Sheet glass and plastic in the form of clear and reflective windows are universally lethal to birds. Reasonable interpretation of available scientific evidence describes windows as a principal human-associated avian mortality factor that is an indiscriminant killer of common species as well as species of conservation concern. A conservative toll estimates 1 billion or more annual fatalities in the United States alone. The injury and death from birds striking windows are foreseeable and preventable, but the most promising legal measures and commercial products are not being applied or made available to protect defenseless victims. Avian window casualties are important for birds and people, and they have nonhuman animal welfare, biodiversity, sustainability, legal, and ethical and moral value justifying responsible human action. Preventing this unintended and unwanted lethal hazard for free-flying birds should be an obligation. Short-term solutions include retrofitting existing panes with a variety of proven measures that among others include applying various materials to cover the outside surface of windows. Long-term solutions include current and proposed bird-safe sheet glass and plastic for remodeling and new construction that have patterns that transform windows into barriers that birds see and avoid.
Keywords: bird–window collision prevention; collisions; wild birds; windows.