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U.S.A.? More like U.S. of a deafening cacophony of anthropogenic noise. According to research presented at last month’s annual American Association for the Advancement of Science, sound pollution has more than doubled over the last three decades and it’s bleeding into the most sacred of sites: our national parks. That news is bad enough for Americans hoping to escape the din of urban life, but it’s downright threatening to the birds that reside there.
Consider that one aircraft can generate buzz audible up to 25 miles from its flight path, and a loud vehicle is heard up to six miles from the road. Now consider the approximately 87,000 flights that take off in the U.S. every day and the countless cars clattering down American highways, freeways, backstreets and country roads.
It all amounts to this map, which illustrates noise pollution across the country, thanks to 10 years of research focused on 600 listening sites inside the park system and 200 sites in urban areas:
Sure, it looks bad, but it sounds worse—a recent study of 308 populations of 183 bird species across North America, Europe and the Caribbean found that manmade noise interferes with birds’ abilities to "receive, respond to and dispatch acoustic clues and signals." This is likely why birds avoid loud areas, according the study author Clinton Francis, assistant professor of biology at California Polytechnic State University, San Luis Obispo.
Birds of prey are most affected because they rely on sound to hunt, but an acoustic environment marred by manmade cacophony can make it hard for all kinds of birds to communicate with each other and to detect predators. (Not all species despise a din, though: Hummingbirds, for instance, appear to favor loud environments over quiet ones.)
The upside: Unlike air or water contamination, noise pollution can be rectified almost immediately, says Kurt Fristrup, a senior scientist for the National Park Service's Natural Sounds and Night Skies Division who helped create the sound map.
“We have the potential to make things right right away if we just make better choices,” he says. The park service is is already exploring fixes. For example, just one flight path now crosses over Colorado’s Rocky Mountain National Park en route to Denver’s airport, down from three.
This summer, NPS will begin another experiment: resurfacing some park roads with “quiet pavement” that has been shown to reduce traffic sound levels by 10 decibels—the sonic equivalent of decreasing the number of cars on that road by an order of 10.
Once they’re installed, Fristrup and his colleagues will study the nearby habitat to see how the birds respond to their newly serene home.