Lower Rivington gull roost

[ianball]

Fantastic couple of hours watching the roost grow till 3.45pm when there were approx 6-7000 birds, mainly BH Gull and Common Gull.
Photo is a record shot of possible 3rd W Caspian Gull

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Picked up at first due to all white head alongside Herring Gull. Noted that the bill was very elongate and the forehead sloping/long neck, and not the large flat headed shape of the Yellow legged Gulls seen this afternoon. The back also sat very flat which is mentioned in Olsen and Larsson (Gulls ID). A more slender bird than surrounding Herring Gull.

Edit - 1 adult and 2 3rd Winter Yellow Legged Gulls observed - noticeably bulkier than Herring and LBB Gulls, and back colouration slightly darker than Herring. Flat head was noticeable as were the primary patterns. Have reviewed field notes and bill colouration to aid in the ageing of the older birds. A second winter YL Gull also seen, swimming and interacting with one of the 3rd W birds.

Several Argentatus Herring Gull in with the 'normal' Argenteus birds. They were real brutes... one perched bird on the wall dwarfing the LBB Gulls it was sat with!

Also seen were Mediterranean Gull and Great Black Backed Gull.

YL, GBB and Med Gulls take me to 57. I'm 99.9% confident on the Caspian Gull but opinions welcome.

[Neil Southworth]

The photograph's not really clear enough to make an identification, Ian, and Caspian Gull is still a description species. I would be worried about the bird's relatively small size and pale mantle, which suggest argenteus, many of which are now in summer plumage and therefore white-headed. The image doesn't show the wing tips precluding any aid to id from that. Do you have any other images?

[ianball]

Edited response (11pm)

Thanks for the reply Neil. I'm very confident about the YL Gulls, in fact the full adult bird was almost the only large Gull on the water when I arrived at 2pm. It was seen well in flight as well as at rest. Yes there were some clean Argenteus Herring Gulls but they were noticeably smaller and less bulky than the LBB and Argentatus Herring Gulls around. The mantle colour of the YL Gulls was noticeably darker, similar to the Common Gulls.
At about 3.15pm I came across the possible Caspian Gull. As I have said the shape of the bird stood out after the 'white' head had got my interest. I certainly wouldn't say 'many' Argenteus Herring Gulls have clearly white heads right now... Of the c100 Herring 'type' gulls viewed, single figures only had either fully clean heads or faint streaking. I think I mentioned before on another thread about moult times and the end of January and into February is the norm for Argenteus (from literature).
The photo really was just added as a 'record' and is the best one I have... every time I had the telescope set on the bird and put my phone adaptor on the Herring Gulls would always move in front! Regarding mantle colour, Caspian Gull does have more overlap with Herring Gull and is not always darker, plus size wise they can be similar too - so I'm not worried about that. The photo really does not do the bird justice... the bill was noticeably elongate compared to the Herring Gull, the head shape very different as well, adding to the elongate shape. The primaries were predominantly dark with only small fine white primary spots. I was unable to judge p10 even though the bird did flap its wings several times. In referencing literature I believe that this could be a 4th Winter bird, very similar to one in the British Birds report, as the wings had very little 'browner' feathers but the black markings on the bill, again the literature say there can be a lot of overlap between plumages.
Apologies for the length of my reply. I've had my nose in the literature all evening and studied numerous photos along with the British Birds ID papers. I will be happy to do a report based on what I've seen, the jizz of the bird was very different to all the other large gulls present, and much of the literature does focus more on this rather than plumage features that can overlap. An interesting bird.

[ianball]

There is a really interesting summary at the end of the British Birds report which I will link to when submitting my report. These are shown below for general structure and 3rd/4th Winter birds. The structural features that I observed and can be seen even in the record photo are highlighted in the first part. The second part notes that 3rd/4th W birds can have paler mantle colour than adults. Apologies if I am going on but I have been reading up fully to help prepare a report. There are also currently good numbers of YL and Caspian Gulls currently in the NW (e.g. Audenshaw)...

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