Last fall, a team of researchers from Idaho's Boise State University hiked into the mountains outside of town with backpacks full of batteries and speakers. The unusual cargo was not for a backcountry dance party, but rather for a unique experiment to determine the impact of road noise on migratory birds.
The scientists hung speakers from trees and blasted sounds of cars passing, creating a “phantom road.” They blared the road noise for four days, turned it off for four days, then repeated the cycle. The experiment took place as yellow warblers, ruby-crowned kinglets, American robins and other birds passed through on their journey south, its conclusions were striking: On the days when the road was “on,” bird abundance declined by more 25 percent, and two species, cedar waxwings and yellow warblers, avoided the area almost entirely.
In other words, the researchers found that anthropogenic noise alone can reduce the amount of stopover habitat available to migratory birds. And because 83 percent of the land area in the U.S. is within one kilometer of a road, they wrote, “it is likely that noise-sensitive species such as the yellow warbler avoid substantial areas of otherwise suitable habitat simply because they are too loud.”
How bad can noise really be? It's a question that researchers in the burgeoning field of soundscape ecology are constantly asking. And their growing body of research is starting to show that the noises humans and our machines make can have significant and widespread effects on animals. For example:
- Bernie Krause, who began recording wild soundscapes 45 years ago, documented the effect of low-flying Navy jets on the chorusing of spadefoot toads in California’s Mono Lake. The toads, which normally sing in a synchronized rhythm that makes it hard for predators to pick off individuals, took 45 minutes to reestablish their singing pattern after a jet passed overhead.
- In 2012, researchers at University of Copenhagen and Aberystwyth University found that some songbirds in urban areas not only sing at a higher pitch to overcome the low-frequency din of city noise, but adjust their songs to account for urban architecture as well. Larger birds like mourning doves, which sing at low pitches, are more affected by manmade noise than smaller, higher-pitched birds like house finches, found researcher Clint Francis.
- Underwater sonar from British naval ships has been linked to the widespread stranding of dolphins.
Anthropogenic noise can even impact plants: In a 2012 study, Francis found fewer piñon pine seedlings around noisy natural gas compressors in New Mexico. Why? Scrub jays, voracious consumers and distributors of piñon seeds, are put off by the noise and avoid the area.
“The world’s getting louder and there’s a lot of evidence already that it’s having an impact on wildlife,” says Jesse Barber, a biology professor at Boise State who co-authored the phantom road paper. “We need to understand noise so we can mitigate it.”
Barber’s study, which came out in October, is already having an impact in the National Park Service, which funded the study. The NPS’s Natural Sounds and Night Skies division is now looking for a park road to re-surface with “quiet pavement,” which can reduce road noise by a factor of ten. “We know noise is a stressor with significant effects,” says Kurt Fristrup, a senior scientist in the division. But making an area quieter is a lot harder than making it louder.
Still, there are solutions at hand: In addition to quiet pavement, government agencies can erect sound walls around gas compressors and highways, lower speed limits, or build fewer roads. Making the world quieter has another benefit, too: By reducing noise stress on birds and other animals, we can help them be in better shape to confront more vexing problems like climate change.
“Problems like climate change are truly in the hands of the politicians,” says Barber. “Road noise is a much more tractable problem. We have engineering solutions to make the world quieter and they can be immediately implemented.”
Emily Guerin is a correspondent for High Country News. She tweets @guerinemily.