More than a thousand migratory birds died after colliding with a Chicago convention facility in the United States. The tragedy underscores the danger that certain manmade structures pose to wildlife when built without regard for the surrounding ecosystem and biodiversity.
Following the incident, Field Museum staff in Chicago collected well over a thousand birds that had struck the McCormick Place Lakeside Center during their flight near Lake Michigan. The center sits along the lakefront, a route commonly used by birds migrating south for the winter. According to Chicago Bird Collision Monitors director Annette Prince, the scale of the harm was immediately evident.
Volunteers with the nonprofit organization later retrieved an additional thousand birds in downtown Chicago. While some individuals survived the impact, researchers and volunteers noted that many appeared injured and would likely succumb to their wounds in the hours or days after the collision.
Among the carcasses recovered near the building were Tennessee warblers, hermit thrushes, and sandpipers, reflecting the mix of species that use this migratory corridor. Specimens of various species were photographed and cataloged for study after removal from the site.
Specimens laid out after collection reminded observers of the scale of loss, described by Prince as overwhelming and tragic. She recalled arriving at the building and finding a scene that looked like a carpet of birds in distress, both dead and dying, across a broad area.
Early October coincided with a peak in migration, when many birds prepared to move south for the winter. The prevailing winds that night were shifting in ways that would help carry flocks along their migratory routes, with some birds awaiting favorable conditions before taking to the air.
When a favorable wind arrived, many birds launched into flight in rapid succession. Fog and low clouds on that evening obscured the outlines of buildings, potentially increasing the risk of collisions. McCormick Place, located near the lake, is frequently one of the first major structures encountered by birds crossing Lake Michigan during migration.
The collision was caused by light pollution
Light pollution played a significant role in the incident, as illuminated structures can lure nocturnally migrating birds to navigate toward bright facades and reflective surfaces. These lights act much like beacons for birds at night. Prince noted that the lights were a strong attraction for birds, almost like a lighthouse guiding them toward danger.
Even during daylight, birds continued to collide with the McCormick Place Lakeside Center. The persistence of harm is attributed to the way large, transparent glass panels can confuse birds, who perceive the glass as open sky and fail to recognize it as a barrier. The outcome is often fatal when a bird cannot maneuver away in time.
A 2019 report from researchers at the Cornell Laboratory of Ornithology estimated that in the United States alone, roughly 600 million birds die each year from building collisions. During peak migration seasons in fall and spring, Chicago has been identified as one of the most dangerous cities for birds, with other studies suggesting higher figures of one billion dead birds annually in the United States. These numbers reflect a broad pattern that many species face when urban development intersects with migratory pathways.
Observing the situation, environmental advocates emphasized that while the public appreciates the aesthetic appeal of clear or reflective glass, there is a need for a change in approach. The goal is to reduce wildlife fatalities without compromising the architectural or functional value of modern structures. As Prince stated in a note shared with media, the visual beauty cannot justify the loss of hundreds of thousands of animals at risk during migration seasons.
The episode serves as a stark reminder of how human-built environments intersect with natural processes. It highlights the ongoing responsibility of cities and building owners to adopt bird-friendly designs and lighting strategies that safeguard migratory species while supporting urban life. Researchers and conservationists continue to study the incident to develop practical measures that can prevent similar tragedies in the future, such as reduced nighttime lighting during peak migration periods, bird-safe glass technologies, and improved urban planning that considers wildlife movement patterns. These efforts aim to balance human needs with ecological preservation, ensuring that skylines do not come at the expense of birds in flight.
For more information on the impact of glass and lighting on migratory birds, ongoing studies from ornithology and conservation organizations offer guidance and actionable steps that communities can implement to protect wildlife during migration seasons. (CITATION: Cornell Lab of Ornithology; Chicago Bird Collision Monitors; American Bird Conservancy)
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