This is what I have been doing all day - 1st draft of a description
I was sea-watching, from my 3rd floor sea-front office and half-heartedy scanning though an estimated 14,000 large Larus spp which were roosting on the water just offshore. The gulls were facing into a cold easterly wind and where hence all head on, making scanning through them a near impossible task. Just before 11am there was a disturbance in the roost to the east of me and about 4000 large gulls took to the air. I was primarily looking for a 1st winter Glaucous Gull which had been seen in the area as well as trying to relocate putative 3rd winter Caspian Gull that I’d had nearly but not quite conclusive views of on the last set of tides. Since a good number of the Gulls were now in flight, I switched to bins (8x42) since I fancied my chances of pulling out the Glauc with a wider angle view. Almost immediately I noticed a phenomenally dark 1st winter Gull with an apparently all dark tail and a paler inner primary panel.
The bird flew about 300 yards to the right of me and landed on the sea again. I could see it easily with bins, since it was so large and dark. I set up a scope (48x80) and was able to get a good view of the bird. I was able to see the bill shape and colouration well, had checked the underparts, including the vent pattern, tertials and greater-coverts. I thought I had enough to ID the bird as American Herring Gull, so I went downstairs to find my phone so I could put the news out, and my camera so I could get some record shots.
By the time I got back upstairs the gull flock had relocated further out to sea and further west. I looked for another hour and failed to locate the bird. At about 2.30pm, with the tide now dropping, a large Gull roost developed on the beach. I went through around 8000 gulls before I found a huge dark gull almost opposite the house. It was asleep and largely head on, so I can’t confirm that it was the same bird, but it was larger than nearby Herring Gulls and approaching smaller GBBGs. It was evenly dark underneath and had rather bright pink legs. It was too far out to see any details of the upperpart makings. I managed an appalling photo of the bird, then went down to pick up my phone again. When I got back upstairs, the whole flock had moved out to the low tide edge.
Description:
Jizz/size: A large and stocky gull, larger than all the predominately argenteus Herring Gulls. I didn’t see it alongside one, but I got the impression that it was of big argentatus proportions. I saw it close to GBBGs and it was close to the smallest individuals. “Mean” looking bird, with a long bill, the Glaucous Gull impression was emphasised by the colouration. The primary projection was similar to Herring Gulls – hence shorter than YLG/LBBG etc and there was quite a prominent tertial step. The legs on the second view, appeared short and strong.
Soft parts: The bill was pink based and the bill tip was black – quite like a 1st w Glaucous Gull, though will less sharp differentiation. It was possibly longer (but not strikingly) than the surrounding Herring Gulls. The legs were seen to be rather bright pink on the second view. It just shows in the photo if you use your imagination.
Upperparts: In flight the tail appeared all dark (near black) I can’t for absolute certain say that there was no fine barring at the very base of the TFs, but if there was any barring present on the base of the tail, it was similar to upper tail coverts since there was a contrast line. The rump was only slightly paler than the very dark upperparts and in flight I got an impression very like a juv Pomarine Skua, though I didn’t resolve barring with bins. Tertials: I looked carefully at the tertials – they were rather uniform, with just a narrow paler crescent at the tips. I could see clear notches on 1st W Herring Gulls alongside. The greater coverts were dark based, but there some paler marks towards the tips (distal 1/4) which formed a paler bar between the very dark bases and the secondaries. I also got the impression in flight that there was a thinner than expected mid-wing panel. The outer primaries and secondaries were near black and I could see no mirrors/apical spots. Mantle/Scaps/lesser coverts: Rather dark and more uniform than nearby Herring Gulls, though I didn’t get as far as looking at them individually. Head also rather dark.
Underparts: The entire underparts were rather dark. The neck, chest and as much of the belly as I could see on the water were apparently uniformly dark, slightly grey brown. I could see mottling on all the other juv Gulls at the same range. I looked at the vent and could see that it was slightly paler than middle of the breast and had very fine pale barring (though was predominately dark brown). On the second view I could see that the underside of the belly was also dark and that the vent was only slightly paler (though it was too far to resolve detail).
I have a couple of scruffy drawings to scan