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Bird-Window Collision Reduction: Tips and Techniques for Residents

Why Birds Collide with Windows

Northern Goshawk that collided with a residential window
(Photo: FLAP)

Birds cannot see glass. birds see trees and shrubs reflected in the windows of our homes and fly towards them. They also perceive a clear passage through the transparent glass found on structures like greenhouses, solariums and atriums, or through windows designed to meet at the corners or that run parallel to each other. Bird fatalities from window collisions occur frequently in residential areas because of these characteristics.

You Can Help Make Windows Safe for Birds

You can help reduce, and in some cases eliminate, bird-window collisions at your home with easy and inexpensive window treatments. The key is to provide birds with the visual cues they need to alert them to the presence of glass.

Common Myths about Bird Deterrents

Before we introduce the techniques that DO help reduce bird-window collisions, it might be helpful to introduce, and do away with, the myths surrounding bird deterrents that DON’T work.

  • Hawk Silhouettes: Single window decals in the shape of a hawk silhouette do not frighten birds. The shape of a window decal is unimportant in bird-window collision prevention. It’s the use of multiple window decals, of any shape, that helps make windows visible to birds.
  • Single Window Decals: The use of single decals (including WindowAlert), affixed to a window will not deter birds. One decal covers only one small portion of a window. Unless the bird is headed for that spot it will not be alerted to danger. The use of multiple decals lessens the areas of exposed glass and helps make windows visible to birds.
  • Noise Deterrents: Common noise deterrents include high-frequency ultrasound, noise cannons and the recorded distress calls of various species of birds. In urban settings, these devices attempt to deter birds where colonies of resident species, like pigeons, are situated in public areas. Noise deterrents are ineffective at preventing birds from colliding with windows.
  • Plastic Owls: birds quickly learn that a motionless plastic owl is not a threat. This type of deterrent is ineffective at preventing bird-window collisions.
  • Magnetic Fields: Some bird deterrents emit a magnetic field which theoretically disrupts a bird’s geomagnetic orientation and encourages them to avoid the area. Magnetic fields are not effective at protecting birds from window collisions.

A Rule-of-Thumb to Follow for Visual Markers on Windows

Ornithological research strongly supports that by correctly following the instructions below, bird-window collisions can be greatly reduced, and in some cases eliminated.

  • Uniformly cover windows with a pattern of any shape so that the pattern elements are separated by 10cm (4 in) if applied in vertical columns or by 5 cm (2 in) if applied in horizontal rows.
  • Pattern elements can vary in width from 0.32 cm (1/8 of an inch) or greater.
  • Pattern elements should contrast as much as possible with the clear or reflective window pane to be effectively visible to birds.
  • At see-through sites where clear panes are located one behind the other (e.g., greenhouses, solariums, glass walkways, corner windows) or where clear panes allow views of interior plants, uniform patterns can be applied to either the inner or outer window surface. Please note, applications to the outer window surface provide the best results.
  • Uniform patterns on reflective windows must be applied to the outside surface in order to best disrupt the illusion of facing habitat and sky.

Visit Dr. Daniel Klem, Jr.’s website to learn more.

This beautiful image of a barn swallow illustrates how birds can navigate through tight spaces. This is why the rule-of-thumb is so important.

Strategies for Glass:

Create Visual Markers on Windows

Whichever technique you choose, we recommend that you apply it to the outside of your window for the best results.


Apply window decals to the outside of your windows in a dense pattern that meets the requirements of the rule-of-thumb above.

Window decals can be any shape – birds, flowers, geometric patterns, etc. - as long as they are used in a dense pattern that minimizes the areas of exposed glass. It's not the shape of the decal that deters birds from hitting windows; it's the visual cue provided by a dense pattern of multiple decals that alerts birds to the presence of glass.

Important Note: The illustration (on the left, above) of an effective application of window decals may seem exaggerated, but it is actually the ideal to aim for. Completely covering your window is not always practical or desirable for a variety of reasons, but try and cover as much of your window as you can to alert the birds to the presence of glass.

Visual markers on windows are the most effective collision reduction strategy when properly applied and potentially remove the need for using any other techniques.

Retrofit Technology For Your Home

Markham window film application.
(Photo: FLAP)


Feather Friendly® Technologies in association with the Convenience Group provide window film technologies designed to reduce bird collisions. The solution consists of the application of various patterns of visual markers of a specific size, colour, and spacing to the exterior glass surface to provide the necessary visual signals for birds to avoid impact. The solution provides in excess of 98% clear viewing by building occupants and is ideal for new construction and retrofits on existing buildings. A do it yourself residential kit is available.

In 2009, FLAP partnered with the City of Markham to test a Feather Friendly Technologies patterned film on the windows of a City of Markham building, 8100 Warden Avenue (see image on the left). The analysis of FLAP's collision records at this site demonstrated an annual attrition rate of over 100 birds. Following the application of this test film, site visits concluded over a 97% reduction in bird collisions.

FLAP participated in additional field research in 2012 at both Consilium Place and Yonge Corporate Centre in Toronto that involved a new generation of Feather Friendly Technologies window film (see image on the left). As a result, both locations also experienced dramatic reductions in bird collisions.

For more information, visit: Feather Friendly®

New generation of window film.
(Photo: FLAP)
Close-up of CollidEscape.


Protect birds with CollidEscape, a densely-perforated window film with the best results for reducing collisions. CollidEscape is used on many existing buildings for the purposes of advertising or security.

From the outside, CollidEscape looks opaque and eliminates window reflection and transparency. This protects birds from collisions. From the inside, CollidEscape looks like a window screen. This preserves your view and the flow of natural light into your home.

This image captures the mid-way installation of CollidEscape at the Toronto Zoo.
(Photo: FLAP)

In 2001, the Toronto Zoo applied a similar product on an expanse of glass known to kill birds at their facility. They reported complete success in eliminating bird-window collisions at this location.

CollidEscape and FLAP have a long-standing partnership in their commitment to prevent birds from colliding with windows. Visit CollidEscape for FAQ's, photos of CollidEscape installations, and purchase information.

Important Note: CollidEscape is better suited as a daytime collision prevention technique. At night, CollidEscape becomes see-through from the exterior.

Photo: FLAP


Decorate your windows with a window film that mimics the beauty of etched glass or sandblasting. Keep the rule-of-thumb in mind when choosing your pattern; exposed areas of glass should be no more than 5 cm (2 in) apart horizontally or 10 cm (4 in) apart vertically to have the best effect at reducing window collisions.

The image (on the left) of the white tree silhouettes is an example of the type of window film application that you can have designed through your local, custom film company. There are similar types of window film designs that can be purchased at many hardware stores and glass/mirror companies for exterior use applications.


Install window screening or dense netting, stretched tightly across the outside surface of your windows. Stretching these materials tightly provides a cushion effect for birds if they fly at the window, and also protects them from getting tangled. In some cases, birds see the netting or screen and avoid impact entirely.

Leave a minimum space of 5 cm (2 in) between the window and the netting or screen. This space softens the impact so that if birds do collide with the material they won't hit the glass.

Visit for examples of window screening products that protect birds from harmful collisions.

Visit for examples of exterior window netting with a dense mesh.

Image: FLAP


Hang strips of ribbon, string or other material 10 cm (4 in) apart, across the full width of the outside of your windows. The vertical lines create visual noise for birds and alert them to the presence of glass. This strategy is also suitable for certain commercial settings, i.e. industrial buildings.

For a string system you can purchse, visit Acopian Bird Savers at:


Whitewashing is an inexpensive, temporary alternative that is highly effective at reducing bird collisions with windows. Whitewash is easy to apply at the beginning of each migration season and easy to wash off at the end of each season.

The Toronto Zoo initially whitewashed a dangerous expanse of glass on their property where birds frequently collided. Although this technique is less appealing aesthetically, the zoo reported 100% success in preventing collisions at this site.

Image: FLAP


Position your bird feeders, birdbaths and other attractants half a meter (1.5 feet) or less from your windows. From this short distance, birds cannot build up enough momentum to injure themselves should they hit your window. This may seem counter-intuitive, but the closer the bird feeder to your window, the better for the birds and your viewing!

Image: FLAP


If you can see your houseplants from the outside of your home, then so can the birds. birds perceive your houseplants as a possible perch or refuge. Moving your houseplants back from your windows lessens this attraction.

Image: FLAP


Close curtains and blinds to reduce the dangerous illusion of clear passage through windows, especially those that meet at corners, or where windows are situated in line with one another at the front and back of your home.

Exterior window awnings can also help mute window reflection and help protect birds from the illusion of a clear passage.

Photo: FLAP


Create some visual noise for birds with lightweight items from around your home that won't damage your windows. You can hang almost anything on the outside of your windows as long as whatever you use is applied according to the rule-of-thumb (above). Here are a few ideas:

  • Used CDs
  • Pine cones
  • Sun catchers
  • Laminated pictures or photographs
  • Seasonal decorations

Keep in mind the example on the left doesn’t meet the rule of thumb. Increasing the number of streamers and moving the bird feeder a half meter or less from the window will improve its effectiveness in reducing bird collisions

Get Involved and Help Save birds!

  • Email any ideas, tips or techniques for reducing bird-window collisions that have worked for you to
  • Raise awareness of the bird-window collision problem at your workplace. Encourage building managers to consult and implement Toronto's Bird-Friendly Building Guidelines.
  • Make a donation to FLAP and help support our Bird Rescue. As a donor, you will receive two issues per year of our newsletter, Touching Down, and periodic bulletins about rescue, recovery and rehabilitation efforts in our work with migratory birds.

For information on emerging technologies click here.

If you have any questions or comments, or if you need some assistance with a unique bird-window collision problem that you did not find on our webpage, please call us at (416) 366-3527 or email us at and we will be happy to help you.