This odd gull was at Pueblo Reservoir on 9 Dec 2006 near Pueblo, Colorado, in the southwest USA. Tentative ID was a small Great Black-backed Gull (L. marinus), a rare but regular stragger from the northeast USA. What else could it be? Possibly the same bird was photographed on 11 Nov 2006 at the same location by Brandon Percival (see photo below).
Compare my written description (below) to Hans Larsson's drawing of a 1st winter-summer Heuglin's Gull (L. heuglini), a plumage that occurs beginning in December according to Olsen and Larsson, 2003 (Gulls of North America, Europe and Asia).
There is much confusion about the species status of this life form. PJ Grant (Gulls 1986) treats it as a subspecies of Herring Gull (L. argentatus). Shirihai & Christie (Birder's Guide to European and Middle Eastern Birds, 1996) call it Siberian Gull (L. heuglini heuglini). Olsen treats it as a full species but indicates that in 2003 official status was a subspecies of Lesser Black-backed Gull (L. fuscus).
