Why is a bird attacking my window?
Birds like House Finches, Towhees and Mockingbirds will dash repeatedly at their reflections in windows. Such actions are usually because the individual bird, usually a male, mistakenly perceives another bird in the reflection. It is territorial behavior for the bird to fight off the intruder. This behavior, if continued over a period of weeks or even an entire season, can be annoying to people, but is usually not fatal to the bird.
There are two ways to help prevent this behavior...one is to eliminate the reflective qualities of the glass window so it does not act as a mirror, the other is to create a physical barrier between the bird and the window.
A light colored or white material placed against the inside of the glass may help to reduce the reflection enough to stop the attacks. This can be newspaper, a sheet, a white window cleaner or other material. Interior vertical blinds (that are light in color) with the slats half open or closed may help. A dark room or dark drapes will actually increase the reflection and encourage more attacks. You may also apply things to outside of the glass like an opaque window decal, plastic sheet like a grocery bag or soap the window.
If all else fails, you may need to cover the outside of the window with a thin netting to prevent the bird from actually reaching the window. One of the advantages of the netting is that it allows you to still see out the window.