This interesting gull was at Pueblo Reservoir on 9 December. Could it be a juv. Slaty-backed Gull? Photos will probably be needed to nail this down, but points in favor of SBGU are brown tail band, extensive paleness in flight feathers, whiter head, darker brown belly, and the bill pattern, dark but blackest at the tip. The digiscoped photo was taken by Cole Wild. Some similar birds, photographed in Japan can be seen at http://www23.tok2.com/home/jgull/040113/slaty2.htm. A candidate imm. SBGU seen in November in Boulder County, CO is a different bird ( http://schmoker.org/BirdPics/PossibleSBGU.html).