Investigations into How to Prevent Deadly Bird Window Strikes

Photo © David Schiersner

Among the greatest sources of human-caused bird mortality in the United States are windows. Some estimates put the number of deaths as high as one billion annually (roughly equivalent to a full 9% of the bird population)open_in_new. Much of this is the result of commercial, rather than residential, windows; but, it is still critical to learn as much as you can about how to prevent window strikes in your own home. You can work to mitigate this potential ecological trap where you live, and act as a community advocate to help commercial properties embrace best practices for decreasing bird-strikes on their large, heavily-glassed buildings.


Photo © eatyourchildren

No one wants to live and work in windowless fortresses. Windows are critical for improving light quality, air quality, and giving us visual access to natureopen_in_new. They also mean we have to use less electricity to heat and light a building, making windows a sustainable choice for new construction. Since we don’t want to get rid of windows entirely, we have to embrace adaptations that mean we can keep them, and our birds too.


Photo © elitatt

What do we know about how to prevent window-strikes? Not a ton, but glass is an indiscriminate killer, it kills healthy birds along with sick ones, rare ones alongside common onesopen_in_new. Juvenile birds, often less experienced than their older counterparts, seem to be more likely to suffer from a window strike as wellopen_in_new. Techniques to prevent fatal window-strikes range from physical barriers to adhesive films and decals to speciality glass; but so far, we don’t have a universally applicable solution.

Treating injured birds

If you find a stunned or injured bird the best thing you can do is put it someplace safe in a cardboard box and call a local rehabilitation professional, who has some tricks up their sleeves for helping birds with head injuries, or broken bones.


Photo © Florida Bird Pictures

There are a handful of researchers trying to improve our understandings of best practices when it comes to windows and birds. In an urban landscape in northwestern Illinois, a study of 20 buildings correlated the number of window strikes with the size of the window. Larger windows tended to be responsible for more birds strikes. They also found that the patchy habitat in urban areas, with clusters of wild space where birds congregate, may contribute to higher numbers of window strikes because the birds were dispersed among buildings and moving between patches as a part of their daily livesopen_in_new. While the structures the research focused on were larger, this may give pause to homeowners who create attractive habitat in their yards, inviting them to look at their yards with a bird’s-eye view towards movement around and through the habitat they create, their neighbors’ yards, and particularly risky windows.


Photo © CameliaTWU

A study from Duke University looked at six buildings on their campus to find out which ones were responsible for the greatest number of bird strikesopen_in_new. Using a series of 21 day surveys conducted from spring 2014-spring 2015 they counted the number of bird carcasses found at the foot of each building. They found not only that greater window area was correlated with more fatal bird strikes, but that the more forested area surrounded the building the more likely birds were to hit the windows.


Photo © BeestFace

Potentially of the most interest from the Duke research was that one building, despite having a huge glass facade and extensive adjacent forest, had only two bird strikes. What might have accounted for this exception? That particular building used etched, or fritted, glass, with closely spaced lines or dots that help make it visible to birds. You can see an example of fritted glass in the image above.


Photo © Thomas Hawk

In a five year survey surrounding the California Academy of Sciences building in Golden Gate Park, San Francisco, staff counted dead birds around the building each morningopen_in_new. The researchers found 308 dead birds over the course of the multi-year study. Large windows were disproportionately responsible for fatal bird strikes, but simple mitigation measures like mullions (the metal bars seen in the image of the California Academy of Sciences building) seemed to lessen the likelihood of strikes.


Photo © Aaron Maizlish

The same research included surveys of the birds in the park to determine which birds and at what abundance they were found in the surrounding vicinity. The Prothonotary Warbler captured in the image above (usually only found in the Eastern half of the U.S.) was a very unusual visitor to the Golden Gate Park. More common visitors, along with this unusual find, were documented in the bird survey. When they compared the birds in the area to the birds that had suffered window strikes they found that males, migrants, and juveniles were more likely to be victims of windows. Small birds, like Anna’s hummingbird, which accounted for 42% of all fatal window strikes, seemed particularly vulnerable. The museum has subsequently installed window shades and dramatically reduced the number of window strikes at the facility.

Pro-tip: Check-out the bird surveys conducted by the California Academy of Sciences perimeter bird surveys

This research used eBird to collect data about the birds found in the areas around the Cal Academy. You can browse their lists, and see other bird reports in Golden Gate Park.

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Photo © Darren Graffuis Cornell University Department of Landscape Architecture YardWorks

Start by identifying dangerous windows. Large picture windows or a pair of windows at right angles to each other on the corner of a house or other building are usually the worst culprits. Remember from above that patches of vegetation adjacent to windows are correlated with strikes. It makes sense to look at your windows from a bird’s point of view. Imagine flitting around the yard, and if you see branches or sky reflected in or through the glass, that’s what the birds will see, too. The image above is a rendering of how a bird might move around a residential yard. It is fun to imagine yourself from their perspective and find the windows that you can target for intervention. Adding beautiful decal patterns, stickers, or simply drawing the shades seem to be helpful interventions you might employ.

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Photo © Stan Lupo

Without even changing your windows, you might be able to reduce mortality, at least by resident birds, by moving your feeders and birdbaths to new locations. Bird strikes are significantly more likely to be fatal when birds take off far enough away from the window to be flying at top speed when they hit. When feeders are placed within 3 feet (one meter) of window glass, or affixed to the window or frame, birds may still fly into it, but seldom with enough force to injure themselves.

Treating windows

For ideas on how to treat your windows to minimize bird strikes, visit American Bird Conservancy. All recommended window products have been tested for effectiveness.