<lso, male finches have the habit of attacking their mirror images> Here, it's Cardinals, usually the males but often even the hens will put up a fiesty fight with theirselves in window reflections, etc. I had to cut the branches of an oak tree back to keep one youngster from pounding his head into my bedroom window last year. He'd sit on a close branch and dive bomb into the glass so hard I thought either the glass or his head would give way. By cutting the tree back, he had to project himself much farther and ended up fluttering against the window rather than going full-throttle. I'm sure the males see it as a rival, but I have no idea what angers the hens so much. Martha Wells~Flylo Farms~ Texas Zone 8
