Window collisions kill an estimated 600 million birds annually in the US alone, making this one of the most significant human-caused sources of wild bird mortality and welfare harm.
Window collision welfare involves both immediate death and delayed mortality from internal injuries sustained in collisions. Birds that fly into windows often suffer concussion, internal hemorrhage, and skeletal injuries that cause suffering before death hours to days later. The scale of the problem - hundreds of millions of birds annually in North America alone - makes this one of the largest quantifiable welfare harms caused by human infrastructure. The welfare opportunity is substantial: simple, low-cost interventions at the household level can dramatically reduce collision mortality, and building design standards for bird-friendly glass are increasingly being adopted in major cities.