I think it's a robin. We're actually feeling kind of flattered to have had our yard chosen for this event! My son thinks the birdhouse he made with his grandfather is what attracted it.
It took me by surprise when I first found eyes staring down a beak at me. I noticed the nest when I was clipping some long branches, but I saw the bird for the first time when I was ducking beneath the tree to move the hose. I talk to it every day so it will hopefully get the idea that I'm freindly. My FIL had a thing going with a bird one summer-it dive-bombed his head almost every time he went in the back yard.