Glass windows and buildings kill an estimated billion birds annually in North America alone. Prevention through simple modifications can dramatically reduce this source of bird mortality.
Window strikes cause both acute death and injury welfare problems for wild birds at enormous scale. Birds surviving the initial impact often suffer from internal haemorrhage, brain injury and disorientation that makes them vulnerable to predation. The welfare harm of window strikes is almost entirely preventable through building design and modification. The critical deterrence principle is that markings must be spaced sufficiently close — within 5cm horizontally and 10cm vertically — that birds perceive a barrier rather than gaps through which they can fly. Single decals or widely spaced markings are largely ineffective. Retrofit solutions including external films, screens and decals are cost-effective for existing buildings. New buildings in areas of high bird migration should incorporate bird-safe glass as a standard element.