I have the same problem with an especially stubborn Eastern Bluebird. If she is back this year, it will be the third year in a row. I think she wants to scare away the other female she sees in the reflection of the window, but this goofy chick (pun intended) actually flies around the house, scaring away ALL those other pesky other females! Last year she was stalking my husband. EVERY room he was in, she found the window and dive bombed it several times. The poor little male is just hovering, trying to get her attention. It's comical to watch, but I, too am afraid she will hurt herself.
