Glass windows cause an estimated billion bird deaths annually in North America alone, making window strikes one of the largest human-caused sources of bird mortality and suffering.
Window strikes cause two categories of welfare harm: immediate death from impact trauma, and protracted suffering from brain injury in birds that survive the initial strike but die over subsequent hours. Both categories involve enormous numbers of individual animals experiencing preventable harm. The solutions are well-established: bird-safe glass with UV patterns, external screens, and window films are effective and increasingly affordable. The barrier to uptake is primarily awareness -- most householders do not know that their windows kill birds, or what they can do about it. Building codes that incorporate bird-safe glazing standards for new construction would prevent millions of deaths annually with minimal additional cost.