Why collisions happen

Collisions occur for two main reasons:

Reflections

Birds see habitat and open sky reflected on our windows. Almost any glass can act like a perfect mirror under certain lighting conditions. Deceived by the reflection, they crash into the solid glass trying to reach what they see. Photo: North Mymms … — Birds see habitat and open sky reflected on our windows. Almost any glass can act like a perfect mirror under certain lighting conditions. Deceived by the reflection, they crash into the solid glass trying to reach what they see. Photo: North Mymms News, CC BY-NC-SA 4.0.

The Results

When birds strike windows they suffer head trauma, usually concussions, often severe enough to result in blood seeping out of their eyes and bill. Other times there is no visible evidence.

See-through

Wherever birds can see habitat or sky through glass, such as windows opposite one another (above), glass walkways, sunrooms, glass enclosed porches, etc., the result can be lethal. This is one time where closing blinds can be very effective in preve… — Wherever birds can see habitat or sky through glass, such as windows opposite one another (above), glass walkways, sunrooms, glass enclosed porches, etc., the result can be lethal. This is one time where closing blinds can be very effective in preventing collisions. Photo: Peter Saenger.

What you can do

There are easy, economical ways to help birds see your windows.

Hanging cords, strings, or ribbons in front (outside) of your windows on 4" centers can be effective and unobtrusive. These are simple and easy to do yourself.
Thin tape applied to the outside of the windows on 4” centers also works.
UV marker or tempera paint can be a temporary solution.

Image: Bird window Collision Working Group (BCWG), a collaboration between: The Acopian Center for Ornithology, Muhlenberg College, Lehigh Valley Audubon Society , Wyncote Audubon Society , and Audubon Pennsylvania.

Regardless of the method you use, it is important that you follow the 2”X4” rule. According to the 2”X4” rule uniformly cover the outside of your windows with a contrasting pattern of shapes spaced no farther apart than 2 inches vertically and 4 inches horizontally. To protect small birds like warblers and hummingbirds, 2”X2” spacing would be better.

Hanging cords

Acopian BirdSavers (birdsavers.com) are easy to install, long lasting, and highly effective. They are also simple and easy to make yourself. The BirdSavers website gives directions to build your own, or order them from Acopian BirdSavers. Approximately $2.98 materials cost* or .25 cents per Sq. Ft. if you build your own or $2.50 a sq. ft. if you buy them premade.

Tape

Feather Friendly (featherfriendly.com) bird tape consists of adhesive markers applied to the exterior surface of glass to provide visibility to birds and barely noticeable to people. After applying using the 2”X4” rule the dotted pattern is visible to birds and will substantially reduce bird collisions.

Temporary measures

Tempera paint is long-lasting, even in rain, and non-toxic that can alter the transparency of windows. Use a brush or sponge to apply it to the windows. Because it is relatively inexpensive and easy to remove it can be used to collision proof windows in situations where more permanent or more expensive solutions may not be viable. Be sure to follow the 2”X4” rule.

Other temporary solutions are UV decals or applying UV marker or poster paint to the outside of windows. Ultraviolet light is visible to birds but not humans. The reflectivity of the UV degrades rather quickly. Using enough decals to follow the 2”X4” rule can be expensive.

What doesn’t work

It is ineffective to use hawk silhouettes (unless multiple silhouettes are applied in a dense pattern), single window decals, or any visual markers that do not follow the 2”X4” rule.