Birds strike glass because reflective or transparent glass is often invisible to them. It is estimated that between 100 million and 1 billion birds are killed by collisions in the United States alone each year, with an estimated 16 to 42 million fatalities in Canada.

As of early 2026, scientific estimates indicate that as many as 1 billion birds are killed by flying into windows in North America alone each year. This makes window collisions the second-largest human-related cause of bird mortality, trailing only predation by feral cats. While skyscrapers are often blamed, 99% of these fatalities actually occur at low-rise buildings and residential homes, where an average of two birds die per residence annually. High-value conservation efforts in 2026 emphasize the use of "bird-friendly" glass treatments, such as decals or vertical patterns spaced no more than 4 inches apart. These high-quality preventative measures are critical during migratory seasons, as exhausted birds are easily confused by reflected landscapes, turning a standard pane of glass into a deadly, invisible barrier for avian life.