Window strikes kill up to one billion birds annually in North America alone, making building design and glass treatment a significant and tractable bird welfare intervention.
Window strike welfare operates at both the individual and population levels. For individual birds, a window strike causes acute trauma ranging from stunning to death, with many birds dying from internal injuries hours after an apparently minor collision. At the population level, window strike mortality of up to a billion birds annually in North America represents one of the largest human-caused wildlife welfare harms, comparable in scale to cat predation. The individual welfare response includes keeping cats away from known strike areas and providing appropriate first aid for stunned birds. The systemic response involves changing the visual properties of glass through patterned film, UV-reflective coatings, and exterior screens, combined with lights-out programs during migration season that reduce the attraction of migrating birds to illuminated buildings.