In an average year, about 1,000 to 2,000 migratory birds die from striking a lakeside Chicago convention center, reports Clare Marie Schneider for NPR.
But on one single night last week, at least 961 birds were killed after crashing into the building’s glass exterior.
“It was just like a carpet of dead birds at the windows there,” David Willard, a retired bird division collections manager at the Chicago Field Museum, tells Todd Richmond of the Associated Press.
“A normal night would be zero to 15 [dead] birds. It was just kind of a shocking outlier to what we’ve experienced,” he tells the news service. Museum volunteers have tracked bird deaths at the building for four decades, and they say no other single night has been so deadly.
With its mostly glass facade and location beside Lake Michigan, the building, called McCormick Place Lakeside Center, is a well-known bird hazard in the Windy City. Volunteers and researchers from the Field Museum visit the site daily during the spring and fall migration seasons to look for and collect bird carcasses, writes Amanda Holpuch for the New York Times. The center’s previous record was 200 bird fatalities in one night, per the publication.
Most birds migrate by night, relying on the stars for navigation—so artificial light emanating from buildings can be highly disorienting. The animals do not recognize windows as solid objects, and reflections on the glass can look like a continuation of the sky or the habitat that surrounds a building.
Chicago has been named one of the deadliest cities for birds because of its high light pollution and its placement along one of the continent’s most trafficked migratory flight paths, known as the Mississippi Flyway. Beyond the avian carcasses collected at McCormick Place last Wednesday, volunteers found an additional roughly 1,000 dead birds across the rest of the downtown area.
An update from our partner Willowbrook Wildlife Center on yesterday's collision victims. While 1,000 dead birds were being collected @McCormick_Place, our teams found hundreds of injured birds downtown. Read the full update from Willowbrook here: https://t.co/42PoflKuGF pic.twitter.com/lLsGM2p1Dj— Chicago Bird Collision Monitors (@BirdMonitors) October 6, 2023
But the city isn’t alone: Across the United States, between 365 million to about 1 billion birds die each year from colliding with glass in skyscrapers and low-rise buildings. Window strikes are the second-leading cause of bird deaths, behind cats. (Other human-caused threats, such as habitat loss, almost certainly kill more birds, but those are much harder to measure.)
At 3:40 a.m. on the morning of October 5, an unusually high number of birds—about 1.49 million—were in flight above Cook County, Illinois, where Chicago is located, according to BirdCast, an online tool that tracks bird migration. Poor weather conditions in the previous days—including heat and headwinds—had largely halted migration leading up to Wednesday.
“Birds like to fly in the fall when there is a north or a west wind, because they’re coming from areas north of us, and that gives them a literal and figurative tailwind to travel with,” Annette Prince, the director of Chicago Bird Collision Monitors, tells NPR.
On Wednesday night, however, temperatures dropped, and the wind shifted, leading a high number of birds to take flight on their journeys south. But early on Thursday, a storm system moved through the city and forced the birds to fly closer to the ground to avoid it, per the New York Times. By morning, carcasses ranging from Tennessee warblers to hermit thrushes to American woodcocks littered the ground outside the convention center.
In a statement posted on Instagram, McCormick Place acknowledged the bird fatalities.
“The well-being of migratory birds is of high importance to us, and we are truly saddened by this incident,” the post stated. “We deeply appreciate our community’s concern for the welfare of birds and your engagement with our efforts to mitigate these issues, and we are in discussion with industry experts to look for better solutions to protecting our avian neighbors.”
Per the statement, lights were turned on during an event last week, but they were turned off when the building was unoccupied.
Environmentalists and bird enthusiasts across the U.S. have long advocated for more bird-friendly architecture and reduced light pollution to help migrating birds reach their destinations safely. In 2021, Illinois passed a law requiring state-owned buildings to include bird-friendly designs in new constructions and renovations. Oakland, California; New York City; and San Francisco have also adopted regulations to help reduce bird strikes. Dozens of cities across the country participate in Lights Out programs to limit light pollution and protect birds.
“We’re hoping this incident, as tragic as it was, to be a wake-up call to any building in the city to turn its lights out during migration and to support the implementation of the bird-friendly guidelines for new development,” Prince tells Anumita Kaur of the Washington Post.