Betsy, it seems birds will do that. They think there is a rival as they do not realize it's their own reflection. Someone was saying she's had this happen quite a number of times with her house windows. She said she got a small mirror & hung it near the window & the birds begin attacking the mirror, then gradually you move it a little further away until you can finally get it a goodly distance away hopefully in some tree. At least at that point they are attacking the small mirror & not your car mirrors. Silly birds!