Window Collisions: A Silent Killer of Wild Songbirds

Glass windows kill between 100 million and 1 billion birds in the US alone every year, making building glass one of the leading human-caused sources of bird mortality.

Key Facts

Window collisions kill an estimated 100 million to 1 billion birds annually in North America
Second only to feral cats, windows are the leading source of direct human-caused bird mortality
Glass appears transparent or reflective — birds cannot perceive it as a barrier
Bird-friendly glass with ultraviolet-reflective patterns is visible to birds but not to humans
Simple tape strips or window films applied in a 5x10 cm grid pattern dramatically reduce collisions

Welfare Considerations

Birds that strike windows at full flight speed suffer blunt force trauma: fractured skulls, brain haemorrhage, internal bleeding and broken necks. Most die immediately; some linger for hours before dying from concussion and internal injuries. The scale of this mortality — hundreds of millions of individual deaths, many of migratory species already under pressure — represents an enormous welfare problem that is almost entirely preventable with inexpensive interventions at the building level.

What You Can Do

Apply bird-safe window markers to your most reflective windows in a 5x10 cm grid pattern
Install external screens or window films — these are most effective as they break reflections
Hang window feeders close to glass so birds cannot build flight speed before collision
Advocate for bird-safe building codes in your city for new construction
Report window collision hotspots to local bird organisations that maintain databases