One Flew Over the Cuckoo's Nest

I have a small mirror on a fence post at the top of my driveway, so I can see to the left before I pull out. Today, a little bird saw himself, thought he was another little bird, and went ballistic. He would fight and fuss with the little bird in the mirror, then go away tired, and then come back and fight some more. He pretty much did that all morning. Like many of us, the little bird is his own worst enemy, but I don't know how to tell him that.