Glass windows and buildings cause approximately one billion bird deaths annually in North America alone.
Window strikes cause immediate death, brain injury, internal haemorrhage, and injured birds that die slowly from their wounds. Those that survive the initial strike often succumb to predation while disoriented. The scale of this mortality represents one of the largest human-caused threats to bird populations. This is a welfare problem that affects billions of individual animals and one where individual and policy action can make real differences.