Thursday, 22 December 2011

Quality trash birds

A third-winter Caspian Gull assumes a dominant stance. Note the adult-type wing-tip pattern with long pale tongues on the inner webs of the outer primaries and the extensive white on the tip of P10.
I picked up the same bird again a couple of hours later, circling the throng and eventually drifting south to drop down out of view somewhere near the river. Note the bill shape and pattern, and faint nape streaking.
After the white-knuckle ride that was birding in Colombia at the beginning of the month, it was back to reality earlier this week with a long-overdue gulling session at Rainham tip on the eastern edge of London. I haven't been able to get there much this winter, but knew there have been Caspians around (see Paul Hawkins's blog for in-the-hand shots) and wanted to see what might be in the offing in the new area now in use.

A different Caspian Gull, this one an adult, showed briefly among the thouands of gulls. Most of the time its feet were hidden among the rubbish, but on reviewing a couple of images I realised it was ringed. Unfortunately the code is not readable in the photos, but it will have acquired the ring elsewhere as Rainham birds are colour marked.
The same bird, showing another classic Caspo wing-tip pattern.
The result was an excellent, if cold, wet and muddy, morning among the best pile of stinking filth for miles around. Gull numbers weren't especially high, perhaps in the low thousands between the tip and the river, but in the current mild spell that's to be expected. Black-headed and European Herring Gulls were the most numerous, the latter including many of the larger, darker-mantled Scandinavian subspecies argentatus, and there were also decent numbers of Common and Lesser Black-backed Gulls (both graellsii and a few intermedius), and fewer Great Black-backeds. Best of the bunch by a country mile were three Caspians and a minimum of nine Yellow-legged Gulls (two first-winters, two second-winters, a fourth-winter and probably at least four adults). Also present and correct for another winter was the white European Herring Gull, cruelly immortalised with the ring number SH1T (you naughty ringers).

Caspian or Yellow-legged? The rather rich bare-part colours and pale iris of this bird might suggest the latter, though even on this perched view there looks to be a fair amount of white in the wing-tip ...
... while in flight the boldly white-tipped P10 and presence of pale tongues swings the pendulum towards Caspian. A wing-tip illustration in Olsen and Larsson (2003) suggests Yellow-legged Gull can also show a similar pattern, but I don't know how regularly this is seen on birds in Britain (compare figs 10 and 15 on pp26-27 of that work).
Adult and second-winter Yellow-legged Gulls, flanked by Herring, Great Black-backed and Black-headed Gulls.

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