Here is a robin. This robin sees himself in the window between himself and my camera. This robin is really mad that this other robin just sits there and stares at him. This robin takes action.
If this robin did not have brain damage before whacking himself repeatedly on my windows, I'm sure he does by now, which is why he continues to go after his reflection day after day, leaving a ribbon of robin gunk that parallels the grape vine conveniently (for him) trained along the top of the sun room window.
And no, he didn't mind me taking pictures of him beating himself up.
I spent several hours cleaning the windows yesterday, and yes, he was back at it this morning.