Window strikes kill hundreds of millions of birds annually in the US alone. Understanding why birds hit glass and how to prevent it offers straightforward opportunities to reduce this widespread welfare harm.
Bird window strikes represent a massive welfare harm distributed across millions of ordinary homes and buildings. The individual welfare impact of each strike varies - many birds die immediately from head trauma, others suffer prolonged injury before dying, and survivors may have lasting neurological impairment. The scale makes this one of the highest-impact preventable sources of bird mortality in the built environment. The welfare challenge is awareness: most people never connect their reflective windows with the dead or stunned birds occasionally found outside. Simple, inexpensive interventions are highly effective and require only the motivation to implement them. The welfare case is reinforced by conservation significance - window strikes disproportionately kill certain species and remove experienced adults during migration, affecting population dynamics.