Glass windows are bird killers. Here's how you can help.

New York City just passed legislation requiring bird-friendly glass in all new buildings. Here's how individuals can help too.

December 13, 2019 

Glass windows kill close to a billion birds a year

When a human walks into a glass door, usually the worst that happens is a bruise or some loving ridicule. But when a bird flies into a glass door or window, they probably die. A 2014 study estimates that glass windows kill close to 1 billion birds yearly. Behind free-ranging cats, it’s one of the deadliest man-made threats to birds.

That tale-tell thunk of bird on glass is familiar to most of us. Glass windows reflect outside vegetation and birds will dive headlong into what looks like a safe place to fly. Some fly away afterward, but they don’t last long, said ornithologist Brian O’Shea, collections manager at the North Carolina Museum of Natural Sciences.

“Bird skulls aren’t built to hit windows,” he said. “They aren’t flying around with helmets on their head.”

Studies have found that low-rise buildings (56 percent) and residential homes (44 percent) kill the most birds. O’Shea says bird feeders close to windows make things worse by increasing the amount of birds near homes and buildings, and the chances that they’ll fly into windows. A hawk decal on the window doesn’t help. “Birds just fly around those,” said O’Shea.  

Preventative measures 

Preventing bird window collisions sounds straightforward: increase the amount of visual “noise” on your window so that birds perceive it as a barrier.

Adding barriers to the outside (rather than the inside) of windows is most effective, because glass acts like a mirror. Some examples include window shades, sunscreens, fritted glass and painted patterns. The trick is creating a tight pattern—vertical lines no more than 2 inches apart and horizontal lines no more than 4 inches apart.

But for those of us that like an unobstructed window, UV-reflective glass is an option because birds can see UV light, and we can’t.

These interventions are starting to catch on. New York just became the largest city to pass rules requiring “bird-friendly” glass in all new buildings, joining San Francisco and Oakland, CA. 

But for existing windows, the American Bird Conservancy recommends these products:

For more information on how to help birds check out these guides: