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.
Working with NPS engineers, her team used the assembled data to predict sound levels all over the U.S., taking account of factors like roads, aircraft routes, climate differences, tree cover, nearby rivers, and more. They also predicted what those levels would be like if humans weren’t around, to pinpoint the regions where our influence contributes to the greatest ruckus.
The team found that protected spaces are indeed quieter than unprotected ones, but many are still unacceptably noisy, including regions that are havens for endangered species. Around 58 percent of the areas had sound levels that were twice the natural baselines, and 14 percent had levels that were ten times higher. Even wilderness areas—remote and heavily protected regions that, by definition, are “untrammelled by man”—aren’t immune. Most of these were expectedly tranquil, but around 12 percent had sound levels that were twice the natural baselines.
“The biggest culprits by far were aircraft and vehicle noise,” says Buxton. Industrial land use was also a problem, including mining, forestry, and oil and gas extraction. And some sites, like Rock Creek Park and the National Mall in Washington, D.C. were inundated by the clamor of crowds.