Bird Window Collisions

It’s estimated that more than 100 million birds (both large and small species) die in the United States each year as a result of collisions with windows. Research has determined that birds can hit windows of all sizes at any height (from a one-story house to high-rise building), at anytime, day or night.

Birds in flight can hit windows with enough speed to be killed or stunned. Predators, especially domestic cats, often take birds not killed on impact.

Why Do Birds Hit Windows?

Many of the collisions occur when migrating birds fly into illuminated, high-rise buildings, especially on foggy or rainy nights.

In residential areas and office parks, windows often reflect nearby trees, shrubs, or sky. Birds don’t understand the concept of reflection. When they attempt to fly into the landscape they see, they strike the barrier they can't see—the glass.

A bird being pursued by a predator will sometimes fly into a window. Sharp-shinned hawks and cooper's hawks prey on small birds and have learned to hunt in yards with bird feeders.

Preventing Window Collisions

In partnership the City of Boston and leading building owners and managers, Mass Audubon supports Lights Out Boston. The goal is to encourage building managers throughout the city to turn off architectural and window lighting overnight during the spring and fall migration seasons to help protect migratory birds and save energy.

In addition, there are several things a homeowner can do to prevent window collisions.


Window strikes frequently follow a pattern. You may find dead or injured birds repeatedly beneath the same window and at certain times of day. To determine what birds see in the reflection, place yourself directly in front of the glass. Repeat this at different times of the day to view the window's reflection under different light conditions.

Watch feeders and birdbaths to ascertain whether birds are colliding with windows as they fly from those locations. If this is the case, most researchers agree that the feeder should be moved closer to the window. Birds, flying from a feeder that's only 2 or 3 feet away from the glass rarely get up enough speed to kill themselves.

Break up the reflection

You can use any decals or stickers that are at least 6 inches in diameter to alert birds that they’re in an unsafe flying zone. Make sure to place several on the outside of the window, one foot apart, both horizontally and vertically. Some decals contain a component that brilliantly reflects ultraviolet sunlight. When placed on the outside of the window, this ultraviolet light is invisible to humans, but glows brilliantly for songbirds.

Provide an impact-absorbing barrier

You can cover windows with screen that affixes to the glass using hooks or suction cups. This reduces the reflection and prevents injury by cushioning the bird if it inadvertently flies toward the window. It also prevents territorial birds from attacking their reflection in the glass.

Helping an Injured Bird

When a bird hits a window, swelling in the brain may temporarily incapacitate it. If there are cats or other predators nearby, place the bird in an enclosed box or under a colander to keep it safe.   

Handle the bird as little as possible and do not attempt to give it food or water. As the swelling subsides and the bird becomes more active, you may release it. If the bird doesn’t recover, you’ll need to enlist the help of an expert. Read more about helping injured birds. Learn More