Window Collisions and Wild Bird Welfare

Window and glass collisions kill an estimated 100 million birds annually in the US and millions more globally, making glass a significant but largely invisible cause of bird mortality.

Key Facts

Birds cannot perceive glass as a barrier — they see reflected sky or habitat and fly into it at full speed
Glass-related bird strikes peak during migration when birds are moving through unfamiliar areas in dense numbers
External window markers visible to birds reduce collisions by 50-80% in controlled studies
Birds that survive strikes often die hours later from internal injuries or brain trauma
Internal building lighting visible through glass at night attracts migrating birds causing collision risk

Welfare Considerations

Window collisions are one of the most commonly overlooked causes of bird welfare harm, precisely because they occur in individual incidents that are not visually associated with human activity. A bird found dead or stunned beneath a window has suffered a traumatic impact that may include broken wings, brain trauma and internal injuries. Survivors frequently die from delayed effects of their injuries. The scale of this harm — 100 million US deaths annually — represents a genuine welfare crisis hidden in plain sight at every glass-containing building. The solutions are known and effective: external window markers, bird-friendly glass design, and reduced nighttime interior lighting. Implementation is simply a matter of awareness and will.

What You Can Do

Apply external window markers or bird-friendly film to large windows and glass doors at home
Support bird-friendly building design standards in planning applications for new glass-fronted buildings
Turn off unnecessary interior lighting visible through glass at night during peak migration seasons
Report bird strike locations to BTO to contribute to mapping of collision hotspots