Just before I headed back from Terceira on 31st August, I spotted this juvenile gull in the fish port at Praia da Vitoria. It was certainly one of the most bizarre looking creatures I'd seen for a long while - just why would a juvenile Azorean Gull (strictly speaking first-winter, as a couple of second generation scaps are coming through) have a pink based bill especially so close to its birth?
This bill colour gave a superficial resemblance to California Gull/Glaucous Gull for a passing moment. Completely at odds to Azorean Gull and certainly Yellow-legged Gull - though I've seen shots of a 'pink-billed' YLG from France in December. You'll see on the shots above that Azorean Gulls really do have a bit of a Nearctic feel, presuming that is what this bird is - particularly in flight if you look at the dark secondaries and dark based greater coverts. However rump, uppertail and undertail coverts as well as tail band are exactly what you expect for atlantis too. This bird also shows the dark shins that atlantis show.
Anyway, just be thankful this bird didn't end up out of range as it would have a heck of a lot of people scratching their heads. Here are a couple of typical juvenile atlantis from late August to compare it with: -
Thanks to Josh J, Peter Ad, Peter Al, Julian H and Kevin M for their input.