Human-Induced Noise Stresses Birds

Exposure to constant noise from oil and gas operations is causing chronic stress in birds. In some cases, the birds also have chicks whose growth is stunted, leading to warnings that bird populations could decline due to human-induced noise pollution.

Image: By Doug Janson (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Birds exposed to constant noise from oil and gas operations show physiological signs of chronic stress and, in some cases, have chicks whose growth is stunted, according to new research. The authors say the findings add to a growing body of evidence suggesting noise pollution from human activity is harmful to wildlife. They also shed light on how stress from chronic noise exposure may impact humans.

In addition, the study, published in the Proceedings of the National Academy of Sciences, found that western bluebirds, which tend to gravitate toward noisy environments, lay fewer eggs that hatch when they nest there.

“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. Surprisingly, we also found that the species we assumed to be most tolerant to noise had the most negative effects,” said lead author Nathan Kleist, from the University of Colorado.

For the study, the researchers followed three species of cavity nesting birds, including western and mountain bluebirds and ash-throated flycatchers, which breed near oil and gas operations on Bureau of Land Management property in New Mexico. The team erected 240 nest boxes on 12 pairs of sites. For three breeding seasons, they took blood samples from adult females and their offspring to assess hatching success, nestling body size and feather length. Across all species and life stages, the birds nesting in areas with more noise had lower baseline levels of a key stress hormone called corticosterone.

“You might assume this means they are not stressed. But what we are learning from both human and rodent research is that with inescapable stressors, including posttraumatic stress disorder (PTSD) in humans, stress hormones are often chronically low,” said co-author Christopher Lowry.

He notes that when the fight-or-flight response is constantly revved, the body sometimes adapts to save energy and can become sensitised. This is called ‘hypocorticism,” and has been linked to inflammation and reduced weight gain in rodents.

Kleist also found that nestlings in noisy areas had a hair-trigger response to the acute stress of being held for 10 minutes, producing more stress hormones than those bred in quiet nests.

“Whether stress hormone levels are high or low, any kind of dysregulation can be bad for a species. In this study, we were able to demonstrate that dysregulation due to noise has reproductive consequences,” explains senior author Clinton Francis.

Chicks in both the quietest and loudest areas had reduced feather growth and body size. The researchers hypothesise that adults in the quietest areas are exposed to more predators, so have less time to forage, and therefore less food for their young. Yet in the loudest areas, the machinery noise masks calls from other birds, a signal of whether predators are present, stressing both mother birds and nestlings.

None of the species studied are endangered. But the researchers suspect that if other species experience similar effects in noisy areas, avian populations could decline as human-caused noise increases.

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