Unfortunately about half of the birds that collide with windows die, either from injuries caused by the collision itself or by another animal when the bird is stunned and unable to fly away.
Ornithologists believe that the birds, which are usually small songbirds, are probably seeing the reflection of trees and open sky in the window, and think that they have a clear flight path. Your local ornithological society can give you tips on how to make your windows bird-safe and what to do if you find a stunned bird that has flown into a window.
