Window collisions kill an estimated 600 million birds annually in the US alone, making glass one of the leading human-caused mortality sources, with practical, affordable solutions available for homes and commercial buildings.
Window collision mortality represents one of the most tractable large-scale wildlife welfare problems: the cause is well understood, the solutions are proven, and implementation is achievable at individual, building, and municipal scales. Birds that survive initial impact may experience internal hemorrhage, head trauma, and delayed death from injuries not immediately apparent. The billions of individuals killed annually represent welfare harm of enormous scale. Retrofitting existing glass is cost-effective: exterior mosquito screens, adhesive dot patterns applied at 4-inch spacing, and commercial products like Feather Friendly markers provide significant protection. New construction adopting bird-friendly glass standards eliminates the problem at source.