Advocates and volunteers say over 1,000 birds were killed or injured after colliding with buildings in the Chicago area during fall migration this past weekend.
Most birds were rescued or recovered in and around downtown Chicago and on Northwestern University’s Evanston campus Saturday and Sunday, according to collision monitors.
Advocates say the devastating toll highlights the urgent need for “effective, preventive measures,” specifically a Bird-Friendly Building Design Ordinance to establish protections for qualifying new buildings in Chicago. Besides policy-level action, they say design choices and reduction of light pollution in existing buildings can address preventable collisions.
Chicago, which sits along a major migratory route — the Mississippi Flyway — is the most dangerous U.S. city for millions of birds migrating in the spring and fall, according to Cornell University’s renowned Lab of Ornithology. According to the lab’s BirdCast, over 5 million birds crossed Cook County on Friday night.
Experts estimate that a billion birds die crashing into windows in the United States every year. For context, BirdCast estimates that about a billion birds were in flight over the contiguous states Friday night.
Another such night in the country also led to a similarly deadly mass collision in Chicago three years ago when, in early October 2023, 960 birds died at McCormick Place Lakeside Center. Experts say the event marked the most bird collision deaths ever recorded in the country in a single day.
Glass buildings are particularly deadly to birds, advocates say, as the reflections of trees and the sky — or transparent glass that is essentially invisible — can trick them into thinking it’s safe. Birds often strike glass flying as fast as 30 mph, suffering fatal brain trauma or devastating injuries. In cities, they can also become disoriented at night by artificial lights.
In March, Ald. Maria Hadden, 49th, introduced an ordinance to amend the city’s building code and require bird-friendly design on non-residential and high-rise buildings. It was sponsored by Brian Hopkins, 2nd, and Ruth Cruz, 30th, and co-sponsored by 18 other City Council members.
After leaving the rules committee in the summer, the proposed ordinance is now sitting in the zoning committee led by Ald. Gilbert Villegas, 36th, where it is undergoing some revisions in language before being called up for a vote.
Opponents of the ordinance have claimed it would stall development and increase the cost of construction. But proponents say including bird-friendly glass from the beginning can increase a large development’s total budget by less than 1%.
Some design measures to prevent bird collisions include patterned glass, exterior screens or other visible treatments that can help birds recognize windows as a barrier.
The windows at McCormick Place Lakeside Center encompass an area of 120,000 square feet. After the 2023 carnage, the Metropolitan Pier and Exposition Authority (which owns and operates the center) applied visible markers — a film of tiny dots — to the glass, reducing bird collisions by 95%
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, according to an analysis by the Field Museum.For decades, the convention building caused about 1,000 deadly collisions per year. Since the film was applied, the deaths reportedly plummeted to 18 in the fall of 2024.
Beginning in October 2023, the convention center also reportedly implemented additional new bird-safe measures, including closing drapes and blinds overnight and turning off non-essential exterior lights.
The city of Chicago, alongside the Chicago Bird Alliance, the Chicago Bird Collision Monitors and the Building Owners and Managers Association, has since 1995 encouraged buildings — either tall or located alongside the Chicago River and Lake Michigan — to participate in the Lights Out Chicago program and turn off or dim decorative and non-essential lighting every night in the spring and fall, from 11 p.m. until sunrise.