Windows: A Clear and Present Danger

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We often see birds colliding with windows, buildings, and other large structures in cartoons and video games. This is a fairly common comedic trope, but the sad reality is that these accidents are actually a serious problem. Care to take a guess as to how many birds are injured due to collisions with windows each year? It’s estimated that about 1 billion birds are killed each year as a result of colliding with a window. (i) Last year at the Bird Center, a little under 10% of diagnosed bird injuries were a result of colliding with a window/building. Not every collision is preventable, but there are numerous steps that we all can take to keep our feathered friends safe from a danger that’s practically invisible to them.

Collisions can happen both during daytime and nighttime. Collisions that occur during daylight hours can result from a multitude of scenarios, such as birds needing to quickly leave a feeder that’s too close to a building. By contrast, nighttime incidents are most commonly associated specifically with migrating birds. (ii) Researchers haven’t been able to explain why, but nighttime migrating birds seem to be attracted to light that is reflected off of or coming out of windows at night. The exact reason for this phenomenon isn’t totally understood at this time, but studies continue to be conducted, and hopefully we’ll know more in the future.

Birds can also fly into clear windows as a result of seeing and attacking their own reflection. (iii) During nesting season (spring and summer), birds will compete with one another to obtain the best territories for breeding and raising their young. If an ideal nesting site is close to a window that reflects a bird’s image back to it, then an endless battle with a “rival” may ensue. While these bird-versus-reflection skirmishes rarely result in fatal injuries, the bird can easily exhaust itself after exerting a tremendous amount of energy over a long period of time. This depletion of energy can prevent birds from foraging normally, leading to starvation and/or dehydration, and eventually death.

Pictured above is a scarlet tanager (Piranga olivacea), attacking it’s reflection in a car window. Photos provided by Wild Birds Unlimited of Barrie, Ontario. (v)

After most severe window collisions, birds are usually stunned and requires time to regain total awareness of their surroundings. This is usually quite apparent, as stunned birds may be found sitting or lying in a daze on the ground near the window that they flew into. Something that’s less apparent however, is that these birds may have internal injuries that, if left untreated, can be fatal and lead to the animal’s death. Nerve damage, spinal injuries, head trauma, and internal bleeding are among the most common symptoms that we treat in birds that fly into windows. With that in mind, we always recommend bringing stunned birds to our hospital team, even if the bird doesn’t appear to have any external injuries. Internal injuries are extremely hard to diagnose, especially for those with little to no experience rehabilitating wildlife.

At this point you might be asking, “How can I help to prevent birds from running into windows?” Here are some tips to get you started: (iii)

1. Keep birdfeeders and baths at least thirty feet away from glass windows.
2. Place taught netting/screening about three inches out from the window so that the entire window is covered. This will catch incoming birds and bounce them back in the opposite direction, kind of like a slingshot.
3. Install external shutters that can be closed when the window/room is not being used.
4. One-way transparent films may be used to make a window seem opaque to a bird while remaining transparent to humans.
5. Hang windows decorations (sun catchers, dream catchers… etc.) or UV window clings.
6. Replace your windowpanes with bird-safe glass. (iv)

The fall migration is still a couple of months away, but everyone can take steps today to better bird-proof their windows and homes.


Ian Martin, Education Coordinator, 2016

(i) Dr. Daniel Klem. Muhlenberg College. Sheet Glass: An Invisible and Lethal Hazard For Birds.

(ii) Fatal Light Awareness Program Canada

(iii) The Cornell Lab of Ornithology: Why Birds Hit Windows—and How You Can Help Prevent It

(iv) American Bird Conservancy: Effective Window Solutions for Homeowners and Architects

(v) Birds Unlimited of Barrie, Ontario

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