Reducing Bird Collisions with Windows provides information about how to reduce bird collisions with windows. In the US alone, millions of birds die each year from colliding with windows. The guide includes several suggestions for simple solutions we all can do to help turn this problem around.
Some birds simply become stunned as a result of a window collision. If you suspect that a bird has become stunned from hitting the window or wall, put it in a shoebox with holes and a soft towel. Then, carefully open the box and see if the bird can safely fly away.
If the bird is more seriously injured, contact your local wildlife rehabber.