In the United States alone, it is estimated that each year during
migration, millions of birds fly full tilt into windows and are
seriously injured or killed.

You can minimize these collisions by breaking up the reflection on the
outside of the window with a window screen, flash tape and bird netting.

Life-size, animate "scares" (plastic falcons, owls and balloons) and
falcon or owl silhouettes attached to windows with suction cups are not
effective deterrents.

Planting trees and installing window awnings to block the sun from
hitting the window may eliminate some reflection.

Migration isn't the only time homeowners have trouble with bird-window
collisions. Birds may hit your windows during breeding season, when they are leaving bird houses and bird feeders you provided them, and in
the winter too.

During breeding season, male cardinals, woodpeckers and mockingbirds may
" fight" their own reflections in windows (and car mirrors). They'll stop
banging into the window as the breeding season ends. You can discourage
them with screens and other barrier techniques.

Regardless of the season, birds can fly into windows when they're
frightened while visiting a feeding station. Either move the feeders a
considerable distance away from the window, or immediately adjacent to
the window (so birds don't get up to flight speed before hitting the
window).