After an initial posting and some reading, I have come to realize that the Downy Woodpecker and the Hairy Woodpecker are quite difficult to distinguish, and this could be either. The large burl on which this bird was moving was 40 to 50 feet up a large tree and difficult to photograph. I have added a third photo, though blurry, in the hope that the profile might offer additional diagnostic information, such as the beak size and shape, that might be useful for identification.