Some birds that strike windows may be killed outright, with fatalities almost always involving brain hemorrhage. Occasionally, groups of birds startled from feeding near large windows may all die, much to the dismay of the building's owner. Others rebound, flying away from the window with little if any apparent difficulty. But some birds fall to the ground, alive but unable to fly, at least for the moment. Among them, some are merely stunned and will recover without treatment, usually within an hour. However, other birds are more seriously impaired. The most common non-fatal consequence of a window collision is probably a shoulder injury.
Although the prominent joint at the top of a bird's wing may seem logically to be the shoulder, it is actually the wrist. In a wing held at rest, both the elbow and wrist joints are flexed, with the elbow closer to the feet and the wrist closer to the head. The avian shoulder girdle is too close to the center of the body to see or even palpate in a songbird. A bird with a fracture in one of the pectoral bones may hold its wings normally, and may even be able to fly short horizontal distances. However, the wing cannot be raised at the shoulder enough for the bird to achieve upward flight. Over time, the wing may develop a characteristic torque, as shown in these photos of a Mourning Dove recovering from a window strike.
When a bird is found alive on the ground after a window collision, it should be retrieved and removed from harm's way. If it is a raptor or songbird species capable of a strong bite (say, a cardinal or grosbeak), gloves can be worn, or the bird can be gathered up in a light towel. A good place for the bird to recover is a cardboard box lined with a rumpled towel or piece of clothing such as an old sweatshirt or t-shirt. Place the bird in the box, secure the lid (air holes may be punched first), put the box in a warm quiet place, and wait an hour. Then take the box outside and remove the lid. A bird that had merely been stunned will fly up and out of the box, but an injured individual will stay on the bottom of the box. Never force a bird to attempt flight by removing it from the box and tossing it into the air.
The recovery box should be too tall for the bird to leave by jumping. If a bird with an injured shoulder hops from the box, it may run or fly low to the ground quickly enough to elude recapture. However, a bird unable to achieve upward flight will be vulnerable to predation and starvation. If a cardboard box is unavailable, an alternative suitable for songbirds is a heavy paper grocery bag; again, a towel can be placed on the bottom, and the edges of the top stapled or taped together until it is time for a flight opportunity.
Shoulder fractures and other collision injuries can recover, but require skilled treatment. In some cases, recuperation may take several weeks. If the bird does not fly up and out of the recovery box, replace the lid, and contact a wildlife rehabilitator that is licensed for wild bird care.
Window collisions can be prevented! Decals such as those made by Window Alert can be affixed to windows; a large number of decals are needed for larger glass areas, however. Window cover products include CollidEscape™ and The Bird Screen. In visiting The Bird Screen website, several articles by Daniel Klem can be found by clicking on the menu for Windowkill Articles and Resources. Also available at that link is an article called "Window Pain," which was written for Birder's World magazine by David Sibley. In this article, Sibley describes several "do it yourself" strategies, including using fluorescent yellow highlighters to draw grids on windows (the grids are visible to birds, at least on sunny days, but not humans).