Quiet, Please: How Human Noise Affects Wild Places

People better at birding by ear than by eye can find it maddening to try to hear songs and calls over traffic noise. We wait for the bird to raise its voice once the rattling trucks have passed--only to discover that someone has fired up a leafblower nearby, drowning out everything the way radio static drowns out music.

As annoying as unwanted human noise is to us, it's devastating to other creatures. For example: if birds can't hear one another, they can't alert one another to approaching danger or attractive mates or good food sources. Prey animals can't hear predators in a noisy environment, which means more of them get eaten, affecting the ecological balance. Human noise pollution affects plant reproduction by scaring away birds that help distribute seeds, according to a recent paper in the Proceedings of the Royal Society of London B.

Rachel Buxton, an acoustic ecologist at Colorado State University, succinctly explains the essential problem with noise: “It really doesn’t have any boundaries.” Buxton and her colleagues reported recently in the journal Science that noise from humans at least doubles the background sound levels in most protected areas in the United States. “When we think about wilderness, we think about...going to see outstanding scenery,” says co-author Megan McKenna. “We really should think about soundscapes, too.”

Buxton and McKenna and their team used a model for predicting noise based on sound measurements taken all over the country by the National Park Service. Individual scientists hiked in to more than 400 listening stations to set up the equipment, each of which included a sound level meter and a recorder. Each recorder ran for 30 days, collecting every sound. The recordings were then analyzed by acoustic specialists. The researchers then constructed a model for predicting noise by figuring out which sounds were associated with geographic features such as elevation, annual rainfall, proximity to cities, highways and flight paths. By subtracting out natural sound sources, the scientists estimated the amount of noise pollution for each specific wilderness area.

The findings were mixed. Protected areas did show much lower levels of human-caused sound than the "buffer zones” of unprotected land near them, suggesting that these buffer zones really do insulate parks. But 63 percent of the protected areas showed an increase in sound levels of at least three decibels caused by noise pollution. Since decibels are logarithmic, three decibels indicates a doubling of background noise. More than a fifth of protected areas experienced 10 extra decibels of human noise. Sadly, the majority of areas considered “critical habitat” for endangered species were among the regions that dealt with the worst noise.

McKenna said that parks are taking steps to reduce human sounds, such as implementing shuttle systems to reduce the number of cars and posting library-style “quiet” signs. But the problem of pervasive traffic sound—all those low-frequency rumbles from ground and air—is not so easily solved. Buxton suggests that parks look into “quiet pavement” to muffle the sounds of rolling tires and establish noise corridors to align airplane flight paths with highways.

We here are Talkin' Birds plan to drive as little as possible in protected areas, opting instead for quieter transportation such as foot and bicycle. We'll try to keep our voices down, too. And we would never dream of playing a radio in the wilderness, not even to listen to our own show. We would rather not disturb the symphony of life around us, nor its musicians. 

Want to listen to a news story on this research? Click here for a piece from NPR's Morning Edition