TV714 wrote:
The male defending his territory seems like the most likely explanation. The only thing that makes me wonder about this particular bird is that one of our windows is at ground level in our back yard. He was sitting on the ground right at the window where he certainly would have seen his reflection. Yet, he wasn't attacking his reflection, but rather flew up a foot or so and hit the window well above what he was seeing. So, who knows?
Or, it could be a female looking checking her makeup.