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Glass and Daytime Collisions

The growth of dense, urban areas along ancient, bird migration routes poses a significant and often fatal threat to migrating birds. Ornithologists now claim that bird collisions with human-built structures is a leading cause of bird death across North America.

Photo: Sara Scharf/FLAP

birds cannot see glass. They see a reflection of their habitat (trees, bushes, water, sky) in windows or in the mirrored exteriors on office towers and other structures, but they cannot see the glass. From a bird’s perspective, glass is an invisible barrier to their habitat.

Deceived by the reflection, and unable to detect the presence of glass or mirrored exteriors as solid objects, birds often collide head-on with the windows and buildings themselves. Many migratory birds die on impact, or sustain serious injuries that prevent them from continuing their journey. Stunned birds fall to the ground and become vulnerable to predation.

Migratory birds will also collide with the clear glass on structures like greenhouses, solariums, bus shelters, linkways between buildings, or with windows that meet at the corners on homes or workplaces. They see through these glass structures to the trees or bushes on the other side, and strike the glass in an attempt to find refuge. The same will occur when they see interior, ornamental trees and plants in glass-walled lobbies or through the windows on our homes.

Daytime collisions often occur when migrating birds become trapped in the city after colliding with a building during the night. The lights of our cities can often disorient migrating birds at night and draw them off course.

Nashville Warbler
(Photo: Sara Scharf/FLAP)

Any birds that survive a night-time collision can find themselves lost in a maze of reflective windows and shiny exteriors during the day. The birds collide with buildings in an attempt to seek a safe retreat from humans.

FLAP and the City of Toronto have collaborated on several innovative programs with a goal to saving the lives of migratory birds as they travel through our city.

Learn more about Lights Out Toronto! (LOT!) and the City of Toronto’s Bird-Friendly Development Guidelines. The strategies presented in the guidelines and in LOT! help reduce habitat reflection during the day, and unnecessary lighting at night, and are completely adoptable for use in any city.

Click here to learn how you can make your home and workplace safer for migratory birds.

Do you have any or comments or questions? Please email us at, or call us at (416) 366-3527.