Sticking one or two decals on a window will not help. You might try one of these techniques, ranked roughly from most to least effective: Cover the glass on the outside with window screening or netting at least 2–3 inches from the glass, taut enough to bounce birds off before they can hit the glass.

What is WindowAlert? WindowAlert is a collection of bird-saving products designed to eliminate collisions of birds with windows. Our non-adhesive, static decals reflect the ultraviolet sunlight producing a glowing effect for birds. What looks like a transparent sticker to us will appear as a glowing object to them.

Vertical stripes or patterns (at least 1/4 inch-wide, maximum spacing of 4 inches), or horizontal stripes (at least 1/4 inch-wide, maximum spacing of 2 inches) are effective at preventing window collisions for most birds (see the last image).