It's like the Hitchcock movie, "The Birds"

At least all week long, a male Cardinal has been banging himself up against the windows in my office. At first I thought he was like many others, who have flown into the glass, not realizing it was glass. As the days progressed though, I thought he was trying to get in my office. Nothing deterred him, me waving my arms and yelling or the dogs fiercely barking and jumping at the windows. Sometimes he sits right on the sill and seems to look into the window at the dogs.
Turns out Cardinals are very territorial. He's not seeing me or the dogs, he is fixated on his own reflection and he's trying to fight himself.
I've resisted putting the screens up that came with the windows as they are heavy duty and will compromise my view of the beautiful Ozark Mountains here, but we're going to have to do it this weekend...at least until we can afford the shades I want and then I can just draw the shades part way during mating season.