Researchers estimate that more than 600 million migratory birds die because of light pollution every year, mostly due to collisions with skyscrapers.

(Patricia Leonard/Cornell Lab of Ornithology)

At a Glance

More than 600 million migrating birds fly into skyscrapers and die every year.Researchers have named the top three deadliest cities for migrating birds.Light pollution attracts birds to cities and tall buildings.

The hundreds of skyscrapers in America’s largest cities are dangerous beacons for billions of migratory birds, either stopping them dead in their tracks or causing them to become so disoriented that they fly to the point of exhaustion, according to a from the Cornell Lab of Ornithology.

More than 600 million migratory birds die every year because of light pollution from skyscrapers, according to the report, either by crashing into the buildings or becoming confused by the light they emit. The study found that three of the nation’s largest urban centers were the most dangerous during both the spring and fall bird migration seasons.

"Chicago, Houston, and Dallas are uniquely positioned in the heart of North America’s aerial corridors,” study lead author Kyle Horton, a Rose Postdoctoral Fellow at the Cornell Lab, said in a release on the lab’s website. “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."

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Los Angeles, Atlanta, New York and St. Louis are among the other cities posing the biggest threats, the research found.

Light pollution is known to disturb wildlife in a multitude of ways, from change of habit and migration patterns to eating and sleeping and habits. Birds tend to crash into skyscrapers because they bright lights with stars they use to navigate by, or they might see a plant inside a window and think it is a good place to stop and rest.

There are more than 400 species of migratory birds in the U.S., and most of them travel at night. The Cornell lab researchers used weather radar images and other data from NOAA to track and map flight paths and light pollution between 1995 and 2017.

The study also showed that the top 125 urban areas in the U.S. account for just 2.1 percent of the country's land area, but emit 35.4 percent of the light radiance.

"Now that we know where and when the largest numbers of migratory birds pass heavily lit areas we can use this to help spur extra conservation efforts in these cities," adds study co-author Cecilia Nilsson, also a Rose Postdoctoral Fellow at the Cornell Lab.

Skyscrapers aren't the only danger: The reported also noted that about 250,000 birds die after crashing into houses and residences every year.

"If you don’t need lights on, turn them off," Horton said. "It's a large-scale issue, but acting even at the very local level to reduce lighting can make a difference."