Certain species of birds, typically robins, cardinals, blue jays and house finches become territorial early in the nesting season. These birds see their reflection in windows and mirrors and think it’s a competing bird and will try to drive it away by attacking. If a bird persists at a particular window you can attempt to prevent continued attacks by partially covering the reflective surface with a sheet or tarp for 2-3 days to break the behavior. You could also try mylar strips (reflective streamers that can be found at a store like The Andersons). Screening or soaping the outside of the window can also be very effective.
Additional Information:
- Wild Birds Unlimited – What can I do about a bird attacking my window?
- Wild Birds Unlimited – Preventing window strikes
- Bird Control Products