Sounds of Traffic Stress Most Migrating Birds, Study Finds

By Gabrielle Jonas on November 8, 2013 9:55 AM EST

This Yellow Warbler Couldn't Stand The Sounds of Cars in National Parks
This migrating bird avoided the recorded sounds of traffic, even though they were coming from speakers nowhere near an actual road. (Photo: Ashley Jensen)

In a study that highlights the effects traffic has on wildlife, ornithologists Wednesday proved that migrating birds avoid the sound of traffic noise. The study,which appeared in the latest issue of Proceedings of the Royal Society B, is the first one  to look at migrating birds and traffic noise; and to separate out other potential traffic turnoffs such as pollution and the size and speed of the car itself.

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To rule out these other factors, Dr. Chris McClure and his colleagues at the Department of Biological Sciences, Boise State University, set up a 0.5 km (0.31 mile) long phantom road in the middle of nowhere. They erected 15 pairs of speakers in Douglas Fir trees above the crest of a ridge in the Boise Foothills of Southern Idaho. They oriented half the speakers towards an evergreen forest; the other towards a thicket  of cherry bushes and sagebrush.

The speakers played recordings of traffic noise on roads for four days during regular traffic hours. Each four-day period was followed by a four-day off period. The ornithologists compared how often birds visited the cherry bushes during the noisy and quiet periods of their autumn migration.

The ornithologists had recorded traffic levels and speeds found along roads in some of the most visited national parks, national forests and other protected areas globally, demonstrating that even nature preserves can unwittingly threaten the welfare of birds and animals by allowing light traffic.  

When the traffic noise was playing, 13 of 22 of the bird species stayed away. The number of individual birds, regardless of species, present along the phantom road during noise-on periods was 28% less than when it was off. Cedar Waxwing and Yellow Warbler almost completely avoided the phantom road during noisy periods. Eight species seemed unaffected by it, and one-the Cassin's Finch-actually preferred the area with the noise.

Even the birds who brave traffic noise pay dearly for that choice. Noisy areas mask the sounds of predators or the warning call from other birds, having a foraging bird looking anxiously looking around rather than eating more. Such behaviors can quickly translate into lower weight, a life-threatening condition when migrating all the way to South America, for instance. "There's quite a cost for putting up with it," Dr. McClure said.

The cost of putting up with it is the subject of part two of the study, to be published next year. Dr. McClure's team spent most of 2013 capturing and weighing birds to see how the traffic noise affected them. 

Dr. McClure expressed some compunctions about the stress his study created for the birds on his phantom highway.

"We basically ruined a great piece of habitat for two years," he told International Science Times. "But hopefully, that will lead to fixing a whole lot of other habitats."

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