I have this little feller hopping up and down ourside our front window - either he's courting himself or defending his territory against that Other bird in the window. Crazy, I tell ya. Apparently, he's not hurting himself - he keeps coming back no matter what we do!
ETA - We put up a window decal - he was just at it all the time! From what I know about birds, and cardinals, I'm pretty sure he thinks he's defending his "territory" - but Damn! I don't want him to hurt himself. So far, he hasn't been back since the decal went up. We don't have a cat - and the dogs don't seem to phase him in the least. He's been very determined up until now!! He doesn't seem to be hurting himself - but I don't want to take that chance!