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Chicago, Houston, and Dallas are the most dangerous cities for migratory birds in both spring and fall, according to new research published Cornell Lab of Ornithology scientists.

Researchers ranked metropolitan areas where, due to a combination of light pollution and geography, birds are at the highest risk of becoming attracted to and disoriented by lights and crashing into buildings.

The research combines satellite data showing light pollution levels with weather radar measuring bird migration density.

A stunned American Goldfinch after it crashed into an all-glass building in Connecticut

Top-10 Dangerous Cities for Migratory Birds

In spring, other metro areas on the top-10 list are Los Angeles, St. Louis, Minneapolis, Kansas City, New York, Atlanta, and San Antonio.

In fall, the most dangerous cities ranked fourth through tenth are Atlanta, New York, St. Louis, Minneapolis, Kansas City, Washington, D.C., and Philadelphia.

Because many birds alter their migration routes between spring and fall, rankings of the most-dangerous cities change slightly with the season.

Central U.S. Cities Biggest Threat During Spring Migration

Most During spring migration, billions of birds pass through the central U.S. between the Rockies and the Appalachians, so cities primarily in the middle of the country comprise the most-dangerous list for that season.

Massive 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, explaining why four eastern cities make the list in autumn.

“Chicago, Houston, and Dallas are uniquely positioned in the heart of North America’s most trafficked aerial corridors,” says study lead author Kyle Horton, a Rose Postdoctoral Fellow at the Cornell Lab.

This, in combination with being some of the largest cities in the U.S., make them a serious threat to the passage of migrants, regardless of the season.

American Redstart after building collision. Photo Credit: Ben Norman

READ: New Maps Forecast Bird Migration Using Radar

Bird Migration Traffic Key to Conservation Efforts

Although bird migration in spring and fall lasts for months, the most massive 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.

“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.

For example, Houston Audubon uses migration forecasts from the Lab’s BirdCast program to run ‘lights out’ warnings on nights when large migratory movements are expected over the city.

Migratory birds in light beams from the Tribute in Light in New York City, September 2017. Photo credit: Kyle Horton

Turn off the Lights

Horton notes that an estimated quarter-million birds die from collisions with houses and residences every year so 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,” says Horton.

“It’s a large-scale issue, but acting even at the very local level to reduce lighting can make a difference,” he adds.

While scientists are hopeful that significant reductions in light pollution at the city level are on the horizon, they’re excited that even small-scale actions can make a big difference.

Read the study published in Frontiers in Ecology and the Environment.