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.”