Noise pollution is causing birds extreme amounts of stress
Researchers have found that constant noise pollution could be causing extreme stress to bird populations around the world.

Joseph Scalise | Apr 19, 2018

Human-triggered noise pollution may be causing birds extreme amounts of stress, according to new research in the Proceedings of the National Academy of Sciences.

This finding comes from scientists at multiple U.S. universities, who discovered that adults and nestlings from three different bird species showed multiple signs of chronic stress linked to noise pollution. That included skewed stress hormone levels that may be the result of increased anxiety, distraction, and hypervigilance.

Researchers discovered that constant noise could be acting as an "acoustic blanket" that muffles the audio cues birds use to detect predators and objects in their environment. As they cannot tell if their surroundings are safe, mother birds need to choose between staying to protect their young at the nest and going out to find food.

The data showed that nestlings from nosy environments tend to have small body sizes and reduced feather development. In addition, some species also showed large declines in hatching rates as a result of noise.

"These birds can't escape this noise. It's persistent, and it completely screws up their ability to get cues from the environment," said study co-author Rob Guralnick, associate curator of biodiversity informatics at the Florida Museum of Natural History, according to Phys.org."They're perpetually stressed because they can't figure out what's going on."

The team in the study set up 240 nesting boxes staggered at precise distances from loud gas compressors and then recorded nesting bird's stress responses in relation to different noise levels.

Once they recorded that information, the scientists tested levels of the stress hormone corticosterone in three bird species: western bluebirds, mountain bluebirds, and ash-throated flycatchers. While researchers expected to see high corticosterone levels, they found the noise from gas compressors lowered the birds' baseline corticosterone levels.

To explain that trend, researchers compared their results to lab studies on chronic stress. That showed low corticosterone can be a sign of stress that is so intense the body dials down baseline levels of the hormone as a means of self-protection.When the scientists tested how chicks responded to sudden threats, they discovered that the birds' corticosterone skyrocketed compared with typical high-stress levels. The chicks also took a long time to return to baseline levels.

The study is the first to test the relationships between noise, stress hormones, and fitness in animals that breed in natural areas with unrelenting, human-made noise. It also sheds new light on how noise affects wildlife and reveals that such pollution reduces animal habitat and makes it harder for them to survive.

Researchers hope the new information will help scientists gain a better understanding of noise pollution in relation to different animal populations.

"Hearing is the universal surveillance system across vertebrates, including humans," said study co-author Clinton Francis, assistant professor of biology at California Polytechnic State University, in a statement. "Hearing is also the sense that remains active even during sleep and other instances of unconsciousness. Because we and other animals rely on hearing in these capacities, it may not be too much of a stretch to expect similar physiological impacts on humans."

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