This may well be the last batch of images that I can feature on this interesting bird. It has more than a passing resemblance to a first-cycle Thayer's but I and several other observers have found the overall size (about the same as average American Herring Gull) and the rather ragged look to the scapulars a little off putting. Also, there's been a constant question mark over the pattern of the outer primaries on the spread wing which have always appeared less strikingly 'two-toned' than most first-cycle Thayer's that I've seen. Unfortunately, I don't have any shots that show the spread wings well.
This bird may well elude identification and appears to have moved on. It wasn't in the gull roost this evening (03/02/09) and may have been last recorded by Tom Pirro on Feb 27th which also happened to be the last evening that the Slaty-backed Gull was recorded! Here's a link to Tom's blog entry.