Most songbirds migrate at night and rely, in part, on the stars to navigate. Light pollution from urban areas can throw birds off course, drawing them into a maze of tall structures and glass where they often collide with buildings. Especially on foggy or rainy nights when the cloud cover is low, birds fly at lower altitudes and are more likely to be disoriented by city lights.
Certain point sources of light can also be incredibly dangerous for night-migrating birds. These include floodlights, lighthouses, communications towers, cruise liners, gas flares, oil platforms, and airport ceilometers. Birds become attracted to these sources of light and may become trapped inside the light beams, flying around until they drop from exhaustion.
During the day, migrating songbirds need to find places to rest and refuel. Urban parks, woodlots, and even landscaped vegetation and green roofs can be attractive rest stops. During these rest breaks in urban areas, birds may come face to face with glass on buildings or other structures and risk a fatal collision.
Birds can see through glass and what is reflected on glass (such as trees or sky), but they cannot see the glass itself. Because birds can’t perceive glass as a solid object, they often collide at full speed—the result is often fatal.
It is important to note that all architectural uses of glass can be dangerous to birds. This includes but is not limited to structures such as glass railings, glass linkways, bus shelters, wind breakers, and sound barriers. Other building materials such as polished steel and marble can also be highly reflective and hazardous.
Photo: FLAP Canada
Collisions with glass are one of the top ways that humans are killing birds. Recent estimates suggest that in Canada alone 16-42 million birds die each year by colliding with glass. Estimates in the United States suggest that close to one billion birds may be killed annually by window collisions.
