I believe this is a male shiny cowbird. We saw quite a few today. I was commenting to Marc that we were seeing plenty of individual male Red-winged blackbirds, but not the large flocks that we saw in the winter. He commented that was because they were breeding.
I think that's a good explanation for this bird. The female blackbirds are off tending their nests, and the female cowbirds are laying their eggs in the blackbird's nests, for the blackbirds to raise!