This spring, we have been battling a bluebird, or rather, he has been fighting every reflective surface around our yard in an attempt to defeat the enemy he sees in the glass. His favorite opponent is my husband's shiny new company truck. It has large side mirrors and a wide back glass that displays many other bluebirds to attack. He hops along the bed cover, flying into the window as he pecks at his reflection, splattering droppings the whole way. He also finds a nemesis in the large side-view mirrors, and even when we fold them towards the window, he slips between the mirror and the window and attacks the bird he sees.
He attacks any other vehicle in the yard, too, and pecks at the windows in the house that are in his line of sight from the birdhouse. He even flew on top of the house and attacked the skylights in the roof; we heard pecking on the glass and went into the room to find an angry bluebird furiously attacking the bird he saw.
Because the owners of the shiny new truck aren't happy about its adornment with bluebird droppings, and my husband, Scott, wasn't happy about washing the truck almost daily, he moved it out of the line of sight of the birdhouse. Bluebirds are territorial; and apparently, the territory only extends to areas the bird sees from the house. When we installed our houses, we put the houses out of sight of each other, never imagining that vehicles and windows in our house would become targets. After Scott moved his truck out of line of sight from the bluebird house, the bird stopped attacking his truck and moved to other targets.
One afternoon, while the male bluebird was busy attacking Scott's truck, a female bird, presumably his mate, flew around him and perched on the vehicle as he pecked away. They were engaged in some animated conversation, involving loud squawks and jumping about. I do not speak bluebird, but this is what I think the female, surely a more levelheaded bird, was saying to her mate: “You fool, can't you see it's your reflection you're attacking? Don't you think that if it was a REAL bird it would have pecked back by now? I'm at home trying to take care of my nest and to raise babies, and here you are out fighting. How about staying home and guarding the nest from real invaders!”
Unfortunately, it seems that the bluebirds abandoned their nest without raising any young. Perhaps the male was too busy protecting his nest from imaginary invaders to be able to protect the nest from real invaders, or perhaps he was too tired from his attacks to help feed them. Maybe there was another problem. We have had the houses in that spot several years without any problems, and I hope the next birds to inhabit it will be able to differentiate real and imaginary invaders.