Chicago buildings in the Lights Out program report up to 80% fewer bird collision deaths — achieved by dimming upper floors from 11 p.m. to sunrise during spring and fall migration.
Chicago sits inside one of North America’s major migratory corridors, and its illuminated skyline acts as a fatal trap for nocturnal birds passing through each spring and fall. Artificial light pulls migrants toward tall buildings the same way a flame attracts moths — not by design, but by physics. Birds navigating by stars suddenly find a brighter signal competing with the sky.
Building collisions erase roughly 1 billion birds per year across the United States. That toll isn’t driven by predators or storms. It comes from glass.
How Chicago’s Lights Out Program Actually Works
The Chicago Lights Out program is a voluntary initiative, not a city ordinance. It is managed by the Chicago Audubon Society in partnership with the Building Owners and Managers Association, the National Audubon Society, and the City of Chicago.
The ask is straightforward: building owners reduce exterior and interior lighting from 11 p.m. until sunrise during the two peak migration windows. Spring timing runs March 15 to June 15. Fall timing runs August 15 to November 15.
The program targets buildings of 40 or more stories, or 20-plus stories if isolated from other tall structures. No new technology is required. No construction. Dimming decorative lights and minimizing lobby brightness is enough.
Why Artificial Light Pulls Nocturnal Birds Off Course
Nocturnal migrants navigate using stars and moonlight — signals that evolved over millions of years. Urban glow introduces a brighter, competing source that draws birds toward city centers.
Once inside that light envelope, birds circle in exhaustion. They lose altitude. They hit glass they never registered as a solid surface.
Reducing visible light from upper stories and glass façades breaks that trap. The birds that were being drawn in simply aren’t pulled toward the building in the first place.
What the 80% Collision Reduction Figure Actually Means
Participating Chicago buildings report up to 80% fewer bird collision deaths during active program periods. That figure comes from program materials and is presented as a program claim rather than a universally verified, independently audited citywide outcome.
It is still a striking number. And it arrives without replacing a single pane of glass.
That 1-billion-bird annual toll has no single fix. But in Chicago, a voluntary dimmer switch — applied seasonally, at the right hours — demonstrates what a localized mechanism can actually accomplish.
One corridor, two seasons, and a commitment to darkness after 11 p.m. That is the whole intervention.
Frequently Asked Questions
How many birds die from building collisions in the U.S. each year?
Building collisions kill roughly 1 billion birds per year in the United States, according to conservation and research sources cited by the Chicago program.
Is Chicago’s Lights Out program a law?
No. It is a voluntary program managed by the Chicago Audubon Society and partners, asking building owners to reduce lighting during migration seasons — not a city ordinance requiring compliance.
What hours and dates does Chicago’s Lights Out program cover?
Participating buildings reduce lighting from 11 p.m. until sunrise. Spring migration runs March 15 to June 15; fall migration runs August 15 to November 15.
Which buildings does the Chicago program prioritize?
Buildings of 40 or more stories, and buildings of 20 or more stories if isolated from nearby tall structures, are the primary focus.