By Ryan Baker

CHICAGO (CBS) — Chicago is known as the country’s deadliest city for migrating birds.

A newly released study using decades of research from the Field Museum is shedding some light on what needs to be done to cut down on bird collisions.

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“Well, in the case of these (birds), they would be window collisions from the Chicago region,” said Dave Willard, a bird scientist with the Field Museum.

“One of the reasons is that it is heavily lit at night. The other is its situation on Lake Michigan,” Willard said.

He added that he’s held thousands of dead birds who were victims of Chicago’s skyscrapers.

“Just from the Chicago region, I’ve probably handled and measured 100,000 dead birds,” Willard said.

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Most of those birds were killed after crashing into McCormick Place. Willard has tracked and tagged birds for more than 40 years.

His decades of work helped researchers determine that turning off half of the lights would cut collisions by 11 times in the spring and six times less in the fall.

“The goal is to get as many lights off as we can. Certainly on any building with exposed glass windows. It’s very important,” Willard said.

The city currently has a “lights out” program which requires high rises to shut off external lights during peak migration season.

The new study is focusing on the importance of dimming inside lights as well.

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In the past year when it was mostly dark during the pandemic, McCormick Place had its lowest number ever of deadly bird collisions.