Window collisions kill an estimated 600 million birds annually in the United States alone, making them one of the largest sources of human-caused bird mortality, and the problem is largely preventable.
Birds that strike windows suffer traumatic brain injury — they may appear dazed and recover, but many die from internal haemorrhage hours after the collision. Those that die instantly avoid prolonged suffering; those that survive the initial impact often experience significant pain and distress before death. Even survivors may suffer concussion effects that impair navigation, predator avoidance, and foraging for days. The scale of mortality — hundreds of millions annually in North America alone — represents an enormous aggregate welfare harm, concentrated especially during migration when billions of birds are in flight. Crucially, this is one of the most tractable bird welfare problems: simple, inexpensive window treatments dramatically reduce collision rates.