We take glass for granted — most of the time– so it can be surprising to us that birds would run into windows. But birds don’t see glass, and neither do we. But people have learned to adapt to a world of glass-enclosed spaces. Most birds haven’t experienced glass in their own habitats, so they don’t recognize it when they encounter during migration.
Birds hit buildings for three main reasons:
- see-through buildings
- artificial lights
During the day, birds can fly head-on into windows, confused by the reflection of trees, clouds, buildings, or skyline in building facades.
We can be confused by reflections too, but we read other cues, such as window frames, to help us distinguish reflection from reality.
Birds also collide with glass when they attempt to fly towards something, like the tree in the lobby pictured below, that is visible– but inaccessible– because of a glass barrier.
It’s become popular to plant trees in large glass atria. But these lobbies are a real hazard to migrating birds searching for food and shelter when they stopover in cities.
At night, artificial lighting can confuse migrating birds, causing them to fly until they are exhausted.
Some birds use the stars to navigate their routes. Light pollution from cities interferes with their ability to navigate.