Most migratory birds travel by night, to avoid the heat of the sun, thermals that destabilize the environment, and predators. Because they are attracted to and disoriented by artificial lighting that draws them into unsafe areas, reducing light pollution is an important factor in minimizing window collision mortality.

Shiny glass exteriors, internal plants near windows, glass corners, and greenery close to buildings can all be deadly as birds are unable to distinguish reflection from open flyway. For every collision victim found, three more typically go unseen, flying out of sight before falling or being carried away by predators.

Collisions with built structures are a primary source of bird mortality, killing hundreds of millions of birds annually in North America alone. North America has lost nearly one-third of its birdlife in the last half-century, with migratory species experiencing particularly acute declines.