Went back to Rainham yesterday morning. Not as many birds around as on my two previous visits, so could only manage around 25 Yellow-legged Gulls (no Casps). After a few hours of seeing relatively little, I flirted with the idea of heading back home to bed but, on my final scan of the Thames, I spotted the Azorean-type floating aimlessly upriver towards me.
Over the next couple of hours, I only had reasonable views of it on the river and
over my head as it flew back towards the tip; it proved frustratingly
difficult to locate on the landfill itself, only on view for a
minute or two at the most! Here are some shots, including comparisons with both Herring and Lesser Black-backed.
Quite interesting to see how it has changed in appearance. The dark subterminal markings on the bill have intensified in the onset of winter plumage, and the amount head streaking has also increased. The secondaries and tail are in heavy moult; note how the outer tail feathers (that had quite a lot of black left in them back on 21st) have been dropped, leaving a rather messing looking beast. The immature underwing coverts have also been moulted through to white, adult-like feathers since 21st.
It looks pretty decent. Moult timing seems spot on. Primaries look fine. But something just bugs me, and as such I'm still unconvinced. I'd like to see it out of the water for longer and at closer range to get a real feel for structure and jizz though.
To compare moult/plumage, here are a couple of photographs of 'real' Azorean Gulls, taken in the archipelago this week by Rich Bonser. The similarities in moult of the tail and secondaries is striking.