Study highlights America’s most dangerous cities for migratory birds

cities
This Yellow-rumped Warbler died in 2014 after striking a building in the Washington, D.C., area. Photo by Sam Droege/U.S. Geological Survey (Public domain)

Chicago, Houston, and Dallas are the most dangerous cities for migratory birds in the lower 48 states in both spring and fall, according to new research published today by Cornell Lab of Ornithology scientists.

They’ve 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. 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.

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. During spring migration, billions of birds pass through the central U.S., 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. 

“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,” notes study lead author Kyle Horton, a Rose Postdoctoral Fellow at the Cornell Lab.

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.

“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.”

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.”

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