Building collisions are a leading cause of bird fatality during migration in North America, with the American Bird Conservancy estimating that up to one billion birds die each year in the United States from building collisions.
Why do window strikes happen?
- Birds cannot see glass, they can only see what the glass reflects.
- Glass often reflects open sky, trees, and other vegetation that is desirable to the birds. Collisions occur when birds attempt to access this reflected habitat and fly into the glass.
Why is nighttime lighting a problem?
- Birds are attracted to artificial lights at night, drawing them into light-polluted city centers and increasing their chances of striking a building
- This problem is amplified during spring and fall migration, as most of our native birds migrate at night
- Nocturnal migrators use the moon and stars to aid in navigation and become disoriented by artificial lights at night; birds may confuse building lights for stars and fly in circles around the buildings and die of exhaustion or collide with the windows
What factors make buildings unsafe for birds?
- Windows: More glass leads to more strikes. As the percentage of window surface on a building increases, so does the risk of avian mortality
- Height: Buildings do not have to be tall to be a threat to birds; most collisions occur in the first 3 floors of a building. While tall buildings kill more birds per building, individual residences kill more birds cumulatively
- Vegetation: Landscaping near building windows attracts birds
- Trees reflected in windows and potted plants inside windows confuse birds and increase the chance of a collision