We often hear about birds lost to window strikes. Skyscrapers have been the subject of many news articles on the numbers of birds who hit reflective windows during migration. Some architects and builders have worked on window designs and glass materials to avoid bird strikes. Swarthmore College, near my boyhood home in Pennsylvania, designed a state of the art science building with special glass and design features so birds would not strike its windows.
These stories are informative, but don't help backyard birders prevent window strikes. Backyard birders are often disappointed to hear the tell-tale thud of a bird striking a window in their home.
What can you do to avoid birds hitting your windows? Windows are invisible to birds. Lethal strikes have been documented by birds taking off from a perched position more than three feet from a window. Half of bird strikes are fatal, with the birds dying from head trauma. Window strikes occur year around and conservative estimates place the number of bird strikes in the U.S. alone at 100 million birds.
There is no one solution to this problem. Screens offer effective barriers (http://www.birdscreen.com" Target="_BLANK">http://www.birdscreen.com), and moving feeders within three feet of a window will save many birds. It will improve your viewing, too. Birds rarely hit a window when leaving a feeder within this distance; no fatal strikes have been recorded when feeders are placed this close to a home because a bird does not have enough momentum to hurt itself from this distance.
Placing electrostatic decals with outlines of leaves, birds, hawks or other opaque patterns on windows can keep birds from striking if the pattern is oriented vertically in columns separated by four inches, or in horizontal rows separated by two inches. Greater spacing reduces, but does not eliminate, all strikes. The more elements used the greater the protection. It's important to place the objects on the outside of the glass. Birds can't see the items when placed on the inside of today's double and triple paned glass. You can find these elements at specialty nature stores. Also, opaque film on windows can help prevent bird strikes (CollidEscape at http://www.flap.org" Target="_BLANK">http://www.flap.org).
Research into effective prevention is ongoing and includes studies on ultraviolet signals which birds see but humans can't.