Window kills and how to prevent them

From an article originally written for our web site by Christine Hanrahan

Long ribbons added to the outside of a building in downtown Ottawa during FalconWatch

Long ribbons added to the outside of a building in downtown Ottawa during FalconWatch

Many of us have had the sad experience of finding a dead or injured bird that has flown into one of our windows. If the bird is lucky, it has only been stunned and will recover, but in many cases the impact is too severe.

Windows kill birds in the day and night, throughout the year, and under most weather conditions. The annual mortality resulting from window collisions in the United States is estimated at 100 million birds. Bird kills can be reduced using the following techniques.

Why do birds fly into windows?

Windows reflect an unbroken image of trees, shrubs, and sky. Birds can’t distinguish between the reflection and the real thing, so they fly straight at the window expecting to continue through. Large windows are the worst culprit, but even those with small panes can be lethal.

How you can help prevent the problem

  • Feeders and bird baths can be a hazard if they are near large windows. Make sure startled birds can’t hurt themselves by putting these attractants less than half a metre from the window so that the birds won’t be able to build up enough momentum to sustain serious injury if they hit the glass; or place them far enough way, such as at the end of the garden, near shrubs into which they can escape.
  • Glass panes must be completely covered if collisions are to be eliminated. Screens help. You can also keep your curtains or blinds drawn to cut down on the illusion that your window is a continuation of the outside.
  • Single objects – falcon silhouettes, owl decals and large eye patterns – DO NOT reduce strike rates. Glass must be uniformly covered with objects or patterns 5 to 10 cm apart to break up the area into something birds will recognize as a solid surface.
  • Cut shapes, such as balls, bells, stars, birds, out of aluminum pie plates, hang by fishing line and affix by suction cups to the outside of your window.
  • Fine netting across windows can also help to break up the reflective surface. The Fatal Light Awareness Program (F.L.A.P) suggests leaving a space between the glass and netting so that it will act as a trampoline if a bird hits.
  • Used CDs are excellent for breaking up reflection. String them on fishing line, ribbon, or raffia and hang two or three in a large picture window. You can glue two together, shiny side out, to create a silvery surface on both sides. These recycled CDs look very much like suncatchers or other attractive window ornaments. Some people even paint flowers or birds on one side, or cover one side with stickers of flowers, butterflies, or birds.
  • FeatherGuard developed by Stiles Thomas (2001) is another innovative solution that he claims works well. FeatherGuard is simply a fishing line strung with feathers every 7 inches and affixed vertically to the window by nails top and bottom, with only enough slack to allow the line to move in the breeze. To tie the feather to the fishing line, drill a hole in the feather shaft and thread with the fishing line, tie a knot to secure it, repeat every 7 inches. Feathers about 6-8 inches long work best and you can buy bags of feathers from craft stores or dollar stores.
  • Try hanging strips of tin foil, long coloured ribbons, strips of cloth, or small bells outside the window, to keep the birds away from the glass.
  • Spider web decals (available under the name Warning Web) have been reported as working well – you’ll need a number if you have a big window.
  • Think like a bird! Take a good look at all your windows from the outside in bright daylight. You may not be able to see things on the inside. Try to find the right combination of plants, blinds, screens, etc. that will be visible to birds and will give them the clues they need to avoid your windows.
  • Finally…. Talk to your family, friends and your neighbours. Spread the word about this issue Many people may be unaware of the problem or feel unable to do anything. To be informed is to be empowered.


One of the best sources of information about this issue is the Fatal Light Awareness Program (F.L.A.P.) in Toronto. They run an excellent website at and produce a biannual newsletter Touching Down. Their primary focus is working to protect migratory birds from crashing into urban buildings, but they offer advice and information for everyone concerned with this problem. They have done a remarkable job in getting a number of Toronto’s biggest office towers to turn off or turn down their lights during spring and fall migrations, the periods when most bird and building collisions occur in the urban setting.

Making your windows safe for birds, Cornell Lab of Ornithology

Window collisions, Cornell Lab of Ornithology

15 products that prevent window strikes

Sources for this material

  • Daniel Kelm Jr. Collisions between birds and windows: mortality and prevention. Journal of Field Ornithology, 61(1), Winter 1990.
  • Patricia Adams. Birds flying into windows – what to do. Michigan Audubon Society.
  • Thoma Stiles. FeatherGuard: an innovative solution to the vexing problem of window-killed birds. Bird Watchers Digest, Sept/Oct. 2001.