How building and vehicle collisions kill and injure hundreds of millions of birds annually and what interventions reduce strike incidence.
Building glass collisions cause enormous welfare harm at both individual and population scale. Individual birds experience severe traumatic injuries from high-speed impacts including skull fractures, spinal injuries, and internal hemorrhage. Many do not die immediately but suffer for hours before death or predation. Prevention through window treatments that birds can perceive as solid barriers — collision-deterrent films, external screens, closely-spaced patterns — dramatically reduces strike rates. Lights Out programs during spring and autumn migration further reduce the catastrophic mortality that disoriented migrants face in illuminated urban areas.