Reducing collisions with glass

Creating Visual Cues

The Issue

Birds face innumerable threats in our human built environment and our glass surfaces are one of the biggest. During daylight hours, birds collide with reflective surfaces when they stop to feed or rest, when avoiding a predator or flying from tree to tree. 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.

The Impact

Window collisions are one of the leading direct human causes of bird mortality. A 2014 study by the US Fish and Wildlife Service and the Smithsonian Institution estimated that between 365 million to one billion birds are killed annually by building collisions in the U.S.


  • Minimize unnecessary bird deaths
  • Support your organizations sustainability goals
  • Receive recognition for sustainable, bird-friendly practices
  • Be recognized as a regional and national leader in sustainability and bird conservation


People ‘see’ glass because we understand buildings. Birds need strong clues on or around glass to warn them that it’s there.

Reducing reflective surface collisions

  • Create patterns on reflective glass surfaces (quantity and spacing matter: multiple markings 2 to 4 inches apart are recommended)
  • Install external screens on windows
  • Close blinds or curtains
  • Move interior plants away from windows
  • Place bird feeders directly on windows


Bird-building collisions can happen at any time of the day and year but tend to increase during migration and when young birds start flying. Therefore, the most crucial times for these measures are during spring and fall migration and in the breeding season in  your area.


Resources and Videos

Download a two-page fact sheet that has an overview of the issues and what people can do to help.

See a sampling of bird-window collision prevention methods with relative costs and download a brochure with recommendations on Making Your Windows Safer for Birds, produced by the Bird-Window Collision Working Group (BCWG),  a collaboration between The Acopian Center for Ornithology, Muhlenberg College, Lehigh Valley Audubon Society, Wyncote Audubon Society, and Audubon Mid-Atlantic.

Additional collision prevention resources are available on our Lights Out page.