Preventing Window Strikes: What Actually Works

Why birds hit glass

Birds do not perceive glass as a solid surface. During the day they see the reflection of sky, trees, and open space and fly toward it at full speed. At night, lit interiors disorient migrating birds and pull them toward buildings. Collisions with residential and low-rise buildings account for an enormous share of annual bird mortality in North America, and most of it happens at ordinary homes rather than skyscrapers.

A stunned bird that flies off is not necessarily fine. Many collision victims die later from internal injury or predation while disoriented.

The 2 x 2 rule

The current standard is to break up the reflection with a visual pattern spaced no more than two inches apart horizontally and two inches vertically. Birds will not attempt to fly through a gap that small. Older advice used a four-by-two spacing; two-by-two is the conservative figure now recommended because it also accounts for small species like hummingbirds and kinglets.

The pattern must be on the outside surface of the glass. Anything applied inside sits behind the reflective layer and the bird never sees it — which is why a single hawk silhouette decal stuck to the inside of a window does essentially nothing.

• Exterior dot or stripe tape applied in a 2 in grid.
• Paracord or bird-safe curtains hung vertically 4 in apart across the outside of the glass.
• Exterior insect screens — they eliminate reflection and cushion any impact.
• Tempera paint or a bar-soap grid drawn directly on the outside of the glass — free, effective, washes off.
• Etched, fritted, or patterned glass if you are replacing windows anyway.

Feeder placement changes the physics

Place feeders and baths either within three feet of the glass or more than thirty feet away. Close in, a startled bird cannot build up enough speed to be injured. Far out, a fleeing bird has room to see and avoid the window.

The distance to avoid is the middle range of roughly five to twenty feet, which lets a bird reach full flight speed before it reaches the glass. Moving a feeder eight feet closer to the house sometimes ends a collision problem by itself.

Night lighting

Turn off or shield unnecessary exterior lights during spring and fall migration, and close blinds on lit rooms after dark. Use downward-facing, shielded, warm-color fixtures where outdoor lighting is required. This matters most in April through May and August through October, when night-migrating songbirds pass overhead in large numbers.

If a bird strikes your window

Approach calmly and place the bird in a ventilated cardboard box lined with paper towel. Keep it in a dark, quiet, warm place indoors and away from pets. Do not offer food or water — an injured bird can aspirate and drown.

Give it thirty minutes to an hour, then take the closed box outside, open it, and step back. A recovered bird will leave immediately. If it cannot fly, or if you see a drooping wing, bleeding, or a head tilt, contact a licensed wildlife rehabilitator. Handling wild birds beyond this kind of brief rescue is regulated in most jurisdictions.