Western bluebirds are experiencing chronic stress due to industrial noise from oil and gas operations. Noise pollution, according to a study, is causing post-traumatic stress disorder-like symptoms in birds and has stunted the growth of their nestlings.

Exposure to constant noise pollution has affected the growth of chicks and the quantity of hatched eggs in bluebirds. The research observed other symptoms that are surprisingly similar to PTSD in humans.

Chronic Stress Affects Health Of Birds

Even western bluebirds that are known for their natural tendency to move toward noisy places were found to lay fewer eggs that hatch when their nesting environment is located near the source of the noise pollution.

"In what we consider to be the most integrated study of the effects of noise pollution on birds to date, we found that it can significantly impact both their stress hormones and their fitness," says Nathan Kleist, lead author of the study. Kleist and his team conducted the field research from 2010 to 2014.

When Bluebirds Can't Sing

The researchers investigated several breeding seasons of bluebirds that are nesting 75 yards from a gas compressor on the Bureau of Land and Management's Rattlesnake Canyon Habitat Management Area in New Mexico.

Machinery from the oil and gas operations causes nonstop whining noises that were proved to have distressing effects on birds.

Kleist's crew built 240 nesting boxes across a dozen of sites for cavity-nesting bluebirds and observed the hatching patterns of adult bluebirds and monitored the feather length and body size of nestlings.

Stressful Condition May Affect Bird Reproduction

The researchers also tested the corticosterone levels in the blood of three species of bluebirds - western bluebirds, mountain bluebirds, and ash-throated flycatchers.

Corticosterone is the bird equivalent of cortisol, a major stress hormone in animals that is responsible for regulating certain functions, including the response to stress.

The study revealed that the chicks and female adult bluebirds exposed to constant loud noise have lower than normal baseline corticosterone levels.

"On the surface, you might look at this result and assume this means they are not stressed. But what we are learning from both human and rodent research is that with inescapable stressors, including post-traumatic stress disorder in humans, stress hormones are often chronically low," says Christopher Lowry, stress physiologist at the University of Colorado Boulder and coauthor of the study.

Humans suffering from PTSD and chronic fatigue syndrome react to chronic stress by muting the hypothalamic-pituitary-adrenal axis. When this happens, the overall health is affected, leading to other conditions such as cardiovascular problems, gastrointestinal issues, and extreme fatigue.

Researchers observed that the bluebirds in the tested area had reduced feather growth and smaller body size. Nestlings also had hair-trigger response when held by humans for 10 minutes. These symptoms could diminish their chance of survival.

The research was funded by the National Geographic Society, the National Science Foundation, the North American Bluebird Society, and the University of Colorado Graduate School.

Results of the study was recently published by the Proceedings of the National Academy of Sciences.

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