The Blue Bird of crappiness!

Last year, I put up a blue bird box on my back fence. A nesting pair of Eastern blue birds promptly moved in and subsequently reared two clutches of eggs, then moved out. Well, this year, as Spring approaches, a pair has once again started bringing nesting materials to the box. However, I think this is a different pair. Well, at least one of them,probably the male, has taken up the habit of perching atop the large, driver's side, side-view mirror on my van. He leans way over to confront the other blue bird in the mirror with what I'm sure are threat verbalizations. When that doesn't work, he turns back around and craps on his rival in the mirror. Sarah cleaned it off this morning, but I'm sure he'll be right back at it. It figures.