Window collisions kill an estimated 1 billion birds annually in North America, making them one of the leading human-caused sources of bird mortality — and one of the most preventable.
Birds that collide with windows experience acute trauma — concussion, broken beaks, spinal injury, and internal hemorrhage. Many do not die instantly but lie stunned on the ground, vulnerable to predation and unable to regulate body temperature. Even birds that appear to recover may die from internal injuries hours later. The welfare scale of window collision mortality — a billion individual trauma events annually — is difficult to overstate. Every house, office, and school building with uncovered glass is a potential hazard.