This article is from the Birds FAQ, by Lanny Chambers with numerous contributions by others.
Most people's encounters with injured wild birds happen around plate-glass
windows. Birds strike glass windows and doors frequently, apparently
because of the reflections of sky they create. In most cases, the bird
is simply stunned. The best way to save the bird's life is to shoo
potential predators from it until it recovers and flies off.
Some people contend that taping hawk silhouettes to windows makes bird
strikes less frequent. Others contend that this technique has little
effect, and still others suggest that any window marking works as well.
Putting up hawk silhouettes does have the positive effect of making
passing humans think about birds.
If you find a large bird, such as an owl, a hawk, or a vulture, that
has been wounded, you may wish to contact a rehabilitation center, such
as the Carolina Raptor Center (704-875-6521) or the Vermont Raptor
Center (802-457-2779), for assistance. Some rehabilitation centers
also accept non-raptor birds or other wildlife, such as WildCare
(415-456-7283, http://www.wildcaremarin.org), or the Ontario
Veterinary College's Wild Bird Clinic (519-824-4120, ext. 4162).
For more information about rehabilitation, including directories by state,
province, and country, see:
Be aware that touching large wild birds can be dangerous.