Collision with glass is believed to be one of the principal man-made causes of death for birds in North America. It is estimated that between 300 million and 1 billion birds are killed annually in North America by collisions with buildings – primarily by striking windows. Last year alone the Wisconsin Humane Society admitted more than 200 birds who were involved in window collisions.
Birds simply cannot tell the difference between reflection and reality.
Make the glass visible to birds. One way to achieve this is to apply something to the window to provide contrast. ABC Birdtape is one such product.