At least 1,000 birds die from colliding with one Chicago building in a day

At least 1,000 birds died on Thursday (5 October) from colliding into one Chicago building. The birds migrated south to their wintering grounds.

Volunteers are still recovering bird carcasses within 1.5 miles of McCormick Place, the largest convention center in North America, which is largely covered with glass, reports The Guardian.

From late Wednesday (4 October) through early Thursday, a peak estimate of 1.5 million birds were in the air over Cook county, home to the Chicago metropolitan area. 

Carcasses of Tennessee warblers, hermit thrush, American woodcocks and other varieties of songbirds were recovered.

"Not every bird that hits the window is going to leave behind a body," Brendon Samuels told The Guardian. He researches bird-window collisions at the University of Western Ontario.

Samuels noted that the true extent of affected birds will unravel over a couple of days as people continue to pick up birds around downtown Chicago.

"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," he added.

Birds dying in large numbers in a small geographic area tend to occur during peak migration periods in spring and fall. Weather conditions like opposing wind, rain and fog can make it difficult for birds to orientate themselves, in addition to light pollution from cities that can draw them in and trap them among deadly structures.

"Anywhere you've got glass, you're gonna have birds hitting the windows," said Bryan Lenz at the American Bird Conservancy. 

Annually, up to a billion birds die due to collisions, and in the case of Chicago, the dead and injured birds were most likely flying from Canada en route to South and Central America.

Everywhere birds visit, they perform essential ecosystem services that have economic value and are necessary for the functioning of ecosystems. 

Following major wildfires like those in Canada, birds that return to burned areas can disperse seeds and aid forest landscape regeneration. 

Global increases in temperatures contribute to the increase in insect populations, and birds that feed on them can help curb the issues that pose a threat to humans and food systems.

Of all cities in the US, Chicago's light pollution poses the greatest risk for migrating birds. Turning off building lights is one way to reduce fatalities. 

A 2021 study done in McCormick Place, the same site of Thursday's bird deaths, found that shutting off half the lights in large buildings can reduce collisions by six to 11 times. 

McCormick Place is a participant of the Lights Out Chicago program, which has buildings voluntarily switch off or dim lights at night unless someone is inside.

"It is important to understand that there is an event going on at Lakeside Center [part of McCormick Place] this week, so, therefore, the lights have been on when occupied. Once the space is unoccupied, the lights have been turned off," said a representative from McCormick Place.

Having window glass with visual markers like dots or patterns can break up the appearance of reflection and let birds recognize whether there is a safe passage for them to fly through.

In 2020, Chicago approved a bird-friendly design ordinance but it is yet to take effect. In 2021, the Illinois governor, JB Pritzker, signed the Bird Safe Buildings Act, which "requires bird-friendly design to be incorporated into the construction and renovation of state-owned buildings" in the state, per Audobon.org.

"We have a lot of existing buildings that are killing birds, not just new construction," said Samuels, adding that investments in retrofits, creating tax credits for such environmental initiatives and making windows more bird-friendly can be an economical way to solve this. 

"We already have solutions, we just need to put those into policy."