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17 hours ago, Aidan B said:

It looks like Thayer's to me, Iceland should be whiter, almost like a Glaucous Gull

Iceland Gull shows a full spectrum from clean white primaries (glaucoides), to gray primaries (Kumlien’s), to black (Thayer’s).

It is related to the geographic area where they breed, with broad intergrade zones I believe, so there is everything from clean white primaries to black primaries and everything in between.

Overall this bird looks paler than I’m used to with second winter Thayer’s, but not drastically so. I don’t know enough to say for sure whether it’s Thayer’s or Kumlien’s (or intermediate), so that’s why I’m suggesting Thayer’s/Kumlien’s.

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First off, it is important to note that this is a second-cycle bird, which makes assessment of whether it's referable to kumleini or thayeri much more problematic. As AH noted, even kumleini is quite variable in overall darkness and combining that with the bird's age make assessing which form to which to assign any single individual solely by plumage something of a Sisphyean task. The bird's strongly angled forehead and large size (relative to the Herrings around it) suggest that it's a Thayer's Gull, as that form is, on average, larger and has a more-angled head than kumleini  Unfortunately, head shape is also a feature that differs between the sexes of both forms. However, the bird's whiteness on the wings might suggest kumleini. Thus, I agree with AH's suggestion of not assigning the bird to a particular subspecies.

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