Millions of migrating birds are moving through the Chicago area as they head south for the winter, bringing one of the busiest periods of the fall migration season over the city.
An estimated 296 million birds were expected to pass over the Chicago region Wednesday night, with another 276 million forecast to make the journey Thursday night.
The large migration is part of an annual trip that takes many birds from breeding grounds in Canada and the northern United States toward warmer areas farther south. Some will continue as far as Florida and South America.
Cooler, drier weather can help trigger stronger migration nights. Many birds travel after dark, when conditions are generally calmer and they can use natural cues such as the stars and moon to navigate.
Weather radar can sometimes detect heavy migration as a pattern that resembles precipitation. When migration is especially strong on a clear night, thousands or even millions of birds moving through the atmosphere can appear as radar clutter.
Chicago’s skyline creates a dangerous obstacle
The city’s location along a major migration route puts birds directly in the path of dense development.
Chicago’s buildings can become particularly hazardous at night because artificial light can interfere with birds’ normal navigation. Glass creates another danger because birds may not recognize windows as solid surfaces, or may see reflections of trees and sky and attempt to fly toward them.
More than 250 bird species pass through the Chicago area during migration seasons, with millions of individual birds making the journey.
Bird collisions are not limited to the tallest buildings. Glass facades, illuminated atriums and windows near vegetation can all create risks for birds moving through urban areas. Research and local monitoring have also shown that reducing nighttime lighting can substantially lower bird deaths at problem buildings.
A simple step can make a difference
Residents and building managers can help by turning off unnecessary lights during periods of heavy migration.
Chicago’s Lights Out program recommends reducing or shutting off nonessential lighting after 11 p.m. and keeping it off until daylight during the fall migration period, which runs from Aug. 15 through Nov. 15. People living or working in upper floors can also close blinds or curtains at night.
For homes and smaller buildings, closing blinds and shades can reduce the amount of indoor light visible from outside. Avoiding unnecessary exterior lighting can also make windows less attractive to birds flying through the area.
Indoor plants placed directly beside windows can create an additional hazard because birds may mistake the vegetation for a safe place to fly. Moving plants away from windows and keeping shades closed at night can reduce that risk.
Chicago continues efforts to reduce bird collisions
The push to make Chicago safer for migrating birds has gained additional attention as officials and bird advocates consider stronger protections for buildings.
A proposed Chicago City Council ordinance would establish bird-friendly requirements for certain new construction and major renovations. Supporters argue that voluntary efforts have helped but that additional building standards could further reduce collisions.
There is evidence that changes to individual buildings can have a major effect. After a 2024 retrofit at McCormick Place, bird strikes at the convention center were reported to have fallen by 95 percent.
For now, the most immediate help can come from reducing unnecessary light during heavy migration nights.
As thousands of birds continue crossing Chicago after sunset, a darker skyline and covered windows can give them a safer route through the city.
