"Kumlien's" / Thayer's Gull intergrade, juvenal / first basic plumage
The following photos are all thought to show the same individual; all but the first two definitely do. According to Dr. Jiguet, the narrow tail band, together with the barred scapulars, do not fit what is known from Thayer's Gull on its West Coast wintering sites, and would be interpreted as a sign of intergradation with Iceland Gull (Larus glaucoides), so that this bird looks like the darker extremes of "Kumlien's Gull" (variously treated as a Thayer's x Iceland hybrid or a race of the Iceland Gull). Similar birds seen in Iceland are considered dark "Kumlien's" by European gull experts. In the U.S., on the other hand, this bird would probably be considered nearer the Thayer's end of the spectrum because of the dark patterns in the outer primaries and the hint of a dark secondary bar.
At any rate, the scapulars on this bird are unlike juvenal Thayer's, but are typical of either juvenal (first-generation) or second-generation Iceland scapulars. Thayer's should still have plain first-generation scapulars in December (see above). Also note that the tertials are mostly white with dark barring, unlike the typical pattern for Thayer's demonstrated in the photos above.
