noise

Birds, Like People, Suffer from Loud Noise

Debbie Blicher is Senior Producer of Ray Brown's Talkin' Birds.

A new study in Proceedings of the National Academy of Sciences indicates that birds respond like humans do when exposed to constant loud noise. Researchers found that adults and nestlings of three species in the wild showed signs of chronic stress caused by human noise pollution. 

Most birds exposed to constant loud noise will simply leave an area; this study looked at what happens to the birds that stay. Lead author Nathan Kleist conducted the research while a Ph.D student in evolutionary biology at the University of Colorado-Boulder, along with co-author Rob Guralnick, associate curator of biodiversity informatics at the Florida Museum of Natural History.

The research team, led by Kleist, set up 240 nesting boxes at three specific distances from gas compressors on property in New Mexico. The team tested levels of the stress hormone corticosterone in three species: Western Bluebird, Mountain Bluebird, and Ash-throated Flycatcher. The researchers found that the louder the noise from the gas compressors, the lower the birds’ baseline corticosterone levels in all three species.

Christopher Lowry, study co-author and stress physiologist at CU Boulder, explains: Although it seems odd that the corticosteroid levels would be low, lab studies of chronic stress in humans have shown that low corticosterone can signal stress so intense that the body has to reduce baseline levels of the hormone to protect itself (so that there's room for it to shoot up if needed). In fact, when these birds experienced sudden stress, their corticosteroid shot up high and came down only very slowly, like it does in chronically stressed humans.

In the noisiest environments—the ones closest to the compressors—nestlings had smaller body size and reduced feather development. In Western Bluebirds, the species that showed the greatest noise tolerance, fewer eggs hatched than expected.

“These birds can’t escape this noise," says Guralnick. "It’s persistent, and it completely screws up their ability to get cues from the environment." For example, adults rearing chicks can't tell whether it's safe to leave the nest for food. Guralnick explains, "Just as constant stress tends to degrade many aspects of a person’s health, this ultimately has a whole cascade of effects on their physiological health and fitness.” 

Since noise at natural gas fields is not unusually loud compared with human noise in many other parts of the country, this study has implications for protecting wildlife and even human health. The researchers suspect that if other species react the way these species did, bird populations could decline if we humans become noisier.

“This study shows that noise pollution reduces animal habitat and directly influences their fitness and ultimately their numbers,” Guralnick said. “By doing so, it makes it harder for animals to survive. Taken together, that’s a pretty damning picture of what human-made noise can do to natural populations of animals.”

Quiet, Please: How Human Noise Affects Wild Places

Debbie Blicher is Senior Producer of Ray Brown's Talkin' Birds.

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