Window Kills

Window Collisions

Bright Lights, Big Cities: Lights & Windows are Deadly Hazards for Birds


At least 100,000,000 birds are killed and even more are injured every year across North America by collisions with windows. Ornithologists have been studying this phenomenon for decades and their findings are very conclusive: birds simply do not recognize glass as a barrier. During daytime, birds often fly head-on into windows, confused by the reflection of trees or sky. This is a common occurrence even in the suburbs at homes and glassy office campuses. Of the birds that suffer head trauma, over half die.

Additionally, scientists have observed that at night the bright lights of buildings seem to confuse birds, especially during cloudy, foggy or rainy weather. Large masses of birds have been photographed during the night at one of Chicago's skyscrapers, the birds continually circling and battering the building lights. By dawn the birds are either dead or seriously injured. These birds were migrants on their twice-yearly, night-time migration. During some weather conditions and at certain "killer" buildings, the death toll can be in the hundreds per day.

Birds are attracted to the lights not only at the tops of the buildings but also to the lights in mid-level office windows and ground level lobbies and atriums. Recent research by ornithologists at the Field Museum of Natural History confirmed that simply turning off bright lights or closing blinds reduces bird deaths by 83%.


You can make a difference

Because of the enormity of the situation (after all, lights and windows are everywhere) many people find the problem too daunting to tackle. Don't be discouraged: there are many easy actions you can take at your home and office to significantly reduce the number of birds killed.

Even not washing the windows during the migration months helps keep the reflective qualities low and, thus, can help reduce bird injury and death.


Click here for tips from BCN on how to better protect birds from building collisions at your home or office.

And, please talk to the owners, managers and maintenance staff of your office building about what can be done to make the facility bird-friendly. Give them a copy of the BCN Window Collision Fact Sheet (.pdf format - 102KB) and make them aware of the meaningful contributions they can make to save the lives of hundreds or thousands of birds each migration season.


Download the free Adobe® Reader® to view .pdf files: "Get Adobe Reader"


Additional Information

More tips and information about birds and window collisions can be found on the

Blackburnian Warbler
Chicago Bird Collision Monitors website.  CBCM is an organization that works in the Chicago area to rescue migratory birds injured from striking buildings, and to mitigate the risk of bird-building collisions by educating the public & working with building managers to find solutions.


Lights Out is a voluntary partnership between the Chicago Audubon Society, the Building Owners and Managers Association of Chicago, and the Chicago Department of the Environment, working to see that virtually all Chicago’s tall buildings extinguish their lights during the migration season.  The Lights Out website has information about the Chicago program and a “Tool Kit” that other cities can use to emulate our success.

Working Together for Birds and Habitats

In The Spotlight

Chicago Bird Collision Monitors

"The Chicago Bird Collision Monitors put in hours patrolling the early morning streets of Chicago, collecting and rescuing birds that have struck windows in the one-square mile area that constitutes the Loop. It is both a triumphal and sobering vigil, kept by people who rise at 3:00 in the morning to take an early morning train to arrive before sunrise."

Chicago Urban Nature Examiner