On 5th October 2023, more than 1,000 birds died from colliding into McCormick Place in Chicago, US, the largest convention centre building in North America. Tennessee warblers, hermit thrush, American woodcocks and other songbirds were migrating from Canada south to their wintering grounds, but they did not see the building due to its glass surface and confusing reflections. From the day before, an estimated 1.5 million birds were flying over the Chicago metropolitan area. Annually, up to a billion birds die due to collisions with buildings.
Annette Prince, director of Chicago Bird Collision Monitors, said to the Guardian, “It’s the tip of an iceberg but it’s a huge, huge amount of birds we found both dead and injured.” Brendon Samuels, researcher from the University of Western Ontario who studies bird-window collisions, said, “Not every bird that hits the window is going to leave behind a body. In fact, we often see birds collide with glass and they continue flying some distance away, seriously injured in ways that ultimately they won’t survive past a few hours.” Bryan Lenz, from the American Bird Conservancy, said, “Anywhere you’ve got glass, you’re going to have birds hitting the windows.”
Chicago’s light pollution and very numerous and big glass buildings poses the greatest risk for migrating birds from Canada, but some things can be done to reduce it. A 2021 study from McCormick Place found that shutting off half the lights in large buildings can reduce collisions by six to 11 times. The Lights Out Chicago program has buildings voluntarily switch off or dim lights at night unless someone is inside. Having window glass with visual markers like dots or patterns can also prevent reflection and let birds identify there is an object on their path.