Migratory Bird Flyways and Building Collision Mortality

Window and building collisions kill hundreds of millions of birds each year along migratory flyways, making glass-related mortality one of the largest anthropogenic threats to bird populations.

Key Facts

Estimates suggest 600 million to 1 billion birds die from building collisions annually in the United States alone
Glass is invisible to birds, which perceive reflections of sky and vegetation as continuation of habitat
Peak mortality occurs during spring and autumn migration when billions of birds move through urban areas
Lights-out programmes during peak migration can reduce mortality by up to 70 percent for nocturnally migrating birds
Bird-safe glass with ultraviolet-reflective patterns visible to birds but not humans is now commercially available

Welfare Considerations

Birds killed in window collisions typically suffer acute trauma injuries including brain haemorrhage, broken necks, and internal bleeding. Injured birds that do not die immediately may suffer for hours before death. The scale of suffering across all collision victims globally is enormous but largely invisible to the public, as most collisions happen at home windows or office buildings and victims are quickly removed by scavengers. Simple interventions including window films, external screens, and building light reduction during migration have been demonstrated to dramatically reduce mortality.

What You Can Do

Apply bird-deterrent window film or screens to glass windows at home
Turn off non-essential building lights during peak spring and autumn migration nights
Support municipal lights-out ordinances for commercial buildings during migration
Donate to bird collision monitoring and response organisations in urban areas
Advocate for bird-safe glass requirements in new building construction codes