964 Birds Fatally Strike Chicago Building in One Night

On a typical morning, as many as 15 birds might be found dead outside Chicago's McCormick Place Lakeside Center, having fatally struck the building the night prior. On Thursday morning, a nearly unimaginable 964 of them were found dead, and another 80 were found stunned but still alive, according to the National Audubon Society. "It was just kind of a shocking outlier to what we've experienced," a retired bird division collections manager at the Chicago Field Museum tells the AP. "In 40 years of keeping track of what's happening at McCormick, we've never seen anything remotely on that scale." As other experts from the Field Museum, a natural history museum that checks the convention center each morning during spring and fall bird migration seasons, explain to the New York Times, a number of factors played a role in Thursday's sad scene:

• More birds than usual were migrating Wednesday night: That's because unfavorable weather, which had kept birds from traveling through the area earlier, cleared up that night—leading to what the Times calls "a huge number of birds" to take wing. Around 1.49 million were tracked in flight above Cook County at 3:40am Thursday.
• Weather played a role: While the unfavorable weather (unusually high temperatures and a headwind) had cleared up Wednesday night, a small storm system then moved through the area in the wee hours of Thursday. "The birds hit this storm and they drop out, they don't want to fly through the storm," a Field Museum senior conservation ecologist says. "So they come down to the ground, and that sets up the conditions for the incredible migration we saw—and for the big kill we saw" when the birds encountered a mostly-glass structure with its lights on.
• The building also played a role: While the convention center overlooking Lake Michigan is not that tall compared to the skyscrapers in the vicinity, its exterior is made mostly of glass. As the experts and the AP explain, birds can't see clear or reflective glass and don't understand they can't fly through it, and birds that migrate at night are confused by lights, since they use the stars to navigate. McCormick Place said in a statement it has made efforts to reduce bird strikes by dimming or turning off decorative lights, which the Chicago Audubon Society encourages building owners to do, but notes that the lights had sometimes been turned on during the week of the bird strikes due to an event. (The AP says the lights were on when the birds hit.)
• Impact: "It was just like a carpet of dead birds at the windows there," the retired collections manager says of the songbirds, which represented 33 different species, that died. "You pick up a Rose-breasted Grosbeak and realize, if it hadn't been for a building in Chicago, it would be spending its winter in the foothills of the Andes." The dead birds will be placed in a flesh-eating beetle colony, and then their skeletal remains will be used for research or added to the Field Museum's collection.

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