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Minimizing Window Collisions

Large windows reflecting habitat. Photo courtesy U.S. Fish and Wildlife Service


It's estimated that as many as 1 billion birds die each year in the United States due to collisions with windows. Daniel Klem, a biologist at Pennsylvania’s Muhlenberg College, has been studying the problem for three decades and cites window strikes as a major cause of bird fatality. The primary danger stems from reflective glass. Birds see escape routes and possible safety zones mirrored in reflective glass and fly unaware into windows. The speed and force of the impact can cause instant death. Birds that seem stunned or do not die immediately may actually be fatally injured as well - suffering from a brain hemorrhage or other internal bleeding. At the very least, stunned birds are temporarily less responsive and thus highly susceptible to predation. Transparent glass poses a similar threat as birds collide into unseen windows en route to some visible target on the other side.



Feeder Placement

How can this help? Many birds strike windows after being startled off a feeder. Bird feeders placed within three feet of windows can reduce fatal collisions because birds do not have an adequate distance to reach high flight velocity. Placing the feeders more than 30 feet from a window will also reduce window collision risk because, at that distance, birds are more likely to recognize that the reflected image is part of a house and are less likely to fly toward it for safety.

Practicality — HIGH: For homes with feeders, this is an easy and surefire way to reduce deadly window strikes.

Window Shades, Drapes, etc.

How can this help? White or light-colored window shades, blinds, or drapes, when drawn, eliminate much of the mirror effect or transparency of windows.

Practicality — HIGH: Interior window treatments (such as drapery) already exist in many homes. The downside is that they block the view to the outside. Drawing curtains or blinds when leaving for work or vacation is good practice.

Before: Drapes open, window reflects habitat After: Drapes closed, reflection greatly reduced

Window Decals or Items Hung Outside the Window

How can this help? Decals or objects placed on or in front of windows create an interference pattern that reduces the mirror effect of reflective windows and make transparent windows more visible. (For example, see "Wing Chimes" on the Fatal Light Awareness Program link below.)

Practicality — MED: Although decals are easily affixed to windows and are available in a range of styles (it is not necessary to use a hawk silhouette), they must be spaced close to each other to be effective – at most 2 inches apart horizontally, and 4 inches apart vertically. Objects, such as ribbon draped on the exterior side of a window must also be spaced strategically to create density. This density causes too much visual obstruction for many people. Covering just a portion of a window is better than no coverage at all.

Bird Netting

How can this help? Fine mesh netting stretched tightly over an entire window causes birds to "bounce" away before crashing into window glass and does not obstruct the view.

Practicality — MED: Works well but requires some do-it-yourself agility; poses entanglement risk if not properly installed. Netting must be taut and at the appropriate distance from the window. Adhere to instructions available with product or on the internet.

Window tilted - ground is reflected

Tilted Glass

How can this help? Tilting the glass in a window causes the ground to be reflected rather than possible shelter and escape routes for fleeing birds.

Practicality – MED: Not a foolproof solution but an easy way to address the problem during the construction or remodeling phase of a building. With supporting research, this practice might be commonplace in the future.

Fritted Glass

How can this help? Fritted glass has granules fused onto it to create a frost-like pattern that reduces its reflectivity and transparency.

Practicality — LOW: Currently being tested on a college campus, it holds some promise for widespread use in commercial and residential applications. May be perceived as esthetically unappealing by the general public and obstructs open view to the outside.

Window Films

How can this help? An opaque sheet of plastic attached to windows gives them a solid appearance.

Practicality — LOW: Films currently available to the general public severely limit visibility.

Bug Screen

How can this help? Bug screens or summer screens on the outside of exterior glass kept in place year-round will cut down on reflectivity and transparency while acting as barrier to birds and insect during warmer months.

Practicality – HIGH: In newer construction, double paned windows can be shielded by screens. In older homes with storm windows, screens would need to be switched with exterior glass.


Further Resources:

FLAP: Fatal Light Awareness Program
Extensive information and resources on bird collision issues

Philadelphia Inquirer Magazine, May 10, 2003
Fatal Reflections
by Maryalice Yakutchik
Feature article on Daniel Klem’s research on bird-window collisions