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Birds of many types have been killed by flying into glass windows and doors. According to the Audubon Society, collisions with glass may be a major source of avian mortality that's widely overlooked.

Although there are several variables which account for bird strikes, the primary cause is reflection. Birds become confused or startled and rush to cover or open sky; unfortunately they often mistake a reflection for the real thing.

In cities the biggest kills typically occur at night during spring and fall migrations, when building lights appeared to lure birds into deadly collisions. Light-dimming campaigns, such as those led by the Toronto-based Fatal Light Awareness Program, have helped reduce the problem.

Here are 9 ways to reduce bird strike occurrences in homes and small buildings:

1. Observation

Bird strikes often follow a pattern – the same windows on a house or building may be repeatedly struck, while others are never struck. Observation and attention to bird attractions such as water, food and cover, will help identify the small percentage of glass area in your home which causes the most problem.

2. Block 'through-house' line of sight to the outdoors

Are any windows in your home oriented such that, from the outside, there is a clear view through the house and to another window looking to the outside? A bird may see this as a flight path. This can be changed simply by putting up a shade on the one window, or closing a door or similar obstruction which breaks the open view.

In our home, for example, we noticed that bird window collisions seemed to occur most often in a corner window on the second floor. While on the roof one day cleaning the eavestroughs, I stood outside the window and observed it from a bird’s point of view. Sure enough, a path of vision to a window on the opposite side gave the impression you could fly right through. This was corrected by lowering the blind on the opposing window, and leaving the slats open for light. We have not seen any window strikes since.

3. Reduce window reflection

Birds often strike windows because they see a reflection of clouds, sky or trees which gives the mistaken impression that they are flying into open air. Put a screen or a shade cloth over the window which is nearest to bird activity. A shade cloth, available at hardware stores, is a plastic mesh that allows you to see through, yet keeps the windows from having reflections. If you have blinds, turn them so they are slightly closed, this will reduce reflection. White shears also work to reduce reflection while being able to see through.

4. CollidEscape and window decals

CollidEscape is a transparent film which adheres to the exterior surface of a window, and allows ample light to pass through to the interior, while reducing the window’s exterior reflectivity and transparency. This material is primarily used for commercial and retail advertising on glass. The cost is approximately $4.00 US per square foot.

Many different window decals are on the market for applying to your window for bird strike prevention. These commonly come in the outline form of a hawk silhouette or spider web. While these may be effective, it is difficult to judge if they make a difference in reducing strikes. Birds may not be deterred by stationery objects such as decals.

5. Place a hawk silhouette on your window

Most smaller birds will avoid the company of hawks, especially the sharp-shinned hawk which flies low into cover, often near feeders, and preys on small birds. A hawk simulation can be placed on your window or glass door to discourage birds from flying in this direction. The key is to hang this on the outside of the window, using a suction cup with a bit of clear fishing line to hang the silhouette so it swings in the wind.

You can make a life-sized hawk silhouette by copying the image here, and scaling it up to an 11” wingspan. Trace the image onto a piece of corplast (available in building supply stores) or similar black plastic, and cut it out with a razor knife. Use fish line and suction cup to suspend from the outside of the window.

Hanging a plastic owl is not effective over time, as the figure never moves and birds quickly learn to ignore it.

6. Tack up a temporary cover

Sometimes a more aggressive behavior occurs, typically in the breeding season, where a bird repeatedly ‘attacks’ a window. Seeing its own refection as another bird, it’s trying to drive it away, as songbirds are competitive during breeding times. A cloth, piece of netting or solid material can be placed on the outside of the window for a few days to break the bird of its habit. Or you can install indoor-outdoor blinds on the outside of the window.

We have a robin that appears in the spring and repeatedly attacks the window of our car in the carport. The bird is seeing its reflection in the window, and perceives this as a territorial intruder. Hanging a small towel over the window stopped the behavior, and we only needed to do this for a few weeks during the spring.

7. Place sun ornament, crystal or other objects in your window

Sun ornaments, crystals, strips of cloth and other objects in the window will help birds know they can’t fly through. Avoid hanging plants in front of windows which are in areas of high bird activity – this can further confuse the bird which may fly towards the plant looking for shelter. Double-pane windows have enhanced reflection and are harder for a bird to see through.

8. Locate prey and food attractants away from windows

During spring and summer, bright flowers on the inside windowsill can attract hummingbirds. Hummingbirds usually approach quickly, then hover, before putting their beak into the flower. If the flower is right against the window, the bird will likely stop in time. But if the flower is set back 6” – 12” from the window, an accidental strike may occur.

In our home, we used to keep a fish tank on a counter near the front window. Over time we realized that in the evening an owl would perch outside and occasionally strike the widow, apparently attracted by the fish, since the tank was illuminated by the interior room light. Moving the fish tank solved the problem. If you have a hamster cage, fish tank, or similar attractant, you may consider moving it if you have noticed repeated bird strikes against a nearby window.

9. Locate bird feeders adjacent to, or further away from windows

Bird feeders should be positioned either further back in the yard or up close within 2 or 3 feet of a window. By placing the feeder up close, birds come in at a slower speed; they’re less likely to get hurt during escape because window strikes occur at slower speed. By placing the feeder further out (10 feet or more), the bird has more room to maneuver. Cats are usually wise to the presence of birds around feeders, and the bird needs space to escape in any direction. Locating the feeder in the 3’ – 10’ zone from the window may result in more window strikes.

Window mounted bird feeders do not encourage bird window strikes.

If you find a bird stunned by a window collision:
Often when a bird collides with a window, it is just stunned and will be flying again within an hour, after regaining its senses. With gloved hands, carefully pick up the bird and place it in a safe area away from cats and other predators. In cool weather, place the bird in a well-ventilated box in a warm area to recover. Avoid handling the bird and the box as much as possible. Never handle birds or any other wild animal with your bare hands.