How to Prevent Birds From Flying Into Your Windows

Birds hit windows because they take what they see in the glass for something they can fly into. The American Bird Conservancy (ABC) gives two causes: birds “perceive glass reflections of vegetation, landscapes, or sky to be real,” and they “attempt to reach habitat, open spaces, or other attractive features visible through” the glass. Read more about gifts for a bird lover. ABC and the Cornell Lab of Ornithology both give 2 inches as the spacing for markings on the outside of the glass.

Why Do Birds Fly Into Windows?

The Cornell Lab’s All About Birds says birds “typically crash into windows because they see reflections of vegetation or sky, or they see through the glass to potted plants or vegetation on the other side.” Cornell adds that collisions “can happen at any hour and any season, but are most frequent at dawn and dusk during spring or fall migration.”

The US Fish and Wildlife Service says birds can also hit windows “when they are attracted to landscaping outside the window or lights shining out from the interior.” Bright lights at night can disorient birds too: Cornell says the glow that office buildings and streetlights give off all night is “especially dangerous for drawing migrating birds off course.”

Can Birds See Glass?

ABC’s answer is that glass is undetectable to birds. People learn cues that signal glass, including window frames and door handles. ABC says birds “do not learn the same visual cues as humans,” and “as a result, glass is undetectable for them.” ABC adds that a bird may learn about one piece of glass through repeated interactions if it survives the first collision, but it cannot generalize from the experience and stays open to collisions with other structures.

ABC also explains why a strike is so dangerous: “Birds tend to collide with glass at high speeds and their small bodies, composed of hollow bones, leave them particularly vulnerable to injury.”

How Many Birds Die From Window Collisions?

Scott Loss and colleagues at the Smithsonian Migratory Bird Center and the US Fish and Wildlife Service reviewed 23 studies for a 2014 paper in The Condor. They estimated that between 365 and 988 million birds, with a median of 599 million, are killed each year by building collisions in the United States. Roughly 56 percent of that mortality was at low-rise buildings, 44 percent at residences, and less than 1 percent at high-rises. The Cornell Lab says a 2014 study put the toll from window strikes in the US at as many as roughly 1 billion birds a year.

The Guardian’s 2019 report on collisions in American cities says the Smithsonian’s migratory bird center estimated deaths at between 100 million and one billion birds annually. The US Fish and Wildlife Service says most fatal collisions take place at homes and at buildings under four stories.

Audubon says that each victim someone finds usually has three more that nobody sees, because those birds fly off and then fall out of view or get taken by predators. The Fish and Wildlife Service says many birds that hit a window look fine at first, yet most of them die later from traumatic injuries.

Which Windows To Fix First

ABC says a small number of problem windows often cause most collisions, so fixing the worst ones is an effective way to head off later collisions. It lists these windows to treat first:

• Windows where birds have already hit.
• Big windows and glass doors, above all ones that mirror habitat (sky included) or that let you see sky or plants through them.
• Windows that face bird feeders, bird baths, or plants that bear fruit.

Cornell adds big picture windows, two windows that meet at a right angle, and windows with feeders outside them. Its advice is to step outside and view your windows the way a bird would: “If you see branches or sky reflected in or visible through the glass, that’s what the birds will see, too.”

How To Mark The Glass

ABC says patterns of the right size and spacing, applied to the outside of the glass, can prevent most collisions. For stripes it gives a minimum width of one-eighth of an inch, and for dots or similar shapes a minimum diameter of one-quarter of an inch. It says the pattern should be easy to make out from 10 feet away, and that white patterns tend to perform best. The Fish and Wildlife Service gives the same size, a quarter inch or larger, with no more than 2 inches between marks, and says medium to light colors work best, since dark patterns are hard for birds to pick out when the glass is reflecting dark colors.

On spacing, the sources give slightly different numbers. ABC says the ideal spacing is the two-inch-by-two-inch rule, and that wider gaps endanger small songbirds, hummingbirds among them, which can fly through openings four inches wide. Cornell says to put decals an even 2 inches apart over all of the outside of the glass. Audubon’s 2014 tips say decals, temporary designs, and ribbons should be no more than 2 to 4 inches apart, because birds try to fly through any bigger gap.

Cornell says one or two stickers on a big window will not stop collisions. The stickers have to cover most of the glass and leave gaps too narrow for a bird to pass through.

These are the marking methods the sources name:

• Tempera paint or soap. Cornell says to mark the outside of the window with either, in a 2 inch by 2 inch grid or in any pattern or artwork. The Fish and Wildlife Service says non-toxic tempera paint is easily removed with vinegar and water.
• Cornell also lists decals, stickers, sun catchers, strips of mylar, masking tape, and even sticky notes, all stuck on the outer surface and spaced as above.
• Dot patterns and tape. Cornell says long-lasting tape products make it easier to apply the right spacing of dots.
• Cords. Cornell describes Acopian BirdSavers, closely spaced paracord that hangs down over a window, and says they can be spaced 4 inches apart because they are more visible. The Fish and Wildlife Service describes pieces of 1/8-inch paracord hung on the outside from the top of the window, with under 4 inches between them.
• One-way transparent film. Cornell says it lets people inside see out but makes the window look opaque from the outside.

ABC says to put these on the outside whenever possible: “Applied internally, the treatment is invisible to birds when window reflections outside are strong.” For a window that is hard to reach, ABC suggests a test. Put something large and bright, such as Post-It Notes, on the inside, then check the window from outside every two to three hours, beginning early in the morning. If you can clearly see the test solution, birds might too.

Screens And Netting

Cornell says mosquito screens work very well, provided they sit on the outside of the window and cover all of it. The Fish and Wildlife Service says external insect screens cut collisions by dimming window reflections and signaling to birds that windows are barriers.

The Fish and Wildlife Service says netting protects birds because they bounce off it instead of striking hard glass, and that the openings should be 1/2 inch or smaller so birds do not get caught. ABC says to install full external screens on new or replacement windows, even if the windows do not open.

Feeders Near Windows

The sources give two different pieces of advice. Audubon says that if you feed birds at home, place feeders and bird baths “either within three feet of windows, so birds can’t gather much speed before hitting, or more than 30 feet away.” Its 2014 tips say feeders should either attach straight to the window with suction cups or sit within 3 feet.

Cornell’s page says that older advice on safe distances for feeders outside windows is no longer considered valid, according to Christine Sheppard of ABC’s Bird Collisions Program. Sheppard is quoted: “If you’ve got windows near a bird feeder, you should make them bird friendly and don’t worry about how far away they are.”

Read more about putting out nesting materials for backyard birds.

Blinds, Curtains, And Lights At Night

Audubon says to draw drapes or blinds part way or fully whenever you can, particularly at night while lights are on inside, and to avoid placing plants near windows inside the home. A later Audubon article says closing blinds is less effective but is an easy way to cut collisions at least somewhat.

For new homes and remodels, Cornell lists external shutters kept closed when you are not in the room, external sun shades or awnings that block the reflection of sunlight, and interior vertical blinds with the slats kept only half open. Cornell also says to avoid visual paths to sky and greenery, and that shutting a window shade, or a door between rooms, can sometimes remove the look of a clear path through to the other side.

Turning off lights helps too. The Fish and Wildlife Service says switching off lights you do not need, by hand or with timers and motion sensors, can make glass less attractive to birds. Audubon says to switch lights off on nights of bird migration, and Rita McMahon of the Wild Bird Fund suggests alerts from BirdCast, a tool that sends alerts built on live radar data when many migrating birds are expected.

What To Do When A Bird Hits Your Window

Cornell says a bird that hits a window has the best chance of recovering if it gets help right away from a wildlife rehabilitation facility. It says victims of window collisions can have pain and internal injuries that do not show at first and get worse as time passes. Cornell’s steps for a dazed bird:

• Come up behind the bird and cover it gently with both hands. Small birds are very fragile, so do not close your fingers or hand tightly around the body.
• Place it in a small cardboard box lined with tissue or paper towel, or in a paper bag with no wax coating. Close the container and set it in a dark, quiet, warm spot away from children and pets.
• Once the bird is in the container, do not handle it or give it food or water.
• Find a rehabber near you and contact them for further instructions.

Audubon gives a fallback if you cannot reach a rehabber. Put the bird in a shoebox or paper bag in a quiet, dark room, away from pets and people, and leave it undisturbed for about an hour. Rita McMahon of the Wild Bird Fund says in that article that if you hear the bird tap-dancing around inside, it is feeling better, and Audubon says you can then carry it to your yard or a park and release it. Audubon adds that this does not guarantee the bird has recovered, since it has not had expert care. Audubon also says not to offer food or water, and warns that water poured down a bird’s throat can make it aspirate.

Read more about what to do if you find a baby bird on the ground.

Window Strike FAQs

Why does a bird keep pecking at my window?

Audubon says the bird is seeing its own reflection and trying to chase off what looks like a rival. Northern Cardinals and American Robins are known for fighting their own reflections, and this is common in both males and females. Cornell calls it “reflection aggression” and says it is most common in spring, when territorial behavior is at its height. Audubon says the behavior typically is not harmful to the bird, and Cornell says it is seldom a threat to the bird’s survival.

Audubon says to deter it you need to get rid of the reflection, and that the simplest way is to place something on the outside of the window, because the inside will not work. In the Audubon article, Eli Haislip of The Wood Thrush Shop says a sheet, blanket, or piece of cardboard hung over the window will work, and Audubon says you should be able to take the object down after a few days. Other experts in the article recommend an exterior screen or marking the glass with a bar of soap, and the article says decals made to prevent bird collisions can stop this behavior as well.

Do hawk silhouette stickers keep birds away from windows?

Cornell says hawk silhouettes do little to deter birds.

Do birds only hit windows during migration?

No. ABC says collisions in the US peak during spring and fall migration, and fall has the most. It also says dangers exist year-round, especially for glass near bird feeders and bird baths, that resident birds, juveniles above all, hit glass more often in summer, and that collisions also happen all winter long.

Read more about exotic pet bird care.

Sources

• American Bird Conservancy. “Why Birds Hit Glass.” abcbirds.org.
• American Bird Conservancy. “Solutions for Homes.” abcbirds.org.
• Cornell Lab of Ornithology. “Why Birds Hit Windows, and How You Can Help Prevent It.” All About Birds. allaboutbirds.org, and the archived copy: web.archive.org.
• US Fish and Wildlife Service. “Threats to Birds: Collisions (Buildings & Glass).” fws.gov.
• Audubon magazine. “You Found a Bird That Crashed Into a Window. Now What?” November 18, 2021. audubon.org.
• Audubon. “Help Birds Avoid a Deadly Collision.” July 29, 2014. audubon.org.
• Audubon magazine. “Why Birds Attack Windows and Mirrors, and How You Can Stop Them.” March 10, 2026. audubon.org.
• Audubon. “Reducing collisions with glass.” July 21, 2020. audubon.org.
• Loss, Scott R., Tom Will, Sara S. Loss, and Peter P. Marra. “Bird-building collisions in the United States: Estimates of annual mortality and species vulnerability.” The Condor, 2014. doi.org.
• The Guardian. 2019 report on birds killed by buildings in American cities. theguardian.com.

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