Glass, primarily in the form of windows, is a big issue for birds. The problems present in a couple of forms: birds colliding with glass at high speeds, often resulting in injury or death, and birds repeatedly attacking the reflection they see in windows. We’ve been getting a number of inquiries about the latter, but given the pervasive problem with the former — and possibly similar answer to both — I want to cover all things birds-and-glass in this article.

Let’s start with the problem of birds colliding with glass. Although glass windows have been around going back to ancient Roman history, that is a tiny fraction of the millions of years that birds have been evolving, and unfortunately, this “recent” invention is something birds are not equipped to deal with. Go ahead and look up “walks into glass door” on YouTube and you will find endless clips of people, who know there are doors there, still walking right into glass because they don’t see it. Birds don’t even know what glass is, and will often fly right into a glass door or window. This is made even worse by the mirror effect created with glass when it is lighter outside than it is inside. Birds then see the reflection of the sky or nearby trees and shrubs and think that it is someplace they can fly toward, as a continuation of the landscape. 

You may be familiar with the diagnostic “thud” of a bird hitting a window on your house. To put that problem into perspective, consider this: that “thud” is happening more than a billion times annually in the United States. Window strikes peak during spring and fall migration, but averaged out, that’s roughly 32 strikes per second. Compared to other quantified anthropogenic causes of bird mortality, this is second only to the number killed by outdoor cats (both owned and feral), and 999,600,000 more (or roughly 3,000 times more) than the number killed by land-based wind turbines, despite misleading information that is often spread.

We’ve come a long way in developing solutions to the problem, especially in learning what doesn’t work. When I started working at Maine Audubon, there were stickers of kestrel (a bird of prey) silhouettes in the top corners of the large windows along our hallway. During the first spring at our headquarters, I documented 26 strikes of birds hitting those windows. That summer, we applied strips of tape that reflect ultraviolet light to the outside of those windows, and bird strikes dropped to nearly zero. We would still get the occasional strike from birds being chased by predators, like Cooper’s hawks. 

With building renovations earlier this year, we now have “bird safe glass” installed around the entire building and in the two new buildings on campus. The Maine Audubon website has a “Homeowners Guide” that includes a section of do’s and don’ts, as well as a recommended products list with options for various applications, at maineaudubon.org/birdsafe. The most important thing to remember if you are treating your windows is to apply treatments to the outside surface. 

The second, and less lethal, issue is from birds seeing their reflection in windows and thinking that it is a different bird invading their territory. The result is they start attacking the reflection, repeatedly hitting the window as they think they are fighting this new rival. This behavior is usually only seen during the nesting season, and as migration wraps up and many birds are already nesting, we start getting a lot of calls from around the state from people who are dealing with these delirious birds. 

The solution is similar for both issues: break up the reflection or give the birds something to actually see. This can be a bit easier with the aforementioned issue, where we just want birds seeing that there is actually a window there, but with the “intruder” issues, sometimes it takes just a tiny bit of a reflection to set a bird off. This is when something like an outdoor screen is going to be most useful, or dangling strips that may get in the bird’s way. 

While there are more professional solutions, you can also be creative with it. One time, I had to deal with a very aggressive male northern cardinal that kept catching his reflection in my window. I tried hanging a pie plate, which was lightweight and reflective so it moved and flashed in the sunlight, but that wasn’t enough. Eventually, I took a bar of soap and just scribbled all over the window (again, on the outside), and in quick order, the cardinal gave up. After a week or so, I was able to clean the soap off with a hose, and the cardinal’s hormones must have cooled off enough that the problem was solved. 

And if you really want to help birds, please keep your cats indoors. They are non-native surplus-killing apex predators that humans have spread across the globe and are responsible for the extinction of dozens of species. 

Have you got a nature or wildlife question? It doesn’t have to be about birds! Email questions to [email protected] and visitwww.maineaudubon.org to learn more about birding, native plants, and programs and events focusing on Maine wildlife and habitat. Maine Audubon Staff Naturalist Doug Hitchcox and other naturalists lead free bird walks on Thursday mornings starting at 8 am, at Maine Audubon’s Gilsland Farm Audubon Sanctuary in Falmouth.