Industrial noise may alter bluebird behavior but not cognitive ability

UNIVERSITY PARK, Pa. — Scientists have long wondered whether loud, human-caused noise interferes with wild animals’ cognition — their ability to think and learn — by causing stress, distraction or making it harder for them to focus. The results of a novel study of Eastern bluebirds conducted by a team of researchers at Penn State suggests that, at least in some cases, short-term noise doesn’t affect them much.

In findings published in Behavioral Ecology, the researchers reported that bluebirds exposed to 48 hours of continuous sounds from a natural gas pipeline compressor station were able to solve a problem, learn a task and access their nest boxes about as well as bluebirds that were not subjected to the noise and experienced normal, quiet conditions.

“We were particularly interested in bluebirds because they are actually doing really, really well, and that's because of humans putting up nest boxes for them,” said team leader and senior author Jason Keagy, associate research professor of wildlife behavioral ecology in the College of Agricultural Sciences. “Bluebirds typically are not thought of as being smart birds, like crows or chickadees, but this research definitely is relevant because bluebirds like the edge habitats that pipelines create.”

The experiment involved 44 Eastern bluebirds, with 22 exposed to noise and 22 not subjected to noise. All the birds were caring for nestlings, so they were highly motivated to visit their nests. The researchers attached a small operant conditioning device — a controlled laboratory sfor one hour. The device had one active — correct — lever and one inactive — incorrect — lever. To reach their chicks, the parent had to land on the correct lever.

The researchers measured cognitive performance by how quickly birds learned which lever was correct and whether they improved over time; behavior, measured by how often they fed their chicks; and how long they hesitated before approaching the nest, a metric they called “approach latency.” The team also recorded reproductive outcomes, monitoring nestling health and whether chicks successfully fledged.

The team found that birds exposed to noise learned the task and solved the problem to access their next boxes about as well as birds in quiet conditions. Noise exposure over 48 hours did not impair learning or problem solving, according to study first author Sara Isgate, who graduated from Penn State with a master’s degree in wildlife and fisheries science, with a minor in forestry. She is now a doctoral degree student at Indiana University, Bloomington.

“The birds learned the task, and problem-solving time significantly decreased over the trials, as birds repeated the task, they solved it faster and faster — that’s classic evidence of learning,” she said. “However, noise did change some behaviors.”

Isgate explained that feeding behavior was altered. In quiet conditions, both males and females fed chicks a little less over the two days. Under noise, females reduced feeding even more and males appeared to compensate by feeding more. So, noise may have shifted parental responsibilities rather than reducing total care.

Also, bluebirds subjected to noise appeared to be more cautious about approaching their nests, Isgate said. Control birds in quiet conditions became more comfortable and approached next boxes faster over time, while noise-exposed birds became slower to approach over time. This suggests the birds were disturbed by the noise, even though they could still solve the task, Isgate noted. But noise or not, the nestlings did fine. The researchers did not find evidence that the short-term noise exposure impacted chick health.

The nest boxes were placed at Penn State’s Russell E. Larson Agricultural Research Center. For the noise pollution treatment, the researchers randomly played five one-hour recordings that were taken at various times and weather conditions at a natural gas compressor station using high-quality microphones. They used ATV speakers with portable electronic devices that store and play digital audio files to generate noise over the course of two days, powered by 12-volt marine deep-cycle batteries.

“This research suggests that wild animals may sometimes cope better than expected, especially when they're highly motivated by the need to feed their offspring — at least during short-term noise exposure,” Keagy said. “Despite being exposed to a realistic industrial noise source, the birds maintained their ability to learn and solve the problem. The noise changed some behaviors, but not the measured cognitive ability itself.”

Contributing to the research were Julian Avery, associate research professor in wildlife ecology and conservation; Caitlin Honus, undergraduate researcher who graduated with a degree in animal science with a dual minor in biology and wildlife and fisheries science; Gabriel Casanova, undergraduate research assistant majoring in veterinary and biomedical sciences; and Bailey Betcher, undergraduate research assistant majoring in wildlife and fisheries science.

The research was funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture under project number PEN04768 and accession number 1026660, the Pennsylvania Society for Ornithology and Penn State. This content is solely the responsibility of the authors and does not necessarily represent the views of the funders.