Chicago skyline
Chicago skyline. Image Credit: Pixabay

Nearly 1,000 birds struck a building in Chicago and dropped dead during their migration route last week - a stunning number of bird deaths against a single building in one day, advocates say.

On Thursday morning, the bodies of warblers, woodcocks and sapsuckers - among other species - littered the ground around the glass-covered McCormick Place, the largest convention centre in North America. Volunteers have continued recovering the carcasses of birds that crashed into McCormick Place and other glass buildings in Chicago.

The loss is immense, given that birds are critical to the global ecosystem, said Annette Prince, director of Chicago Bird Collision Monitors, a volunteer group dedicated to the protection of migratory birds.

“When we say we found a thousand birds, that’s just a snapshot - beyond the one square mile we look at, there could be so many more,” Prince said.

Wednesday night into Thursday morning brought the “perfect storm” for bird strikes, according to Prince. Thousands were migrating through the Chicago area, combating a brisk wind, cloudy skies and the glassy exterior of McCormick Place - which sits along Chicago’s lakefront area, an ideal resting place for birds. That night, the building’s lights were left on for an event, even though bright lights at night are known to disorient birds.

The birds’ bodies have been turned over to Chicago’s Field Museum for study, Prince said.

The building’s management acknowledged in a statement Friday that an event kept the centre’s lights on last week but said that it otherwise participates in a citywide “lights out” programme, which aims to reduce the number of bird collisions in Chicago by having buildings turn off or dim lights when not in use.

“McCormick Place learned that on Wednesday night an extremely large number of migratory birds died after colliding into the Lakeside Centre and other campus buildings. This was due to unusual weather during the peak of the Fall 2023 migration season in the city coupled with avian confusion that comes from light emanating from buildings,” the building’s statement said. “The well-being of migratory birds is of high importance to us, and we are truly saddened by this incident.”

Up to a billion birds die annually in the United States in building strikes, according to the American Bird Conservancy. And Chicago has been named one of the deadliest cities in the country for migrating birds because of its location on their routes, its glass architecture and its level of light pollution. In 2020, the Chicago City Council passed an ordinance requiring all new buildings to be designed with bird-safe features, and in 2021, Illinois Gov. J.B. Pritzker (D) signed the Bird-safe Buildings Act, which required bird-friendly construction and renovation of state-owned buildings.

But the bird-friendly policies have yet to be implemented in full, Prince said.

“In Chicago, we see amazing numbers and varieties of birds that are not residents here but are simply passing through as visitors here. We’re hosting them as little tourists, and we owe them safer passages,” she said.

Mitigation can include adding nets that act as barriers in front of windows or applying special films to glass windows to ensure birds can figure out where to fly. Those measures are especially important for buildings that exist along green spaces that birds enjoy, such as the lakefront area by McCormick Place, Prince said.

“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,” she said.