Chicago: at least 1.000 birds fly against tall building and die

The Guardian reported on Thursday, October 5, that at least 1,000 birds had collided with a Chicago conference center during their southbound migration (at least 1,000 birds died from colliding with one Chicago building in one day | Chicago | The Guardian). The building’s exterior is largely made of glass, Volunteers were still collecting dead birds from a 1.5-mile radius around the building. A complete tally of the total number of birds killed by the collision will only be available after a few days. Birds that collide with a window often fly farther but still die after a few hours from serious injuries they sustained.

During birds migration in spring and autumn, spikes in mortality are often observed due to birds flying into buildings (this is a well-known problem in the Netherlands, for example, with the woodcock: The Woodcock remains a bad pilot | Sovon). But the number of birds that have crashed into a single building in Chicago in a single day is exceptional. Adverse weather (headwinds, rain, and fog) during bird migration, combined with light pollution in cities, can attract birds to the city, where they then crash into buildings to their death.

It’s common knowledge that birds collide with windows to their death. Bryan Lenz of the American Bird Conservation Society indicated that a billion birds die each year from hitting a window. In Chicago, these are likely birds flying from Canada to South and Central America.

Keeping lights off in buildings during the evening and at night is one way to reduce the number of birds fatalities. A 2021 study showed that in McCornick Place (the same area where the birds died in this report), turning off half the lights in large buildings reduced the number of bird collisions by a factor of 6 to 11.

A new Illinois law on bird-friendly design is expected to reduce the number of birds that collide with buildings to their death (New Law Will Protect Illinois Birds From Deadly Building Collisions | Audubon Great Lakes).