickadees and other songbirds may alert other bird species and even mammals to danger.

Erick Greene, a professor of biology at the University of Montana, spearheaded one study that examines this unexpected alliance. Greene has always been a “total nature nerd,” he told The New York Times. Sound in particular allured him while he was young — he loved everything from birdsong to classical and Renaissance music. Nowadays, that allure drives him to traverse the forest asking questions like, What are these birds saying to each other?

Greene analyzes changes in birds’ calls before and after a predator’s appearance. He’s taken a more innovative approach than waiting for a hawk or an owl to appear in an area: the “roboraptor.” Taxidermist Eugene Streekstra helps Greene by outfitting taxidermied owls and other bird predators with robotic parts like swiveling heads. Greene places the covered decoy in an area thick with songbirds, waits for the opportune moment to unveil it and records the chaos that ensues.

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While other scientists have also made progress in studying songbirds’ alarm calls, Greene’s research is unique in its scope, says Jesse Barber, an assistant professor and expert on animal acoustics at Boise State University. Greene’s research looks at the effects of birds’ warning calls “across large swaths of habitat, and this is really where the field has yet to go,” Barber told The New York Times.

Previous research in the field has yielded all sorts of interesting findings about how birds communicate. Scientists believed that birds gave off warning calls to alert their fellows nearby. But a previous study of Greene’s suggests that the warnings spread from bird to bird for greater distances, like a rumor or game of telephone, sometimes traveling through the forest at great than 100 miles per hour. Because raptors don’t hear well at frequencies between six and 10 kilohertz, they aren’t privy to the high-pitched alarm calls spreading ahead of them. “So it’s sort of a private channel,” says Greene. This gives the songbirds precious minutes to dive for cover before death passes overhead on silent wings.

Greene’s previous studies have also found that mammals like squirrels can pick UP birds’ warning calls. When a bird shrieks its shrill warning cry, the squirrel gives its own alarm call, which sounds very similar to the songbird’s. Conversely, when the squirrel spots the predator first, the songbird takes up the call initiated by the squirrel.

Scientists hope that the results from studies like Greene’s will help us understand how increasing noise pollution from roads and cities affects songbirds. In 2013, Barber conducted a study by placing speakers throughout the forest to mimic the noise generated by a busy road. Because birds have to allocate time between feeding and staying on the lookout for predators, the birds in the noisy area grew physically weaker. Increased levels of background noise may force birds to spend more time actively listening for alarm calls — and this could take away significantly from the time they spend foraging.

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In his book, published in 2012, Jon Young writes that we can learn to understand "bird language," and shows how that can enable us to know when other animals -- including predators -- are around. "Deep bird language is an ancient discipline, perfected by Native peoples the world over. Finally, science is catching up. . ." Truer today than when he wrote those words.