Hamburg, Pa. — While it doesn’t affect many huntable species, the glow of artificial light in cities at night is bringing unforeseen devastation to migrating birds, according to the Cornell Lab of Ornithology.
A new study by lab researchers has found that those bright city lights are drawing passing birds into zones of high concentrations of airborne toxic chemicals common to urban environments.
“Light pollution does indeed increase exposure to toxic chemicals when birds stop to rest during spring and fall migration,” noted Frank La Sorte, lead author of the lab’s study of 165 nocturnally migrating songbird species.
To determine the birds’ exposure, the researchers first compared levels of artificial light at night with the presence of 479 toxic chemicals from 15,743 sources across the U.S. They found that higher light pollution did correlate with higher levels of airborne toxic chemicals.
The scientists then cross-referenced the data with the weekly abundance of 165 night-migrating songbird species throughout their annual life cycles, using data from the Cornell Lab’s eBird program, an online reporting system for birders.
Previous studies demonstrated that air pollution caused some species to stop migrating, change migration altitude or alter their course.
Long-term exposure to toxic chemicals can interfere with cell and organ function. Contamination can carry over to young birds through the transfer of chemicals from a nesting female to her eggs.
“Efforts to reduce light pollution during the spring and autumn would reduce the chances of toxic chemical contamination during migration stopovers, which would improve survival and reproductive success,” La Sorte said.
“However, this would have no effect on the long-term exposure occurring along the U.S. Gulf Coast, a region that could be a significant source of toxic chemical contamination for North American birds,” including many species that spend the spring through fall in and north of Pennsylvania.
The researchers also found that the birds’ exposure to toxic chemicals is high during the non-breeding season, which is a time when the birds typically avoid city lights.
The only time that did not reveal increased exposure to toxic chemicals was
during the breeding season, a period when songbirds typically nest in
habitats away from areas of intense human activity.
Several Pennsylvania cities have ongoing efforts to encourage lights-out
periods in their tall buildings during periods of migration.
While those efforts were launched to reduce bird collisions with windows on
lighted buildings, the new study by the Lab provides additional reason
to continue the programs.