Even America’s protected areas are being subjected to harmful levels of noise pollution.
If a tree falls in the forest, and there’s no one around, the National Park Service will still hear it.
For the past decade, staff at the NPS have been lugging recording equipment into almost 500 sites around the U.S., in a bid to measure the sounds of the nation’s quietest places. For weeks at a time, sensors measured local noise levels, microphones recorded the actual soundscapes, and weather instruments noted temperature, air pressure, and other factors that affect the travel of sound. Collectively, the NPS recorded almost 1.5 million hours of sound—an extensive archive of bird songs and wolf howls, butting bighorns and tail-slapping beavers, rumbling thunder and rustling foliage.
Rachel Buxton from Colorado State University and her colleagues have now used their bonanza of data to map the extent to which excessive noise permeates American wilderness. The data revealed that a surprising swathe of protected areas are being carpeted by the clamor of human activity. People have doubled the background noise levels in two-thirds of these supposedly pristine zones, and increased noise by 10 times or more in a fifth of them. “If you could have heard something 100 feet away, now you can only hear it 10 feet away,” Buxton says of the latter.
That’s a problem. Over the past two decades, many studies have shown that human-made noise can cause stress, disrupt feeding, drown out mating calls, mask the approach of predators, and suppress the complexity of animal songs. It even affects species without ears: Some plants suffer as seed-dispersing animals are driven away. And in perhaps the most clean-cut demonstration of the harms of noise, one team of scientists set up a “phantom road” in Idaho—recreating the sound of passing traffic through speakers lashed to trees. That half-mile corridor of disembodied sound drove away a third of the local birds, and suppressed the weight of many of the species that stayed.
Noisy wilderness is a problem for people, too. One survey showed that as many people go to natural parks for their serene soundscapes as for their scenic landscapes. They find peace in quiet. For that reason, many scientists believe that noise should be treated as a pollutant—as significant and threatening as toxic chemicals in the water or irritating particles in the air. “Noise pollution doesn’t yet receive the attention other pollutants do,” says Angelika Nelson, from Ohio State University. “Hopefully the analysis in this new paper will help to increase people’s awareness of the effects it can have on us and other organisms, and change how we think about protected areas.”
In fairness, the NPS has long cared about sound*. The Organic Act of 1916, which created the agency, charged it to “conserve the scenery and the national and historic objects and the wild life therein”, which subsequent policies took to include “natural soundscapes.” A few later acts, all meant to address the problem of noisy aircraft flying overhead pristine quiet, led to the creation of the agency’s Natural Sounds and Night Skies Division—the group responsible for the hard-won recordings that Buxton used…
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