Window collisions kill hundreds of millions of birds annually in North America and Europe, making glazed buildings one of the largest human-caused mortality sources for wild birds beyond habitat destruction and cats.
Window collision welfare is an area where simple, low-cost individual interventions can prevent significant bird suffering and death at scale. Each collision causes either immediate death or a period of concussion and pain before recovery or delayed death — welfare costs that are multiplied across hundreds of millions of events annually. The design solutions are well-developed and commercially available: external window films with visible patterns that birds can perceive as solid surfaces, external screens, and building design choices that reduce reflectivity and transparency. For existing buildings, applying external deterrent films to the most collision-prone windows identified through past observation is accessible and affordable. For new buildings, bird-friendly design certification should be standard.