Dinsmore & Silcock, "Lesser Black-Backed Gull at Sutherland Reservoir," from Nebraska Bird Review (June 1993) 61(2).
At 8:45 a.m. CST on 17 December, 1992, we observed a Lesser Blackbacked Gull at Sutherland Reservoir in Lincoln County. The bird was first seen resting on the water in the company of Herring and Ringbilled Gulls. Compared to these species, this bird had a very distinct dark charcoal-gray mantle and upperwings, which were at least a shade darker than the mantle color of a Herring Gull, though definitely not black. When, during a brief period, the bird was compared directly to an adult California Gull, it had a noticeably darker mantle, was slightly larger, and had more obvious dark-brown streaking on the head and nape. In flight, the primary tips were darker than the rest of the flight feathers, and small, white mirrors were visible near the tips of the outer primaries, but were not visible on the underwing, which was pale, with some dark gray on the undersides of the primaries. The underparts, including the breast, belly, and undertail, were white and unmarked. The uppertail was mostly white except for small brown marks on the tips of a couple of the rectrices. The legs were very pale pink rather than yellow. The bill was fairly thin, with a slight gonys, which was not as obvious as those seen on most of the Herring Gulls that were present at the time. The distal half of the bill was yellow, with some dark smudging on the proximal half. The head was mostly white, with some fairly prominent dark-brown streaking, particularly on the crown, nape, and sides of the neck. The iris appeared yellow.
There was some confusion as to the age of the bird. Grant (1986) notes that, for Lesser Black-backed Gulls, " ... a few (as high as 3% in some large samples) have adult plumage but fleshy or greyish legs. These birds usually also have dark on the bill of variable extent, and are then age-able as probable fourth-winters which have yet to acquire fully adult bare parts coloration." Our bird fit this description perfectly. The timing of molt in this species also supports this conclusion, since fourth-winter plumage is acquired in June to November (Grant 1986).
Available at: http://works.bepress.com/stephen_dinsmore/34/