Biggest cause of bird mortality: window strikes

Kenai National Wildlife Refuge photo Reflection of the surrounding vegetation is likely the number one reason why birds, such as this Steller's Jay, fly into windows.

It always happens on a Friday afternoon around 4:25. Computer is shutting down, projects not finished are piled to the side, and the weekend is calling. Just as I begin to shed the uniform and turn my thoughts to golf, the phone rings and the caller reports that a bird has struck their window and lays stunned in the yard. I agree to pick up the bird on my way home and am saddened to hold the warm lifeless body of an adult male pine grosbeak. I take a moment to look for bands, signs of disease, or any unusual circumstances. None found, so the case is closed and the weekend proceeds.


This may seem cold, but it is a scenario played out dozens of times over the years. It has become such a common occurrence that I have lost most of the emotion that normally comes with the senseless loss of such a beautiful bird. We get lots of reports, but I always wondered how many birds meet their demise in this fashion.

A recent study by a University of Alberta biology class has finally put a number to the question of how many birds are killed by window strikes each year. First, they solicited the help of 1,700 volunteer home owners who could search daily and report the number of bird fatalities at their homes. The researchers then applied the number of window strikes to the number of homes in their region and ultimately to all homes in Canada.

While there are likely flaws and errors in the study design, one point is very clear. Lots of birds succumb to window strikes. When extrapolated over all of Canada, the class came up with 22 million birds killed annually. The U.S. population is roughly 10 times that of Canada and it is likely that the number of window strikes follows a similar trend. I saw educated guesses that put the North American total at over 1 billion annually! A quick search of the census records indicates there are over 130 million houses in the U.S.

There are many different causes that lead to birds hitting windows. The two major culprits are feeders and the season. Feeders placed too close to a window are often a major contributor to bird window strikes. Also, during fall migration, there are millions of young and inexperienced hatchlings flying around and inevitably they will bump into windows. If they are going fast, this can be fatal.

Here are a few simple hints that can significantly reduce your role in this problem. To reduce the bird feeder problem, move the feeder further away from large windows or move it very close. Feeder birds get spooked a lot and in their rush to flee they run into windows. If it is very close, they don’t build up enough speed to do critical damage. A good pair of binoculars will still allow you to enjoy viewing the activity at your feeder from 30 or more feet.

The other major fix involves disrupting the reflection from the window. Birds see the reflection of sky or trees, and head right into the glass. Breaking up this reflection can be as simple as placing a few strips of tape, perhaps more aesthetically-pleasing static-based stickers, or putting screen or mesh over the glass. There are several creative suggestions out on the internet, but I don’t know the validity of their effectiveness. Birds are able to see into the ultra-violet (UV) spectrum. Reportedly, UV highlighters can be used to draw a net on the outside of the glass. If you use a pale yellow color it will be undetectable to human viewers, but will look like a brilliantly-colored mesh to the birds. One problem is that rain washes it away and it has to be reapplied.

Whatever method you choose, think about how little effort it would take to reduce the window strikes at your house. If you get multiple strikes on the same window, it’s probably time to figure out what is causing the birds to run into the window and see what you can do to fix it. With over 140 million homes in the U.S. and Canada, it only takes a few window strikes at each house before we are putting a huge hurt on North America’s bird populations.

Todd Eskelin is a Biological Technician at the Kenai National Wildlife Refuge. He specializes in birds and has conducted research on songbirds in many areas of the state. You can find more information about the Refuge at or


Fri, 06/22/2018 - 00:03

Tsalteshi Sprockets teach youth cycling