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　　It's hard to be a bird in our human-dominated world.

　　You can barely hear yourself sing, let alone hear the songs of your friends... and you can forget about hearing a predator. Noise is almost everywhere. Especially noise from traffic. A whopping 83 percent of the surface of the continental U.S. is within just one kilometer of a road.

　　Researchers have tried to assess the impact of road noise on animals by, understandably, looking at animals living near noisy roads. The problem is that noisy roads are both noisy, and well, they're roads. It's hard to separate the two.

　　"And so we figured out a way to have just the noise without any of the other effects of the road, and to do that we ran speakers through a forest where there was no road."

　　Chris McClure, a biologist at Boise State University and The Peregrine Fund. He and his team built their audio phantom road at a popular stopover site for birds in Idaho as they fly south for the winter.

　　While the noise kept lots of birds away, some stuck around. But they had trouble putting on enough weight to fuel the next leg of their migratory journey.

　　"They have to fatten up but they also have to not get eaten by a predator. And those two things are in conflict. Because to eat, they have to look down, which means they aren't looking at predators."

　　And when it's too loud, they can't hear the alarm calls of other birds. So they have to waste time looking for predators instead of foraging. The study is in the journal Animal Conservation.

　　By 2050, it's thought that enough new roads will be built to circle the planet more than 600 times. But there's an easy solution to the noise problem.

　　"Lowering speed limits does a lot."

　　So next time you're driving through nature, just slow down a little. It's safer for you and the wildlife. And you can enjoy the view a little longer.

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