presumed Thayer's Gull x Iceland Gull hybrid, Sequim, Clallam County (Washington, USA), 10th February 2008 - copyright Steve Mlodinow
(photo ID: 2203)
The taxonomic treatment of Thayer's, Kumlien's and Iceland Gulls has been very confusing but currently many authorities treat Kumlien's (kumlieni) as a race of Iceland Gull (nominate glaucoides) and Thayer's (thayeri) as a distinct species. Thus "Iceland Gull" is sometimes used (as here) to refer to the whole species (i.e. glaucoides plus kumlieni) and sometimes to refer to just glaucoides (as distinct from Kumlien's).
I don't mind admitting that I was a bit surprised to see a claim of Thayer's Gull x Iceland Gull, even with the qualifying "presumed". There is enormous difficulty in separating the two species (at least from the perspective of a European who isn't a gull expert), there is uncertainty as to the range in variation of each taxa and there are unresolved questions over what the taxa even are (i.e. does the kumlieni race of Iceland Gull represent introgressive hybridisation between Thayer's Gull and nominate Iceland Gull?). But from Steve's much better informed and experienced perspective, thayeri and kumlieni are different taxa no matter how you slice it, and so there should still be intergrades or hybrids. And, he says, this is what he thinks one would look like. Well that seems fair to me, and I'm certainly in no place to argue against it!
presumed Thayer's Gull x Iceland Gull hybrid (same bird as in photo ID 2203 above), Sequim, Clallam County (Washington, USA), 10th February 2008 - copyright Steve Mlodinow
(photo ID: 2204)
For an overview of the situation with Thayer's, Kumlien's and Iceland Gulls, this page from the Gull Research Organisation is helpful.
Thayer's Gull Larus thayeri
Iceland Gull Larus glaucoides
Kumlien's Gull Larus glaucoides kumlieni