How do I keep birds from flying into my windows?, The Raptor Center at the University of Minnesota

The first question to ask is why birds are hitting the windows. For example, if it is spring or summer and a male cardinal repeatedly knocks himself against the window, it is a very different situation than if a mourning dove barrels head-first into the window. In the first case, it is likely that the cardinal sees his reflection and is defending his territory against the handsome male cardinal reflection that he sees. The solution in this case need only be temporary and should be in place for a matter of weeks or until the breeding season is over. In the second case, it is possible that the mourning dove is trying to escape an avian predator and does not see the glass, but simply sees an escape route.

• While there are many solutions to the problem of window collisions, there isn't one perfect solution. Some of the more effective solutions include -
• Smearing a soapy solution on your windows so that the birds cannot see their reflections.
• Attaching netting or hardware cloth over your windows. This will act like a window trampoline and will keep the birds from killing themselves should they try to fly through your windows.
• Taping a large piece of paper or cardboard to the window. While this is effective, it negates the purpose of having a window.
• Using one of the many specialty products available, including CollidEscape and window film, which are plastic sheets attached to the outside of the window and covering the entire surface. These products decrease the reflective property of the window from the outside, but still allow a good view of the outdoors from the inside.
• Attaching raptor silhouettes, Whispering Windows anti-collision window decals, or Droll Yankees Warning Web decals to your window. These designs work by breaking up the reflections so birds can "see" the glass and avoid striking it. The Warning Web actually has a replica of the white zig-zag stabilimentum - which scientists believe spiders add to their webs as warnings to birds, so that the birds do not fly into and destroy the webs.

According to the United States Fish and Wildlife Service (USFWS), life-sized plastic birds of prey and predator silhouette decals are not effective in keeping irds from striking your windows. Another solution is closing the curtains on the windows, especially if another window can been seen through the problem window. To the birds, this second window looks like a tunnel or escape. If you have plants visible from the outside, the birds might try to escape into the plant cover, or forage in them. Move the indoor plants out of view, or create a barrier so the birds will not think they can reach the plants. Some individuals hang pine cones on fishing line at various heights in front of their windows. Flash tape, such as holographic scare tape for garden plants also works when hung in front of the window. Remember that birds will still try to get through gaps of two inches or more.

Hanging a window feeder on your window will actually decrease collisions, but having bird feeders a few feet from your window will increase collisions. The reason for this is that a feeder placed within five to ten feet of a window allows birds sufficient time to reach a flight speed at which they could kill themselves should they hit the window. It's best to place feeders within two feet of the window or 15 to 35 feet from the house.