We see these around the neighborhood every once in a while. Usually hear them first. The Downy Woodpecker is the smallest woodpecker in North America, nests in tree cavities, flies in a kind of swooping up then coasting down pattern, and forages for insects by digging into tree trunks with their bills. S. thinks they look a bit like a checkerboard. For more info. see here.
UPDATE: Spring 2010.