Lee, I can see nothing in these photos that suggest otherwise. It looks to me in all respects like a classic adult Thayer's Gull. We see many like this in the southern interior of British Columbia. The amount of black on the primaries is somewhat reduced but well within the range for a typical Thayer's Gull. Nice photos! - Happy birding, Michael Force, currently aboard NOAA ship McArthur II, about 180 nmi south of Midway,
As no one from the west side of the pond has responded, I'll chime in to say that "no dissenter here". Here in North Carolina, Thayer's is a rarish bird, but I see an adult every few years at Cape Hatteras, and review others' photos for the state records committee. If this were in NC, it's an obvious Thayer's: dark eye -- the first character that "flags" a possible adult Thayer's (or California), legs usually rich pink ("bubble-gum" color as often stated) as opposed to flesh or pale pink of Herring and Iceland; medium-sized bill (usually a tad shorter and thinner than Herring and slightly larger than Iceland forms, but sometimes not really a field mark), pale gray mantle close to Herring, and much reduced black in the primaries when seen in the air, above and below (from below, wing tips are often nearly white). I'm not a classic lariphile that knows and remember the black/white/gray ratio on each flight feathers. But, as this is a first apparent record for Great Britain, I suppose it will need to go thru some scrutiny (hybrid possibility, etc.); but, looks like a good Thayer's to me. Harry LeGrand. Raleigh, NC, USA
And more from Steve Hampton....
Okay, I'll chime in from the West Coast. Looks very good to me. The bill is on the bright side, but the brighter tip, trace of green at the base, and rather small red spot are fine. The dark eye is fine. The extensive head and breast smudging is fine. The hint of cross-barring on the breast is suggestive of Gl-W but is also found on Thayer's, especially in this exact patter with streaks on the head and thicker blotching at the bottom of the breast. See http://johnrakestraw.files.wordpress.com/2009/02/thayers-gull.jpg for a similar example.
The mantle shade seems right-- slightly darker than Herring, although some comparison shots would be nice to a control for camera lighting. The primary pattern is, of course, excellent, with black extending to P5. The pale underside of P10, except for the little black subterm band, looks good for Thayer's as well. Dark pink legs are excellent. Size and shape seem fine. The bird is probably a male based on the bill size. The obvious things to rule out are Gl-W x Herring, which is rather common in southern Alaska and, at least around here in northern Calif in winter, and "Kumlien's". The black in the primary pattern, black to P5 and even a tiny black band on P10, seem good to rule out Kumlien's. Also the shade of mantle gray. Ruling out a petite female Gl-W x Herring might be trickier, as they could potentially mimic the plumage and bare parts. I could see folks commenting on the gonydeal angle and dark mark in the bill as indicative of Gl-W traits... I'd be interested in others' thoughts on how to rule out this possibility. The structure of the bird, with the long primaries, small rounded head, large eye, etc. are all consistent with Thayer's and probably beyond the range of Gl-W x Herring. Steve Hampton