Glass windows and buildings kill up to one billion birds in North America alone each year, making window collisions one of the leading human-caused sources of bird mortality.
Window collision victims experience acute trauma — broken beaks, skull fractures, internal hemorrhage, and spinal injury. Birds that appear to fly away after a strike often die hours later from brain swelling. Migratory birds are already physiologically stressed from long-distance flight; collision injury compounds this. Even non-fatal strikes leave birds vulnerable to predation during recovery.