A few more
Edit: Ooops, Galway, didn't see it's in the title!
Probably a young American Herring Gull for me...
Sure is what it looks like - nice bird Dermot, congrats!
First-winter Thayers Gull, probably a male. I finally got decent views of this bird, even better than a Smiths!
A very intriguing and baffling bird Dermot - of that there is no doubt. I have reservations though that it is a pure thayeri and still feel that many of the apparent features are far more indicative of North American Herring Gull. It seems far too dark for my liking for a juvenile Thayer's - even the smallest, darkest male - and does not have the tail pattern I would expect nor the scalloped affect on the scapulars and upper wing covert feathers.
Obviously, you have spent a lot of time studying this gull and have done excellently well in the very informative and qualititive set of images you have amassed - so I bow down to your investigations and findings
This bird is rather reminiscent of a bird claimed as (and accepted as) Thayer's Gull in County Mayo, sharing many pro-Smithsonianus features. It is much darker however and has an immaculate 'carpet' of smooth breast feathering.
Well done for sticking with it
All the very best
Many thanks for sending me the Japanese links - if these birds are 'true, pure' Thayer's Gulls then there seems little reason to deny your Galway juvenile this labelling. I have added the links along with your images on my Rare Bird Alert blog and will forward you any comments I receive. Martin Garner certainly agrees with your synopsis reading into his excitement.
I had the same doubts as Lee and my immediate impression was of a small-billed smithsonianus. However, loooking at the last image, with a better colour balance, although this is a variable feature in young thayeri, together with pale edged and pattern of outer primaries, which differ from smithsonianus. Bunched primaries are darker than tertials (usually also than tail). In a funny way I have the feeling that the scapulars looks a bit large for thayeri.
Spoke too soon, it seems!