In the fall of 2023, 1,000 birds died overnight at a glass-fronted building overlooking Lake Michigan. Hundreds of warblers, including Palm, Yellow-rumped, and Tennessee collided with the building, along with scores of Swamp, White-throated, and Lincoln's Sparrows, and buntings, Soras, and thrushes. The mass die-off prompted national attention and calls from American Bird Conservancy (ABC) and other organizations for the building owners to act swiftly to address the problem. The call was heeded, but scores of other buildings still need to follow suit. 

Migration, sadly, brings bird deaths from window collisions in large numbers (more than 1 billion birds die from window collisions in the U.S. every year), but the threat doesn't stop with migration. It isn't just migratory birds or birds navigating a labyrinth of glass-encased skyscrapers that are at risk. All too often, it's birds in backyards that become collision victims.

A Problem Close to Home

In January 2025, reports were made to the U.S. Geological Survey's Bird Banding Lab of not one, but two banded Northern Cardinals that struck the same window of a residence on the same day. The female banded in late winter 2023, and the male banded in fall 2024, were both banded at a nearby banding station in Illinois and died because of the collision with this glass window. These birds were both under 2 years of age.

Another Northern Cardinal window collision victim was reported to the BBL several years before. This cardinal struck a window adjacent to bird feeders at a residential home in Cambridge, New York. Banded only seven months prior in Belknap County, New Hampshire as a hatch year individual, this male cardinal sadly died before reaching its first breeding season. These are just a few of many encounter reports received at the BBL for banded birds that have collided with glass. 

Since 1922, the BBL has amassed nearly 11,000 reports of banded bird collisions, including more than 900 reported in the last five years alone. Given how rarely window collision victims are detected and reported, this is an astonishing number. Many birds reported after building collisions are species, like cardinals, that frequent bird feeders, particularly during the winter months. Other species commonly reported after window collisions include Evening Grosbeak, Purple Finch, Mourning Dove, American Goldfinch, and Common Grackle, as well as raptors such as Sharp-shinned and Cooper's Hawks that utilize feeders to hunt for smaller passerines.

While some collision victims are banded, many are not. Any banded bird that collides with glass provides a small glimpse at the serious problem of window collisions, as well as vital information for that bird individual and species, revealing seasonal and temporal patterns in survival and habitat use, as well as migratory pathways.

Many people assume bird-window collisions are caused by skyscrapers in city centers, but all structures with windows put birds at risk. In fact, an estimated 44 percent of window collisions occur on residences only one to three stories high. The story of this Northern Cardinal shows that windows at home can be just as deadly.

What Causes Collisions?

Birds collide with windows because they see habitat through the glass or reflected back at them — they don't experience glass the way people do. People don't see glass either, but when we see a window sill or a doorframe, we know to interpret these as cues that glass is present. Without those visual markers, we're likely to bump into glass, too. 

Birds don't see those markers the way we do, and this makes glass a danger. For us, colliding with glass may result in bruises (to our bodies and sometimes our egos), but we recover. By and large, birds do not. And while it may be comforting to think that birds that collide with windows can simply “shake it off,” new research is indicating that is not the case. They collide at high speeds and their fragile bodies make them more vulnerable to injury. Even with intensive care from experienced wildlife rehabilitators, birds that collide with windows frequently succumb to their injuries. 

Collisions are a year-round problem. In late spring and summer, juvenile birds are busy exploring their environment. In winter, when resources become scarcer, resident birds must cast a wider net and expand their territories to find food. This increased activity adds to the likelihood of a bird colliding with a window.

Heading Off Collisions at Home

Whether you live in a farmhouse in the country, a condo in a suburb, or an apartment block in a city, your home is part of the habitat birds need to survive. Treating your windows to prevent collisions goes hand in hand with other actions to help birds, like keeping cats indoors, planting native plants that provide food, and passing on pesticides. 

Bird feeders and bird baths can be a helpful way to support birds through harsh winter weather. Varying advice has been given about the optimal distance between bird feeders and windows, but the fact is, unless your windows have been treated to prevent collisions, there's no such thing as a safe distance. Even in the absence of feeders or other features like native plants that would draw birds closer to your home, you should have a plan for treating your windows. And if you're planning on feeding birds, taking care to reduce collisions is a must. 

ABC's Collisions team has tested dozens of products for their efficacy in reducing collisions and minimizing risks to birds. Our Solutions Database provides reviews of every product we've tested along with approved products and solutions for residential homes or businesses. We offer solutions for retrofitting existing windows or installing new windows, with options ranging from low-tech tempera paint patterns to customized etched glass installations. If you can't address every window, prioritize large picture windows, windows near bird feeders and baths, and windows where collisions have previously occurred. 

The results of collision mitigation efforts are immediate. Donna Barski, an ABC member and participant in Project FeederWatch, was getting about one window strike a week. Using ABC's recommendations, she bought tape and applied it to her windows. Now, Barski says collisions have stopped entirely. 

“As far as the aesthetics? My husband and I have no trouble viewing the birds and we actually find the stripes do not inhibit our view of the outside at all,” Barski said. “In fact, they actually are a pleasing addition, especially knowing that they have such an important function.“

How to Help a Window Collision Victim

Bird-friendly window treatments aren't foolproof, though they can drastically reduce collisions. If a bird does collide with a window, it needs to be seen by a wildlife rehabilitator. Even if it appears fine, the force of collisions can cause severe internal injuries. With avian flu circulating at high levels at the time of publication, it's important to take the extra step of checking on and following advice from your local wildlife authorities. Be sure to take proper precautions when handling birds: Always wash your hands thoroughly for at least 20 seconds using soap and warm water before and after, and wear a disposable mask and gloves if handling sick or dead birds. Follow these steps for handling injured birds:

• Pick up the bird. Approach from behind and gently cup your hands over the bird. Hold it securely without squeezing — birds' bodies are extremely fragile. Avoid handling the bird any more than is necessary to minimize stress. 
• Place the bird in a container like a small cardboard box or paper bag. Putting a paper towel on the bottom helps the bird get a grip. Keep the bird in a quiet, dark place.
• Don't feed the bird or attempt to give it any water. 
• Contact a wildlife rehabber for further guidance. 

To report a bird band to the USGS Bird Banding Laboratory from a bird that has collided with glass, please submit it to reportband.gov. Be sure to indicate that the bird struck a building or window in the “How Obtained” data field and provide any additional information about the area in the remarks (residential or urban building, the presence of feeders, etc.). The USGS is currently exploring how we may add to the science of understanding bird collisions through the data collected from the BBL database.  

This article was written in partnership with the U.S. Geological Survey's Bird Banding Lab.