An estimated 600 million birds die from building collisions every year in the United States. Scientists at the Cornell Lab of Ornithology have published new research highlighting artificial light at night as a contributing factor.
The research was published in the journal Frontiers in Ecology and the Environment. It combines satellite data showing light pollution levels with weather radar measuring bird migration density.
Researchers ranked metropolitan areas where, due to a combination of light pollution and geography, birds are at the greatest risk of becoming attracted to and disoriented by lights and crashing into buildings.
Because many birds alter their migration routes between spring and fall, rankings of the most-dangerous cities change slightly with the season. During spring migration, billions of birds pass through the central United States between the Rockies and the Appalachians, so cities primarily in the middle of the country comprise the most-dangerous list for that season. Heavy spring migration along the West Coast also puts Los Angeles on the spring most-dangerous list. Fall bird migration tends to be intense along the heavily light-polluted Atlantic seaboard, which is why four eastern cities make the list in autumn.
In a statement to the press, lead author Kyle Horton, a Rose Postdoctoral Fellow at the Cornell Lab said: “Chicago, Houston, and Dallas are uniquely positioned in the heart of North America’s most trafficked aerial corridors. This, in combination with being some of the largest cities in the US, make them a serious threat to the passage of migrants, regardless of season.”
Although bird migration in spring and fall lasts for months, the heaviest migratory activity occurs during the span of just a few days. For example, a top-ranked light-polluting city can expect half of its bird-migration traffic to pass through over seven nights spaced out during the season; these nights are unique for each city and depend upon wind conditions, temperature, and timing.
Horton also notes that, given an estimated quarter-million birds die from collisions with houses and residences every year, even homeowners in these most dangerous metro areas for migrating birds can play an important role.
“If you don’t need lights on, turn them off,” states Horton. “It’s a large-scale issue, but acting even at the very local level to reduce lighting can make a difference. While we’re hopeful that major reductions in light pollution at the city level are on the horizon, we’re excited that even small-scale actions can make a big difference.”
Support for this study came from the Edward W. Rose Postdoctoral Fellowship, Marshall Aid Commemoration Commission, the Leon Levy Foundation, and the National Science Foundation.
Images, from above: An American Redstart killed in a building collision by Ben Norman, and Most Dangerous Cities For Birds Chart.