I went over to Schoolhouse pond at lunchtime today.  Scoping from near the road I found a 1st winter Lesser Black-backed Gull and then a 1st winter white-winged gull, (which I took to be Kumlien's) both fairly close in. I then made my way over to another part of the pond and bumped into Jim Stasz and Fred Shaffer.  They had located the white-winged gull, which had moved to the back of the pond, and there was some discussion on whether its structure, in particular the bill, was not right for Kumlien's and that it might be Thayer's.  After a while the bird flew again to the front of the pond and I got some pictures (not great I am afraid):
  
http://harrisbirds.com/Kumliens%20Dec%20MD.htm
   
  It is quite long-billed for Kumlien's but it looks to fit some of the larger billed individuals in the new Howell/Dunn guide (eg 35A18 and 35A15).  In general the plumage seems fine for Kumlien's. I didn't get flight shots but the primaries were pale with a thin brown line along the web and that tail was rather solidly pale brown.  The primaries would seem to be extreme for Thayer's.  Any feedback would be much appreciated.
   
  Regards
   
  Clive Harris
  Cabin John, MD