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SOURCE: The Guardian

DATE: April 7, 2019

SNIP: Scientists estimate that at least 100 million and maybe as many as a billion birds die each year in the US when they collide with buildings, especially glass-covered or illuminated skyscrapers. And, in a new report, conservationists now have a better idea which American cities are the deadliest for those on the wing.

Chicago, with its many glass superstructures that spike into what is the busiest US avian airspace during migration, is the most dangerous city for those feathered travelers. More than 5 million birds from at least 250 different species fly through the Windy City’s downtown every fall and spring.

They journey twice a year, many thousands of miles, going north in the spring from Central and South America, across the Great Lakes to Canada, and back south in the fall.

The famous skyline of Manhattan is another death trap for birds, especially those migrating.

“They wind up landing somewhere that’s unfamiliar, like a sidewalk somewhere,” said Susan Elbin, director of conservation and science at New York City Audubon, a leading bird advocacy organization. “Then when daylight comes, and they want to get more food, they’ll fly into a tree that they think is a tree, and it’s really a reflected tree in some glass building … Then they’ll slam into the glass, and then they die.”

Most birds migrating through the US do so at night, when the airspace is cool and calm – and often end up veering through cities because their glow stands out. Scientists have long known that birds are attracted to light, so when they fly over a bright city at night, they are naturally drawn toward it, unaware they are in dangerous territory.

Certain species of birds are more susceptible to building collisions. A separate study from the University of Michigan published this week found that songbirds, such as sparrows and warblers, are more likely to suffer collisions. Songbirds tend to emit “flight calls” during migration and are more likely to chirp when they see the bright lights of a city, potentially luring other birds into the treacherous skyline.