New research suggests that there are some circumstances that could cause birds to have something similar to post-traumatic stress disorder. These specifically include distracting loud noises that could interfere with the health of adult birds and their chicks alike.
In a study published Monday in the journal Proceedings of the National Academy of Sciences, researchers from the University of Colorado at Boulder, California Polytechnic State University, and the Florida Museum of National History discovered that certain bird species are less successful in hatching eggs when they nest in noisy areas like they often do. According to lead author Nathan Kleist, a doctoral student at UC-Boulder at the time the study was conducted, noise pollution could “significantly impact” the fitness and stress hormones of birds, including those that are seemingly used to existing in noisy environments.
“Surprisingly, we also found that the species we assumed to be most tolerant to noise had the most negative effects,” said Kleist, as quoted in a press release on the UC-Boulder website.
A report from the Washington Post provided an example of how birds seem to get PTSD-like symptoms when exposed to noise pollution — a female bluebird who chose to nest about 75 yards away from a natural gas compressor. While the bird didn’t initially seem to be affected by the loud noises from the machinery, she ultimately found it hard to hear approaching predators or even more “normal” noises from her environment. With the bluebird unable to resettle and forced to be to be especially vigilant, that increased her stress levels and affected her health, resulting in chicks who turned out to be “small and scantily feathered, if they survived at all.”
The nesting bluebird in the above example was one of several birds analyzed in the researchers’ study, which covered 240 nesting sites surrounding northern New Mexico’s oil and gas facilities. She also happened to be an example of a bird with physiological symptoms resembling those found in humans with PTSD, the Washington Post added.
“Noise is causing birds to be in a situation where they’re chronically stressed. . . and that has really huge health consequences for birds and their offspring,” said Florida Museum of Natural History associate curator of biodiversity informatics Rob Guralnick.
Although the Washington Post observed that it’s impossible to say that noise pollution causes mental instability in birds, the publication added that the study proved that there is a “clear connection” linking loud noises with higher stress levels and lower survival rates in birds.
“Habitat degradation is always conceived of as clear cutting, or, you know, changing the environment in a physical way,” Guralnick added.
“But this is an acoustic degradation of the environment. We think it is a real conservation concern.”
The researchers studied three separate bird species that breed near New Mexico’s Bureau of Land Management property in the northern part of the state— western bluebirds, mountain bluebirds, and ash-throated flycatchers. In a span of three breeding seasons, the team gathered blood samples from adult female birds and their chicks, and looked at several factors to determine the effects of surrounding noise pollution, including hatching success and the body size and feather length of nestlings.
Regardless of bird species or life stage, the researchers found that the birds nesting in noisier areas were more prone to PTSD-like symptoms, due to lower levels of the stress hormone corticosterone. UC-Boulder stress physiologist and study co-author Christopher Lowry explained that these findings were consistent with what previous research on human and rodent subjects suggested.
“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 post-traumatic stress disorder (PTSD) in humans, stress hormones are often chronically low.”
Interestingly, it was found that feather growth and body size was lowest among chicks in the loudest and quietest nesting areas alike, with a “sweet spot” in areas that had moderate levels of noise. The researchers believe this is the case because adult birds who nest in quiet areas have to deal with more predators, and consequently do not have enough time to forage for food to feed their offspring. Conversely, machinery noise made it hard to hear warning calls from other birds that hinted at the presence of predators in the area. Kleist compared the stress this places on birds to a common human situation – where parents strain to be heard when talking to their friends or children while at a loud party.
Study author Clinton Francis, a professor of biological sciences at Cal Poly, expressed concern that the phenomenon of birds having symptoms consistent with PTSD is particularly concerning for the western bluebird, a species thought to be resilient to noise pollution. Hatching rates have been on the way down for this species, and Francis sees this as proof of an “ecological trap,” where a creature gravitates toward situations or environments that are actually harmful to them. Speaking to the Washington Post, he added that more research may be needed to confirm if there is a “Goldilocks distance” where birds can be relatively unaffected by noise pollution and the threat of predators alike, as predators could also be stressed by loud noises.