Glass Collisions

How to Keep Birds from Hitting Windows

Vassar Bridge Science Building, N.Y. ©Christine Sheppard
Bird-Strike Prevention: How to Stop Birds From Hitting Windows

Up to 1 billion birds die after hitting windows in the U.S. each year, and almost 50% of these hit home windows. Addressing collisions at home makes a huge difference for birds, and there are many bird window deterrents you can choose to fix your glass.

Feather Friendly Residential Application from Feather Friendly

Installing insect screens can also help prevent window collisions. Photo by Ronstik/Shutterstock

Bird Crash Preventers from Santa Rosa National

Bird-Safe Windows: Start by Identifying Problems

If you're wondering how to keep birds from flying into windows, you might assume that applying bird-friendly solutions to all window is necessary, but that may not be the case: Often, a small number of windows often a majority of the collisions. If you identify and fix only the deadliest windows, you can solve most of the problem by addressing a fraction of your glass.

Start by adding a retrofit on these priority windows:

  • Any window where you have heard a bird hit or where you have found a dead bird.
  • Large windows, especially those that reflect habitat (including sky) or through which you can see sky or greenery on the other side of the building.
  • Windows near bird feeders and bird baths.

 

Then keep paying attention, and take regular walks around the house. If another bird hits a window, add a retrofit. Soon, you will have retrofitted a handful of your windows and saved a lot of birds!


Products That Prevent Collisions

Looking for glass for a new building, or a solution to fix existing windows? Search our comprehensive material database to find the right product.


How to Prevent Birds from Hitting Windows

Thanks to research and experience we now know better how to stop birds from flying into windows. There are several ways to do so: Apply visible patterns to the outside of the glass. (Patterns on the inside are often ineffective because they can be hidden by reflections on the outside of the glass.) We focus on the patterns, but birds focus on the spaces. For the birds, patterns must appear to be solid objects with adjacent spaces that are too small to fly through.

Most birds will avoid glass with vertical or horizontal stripes (or other markings) spaced 2” apart. Stripes should be at least 1/8” wide. A good rule of thumb — you should be able to see the pattern clearly from ten feet away. White stripes tend to perform better because they reflect most light and so are visible against more types of background reflections. A translucent line won't show up as well. Patterns of dots can also work if the diameter of the dots is at least ¼”. Of course, since the spacing is what's important, it doesn't have to be dots or stripes — you can use your imagination.

Also, keep in mind that bigger is better: The wider the lines/dots, the more effective they will be because birds will see them from greater distances. Again, though, the critical issue is the spacing. Until recently, we talked about the ‘2×4 rule' because research by Klem and Roessler showed that vertical lines spaced 4” apart would stop a lot of collisions – and that's still true. However, many small songbirds, and especially hummingbirds, can and will fly through a 4” gap. Two-inch spacing, vertically and horizontally (or at an angle), is enough to dissuade almost all species. For three dimensional solutions like Acopian Birdsavers, mounted away from the glass, 4″ vertical spacing has proved to be effective.

"At Atlanta Audubon, we have retrofitted seven buildings with Collidescape film and have been very happy with the results. The retrofit looks sleek and also makes the windows bird-friendly and allows for public education."

Adam Betuel

Conservation Director
Atlanta Audubon Society

Retrofits can cost a few pennies per window or can be a long-term investment in your home. Patterns and even artwork done on glass with non-toxic tempera paint will last a surprisingly long time, can be easily removed or replaced, and make a nice family or school project, providing a great way to decorate windows for holidays and other special occasions. Other kinds of paint can also be effective, but may be harder to remove. Tape and bird window decals work well if you follow the spacing rules outlined above. In a pinch, you can use sticky notes or even draw on the windows with a bar of soap.

Patterns do not have to be on the glass itself. Three-dimensional solutions in front of the glass are highly effective and can also be unobtrusive. Regular insect screens, for example, eliminate reflections and provide a cushion if a bird does hit a window. If you don't have built-in screens, or your screens only cover part of a window, there are several options, like Easy Up Shades and Bird Screens, which can be installed with suctions cups or hooks. Acopian BirdSavers and Bird Crash Preventers also hang in front of windows and are very effective at bird-window strike prevention.

Visit the home windows section of our Products & Solutions Database to see these and other types of bird-saving products, as well as links to websites where they are available.


Take Action for Birds

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Bird Collision Prevention for Hard-to-Reach Windows

Retrofits should go on the outside of the window whenever possible, but some windows are difficult to access from the outside. So, will it be worth the effort to put something on the inside of the windows?

Only a test can provide the answer. Remembering that bigger is better, especially on the inside of a window. To get started, put a sample of your proposed solution, or even just a sticky note, on the inside of the window. Then look at the window from the outside every hour or two, starting in the early morning.

If you can clearly see your test material, the birds will too, and your “inside” solution (remember proper spacing) may be somewhat effective. However, in many cases, reflections will mask the view during part or all of the day, and you'll need a solution on the outside of your windows. Some window-washing companies are now offering installation of bird-friendly measures as an extra service.


Why Birds Hit Glass

Birds don't understand the concept of glass as an invisible barrier that can also be a mirror. They take what they see literally: Glass appears to be habitat they can fly into, whether that habitat is reflected or visible through glass.

 

Photo of hummingbird

 


Replacement Windows

People often report birds hitting windows after replacing old windows that did not cause many collisions. Several things contribute to this:

  • Many new windows use multi-layered and energy-efficient coatings, both of which make windows more reflective.
  • Screens may be sandwiched between panes of glass and/or may cover only half of a window instead of being full screens on the outside.
  • Individual panes of new glass are often larger than the panes they replaced and lack the muntins and mullions — the “dividers” that used to hold the smaller pieces of glass, while also appearing as obstacles to birds.

There are several strategies for new windows and doors (including sliding glass doors):

  1. Order full external screens, even if the windows do not open.
  2. Choose replacement windows that are not bird friendly and then apply the retrofits discussed above.
  3. Ask for bird-friendly glass.

When ordering replacement windows, it is possible to ask for bird-friendly glass that includes patterns in ultraviolet, ceramic (“frit”), etch, or printed patterns. These options are only just starting to be available for home windows and will likely entail a special order. Look at the new glass options in our Products & Solutions Database for an idea of what might be possible.


Visit our photo gallery to see how a variety of materials and techniques can be used to make buildings safe for birds and great for people.

 

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Bird Collisions on ABC's Blog

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