Thursday, 29 December 2011

Gulls galore

Adult gull showing characters recalling the atlantis form of Yellow-legged Gull (or Azores Gull, reflecting the range of true atlantis). This is the second such bird I've seen in London. Note the pattern and density of head streaking.
I managed to squeeze in the last gulling session of the year at my local study site yesterday, and it was well worth it on a number of counts. Top billing potentially goes to the streaky-headed adult Yellow-legged type which was reminiscent of the form atlantis. This distinctive subspecies from the Azores - arguably a potential split - is more strongly streaked on the head than nominate michahellis Yellow-legged Gull in the autumn, often appearing hooded at any distance. I have seen many thousands of atlantis on the Azores over the course of nine visits, and this bird immediately brought their distinctive heavily marked appearance to mind.

Take your pick - a sample of head patterns on atlantis gulls from the Azores.
The pattern of streaking is not the most typical, however, as many (at least those I've seen in October) seem less well marked on the nape and sometimes more so on the 'snout', so that the hood is neater and more 'even' in appearance. However, I have also seen birds like this, and the pattern fits within the description provided by Olsen and Larsson (2003): "In winter (Aug-Nov/Dec), head more strongly patterned than in michahellis, similar to Herring and Lesser Black-backed, but streaking even denser around eye and below gape, but fainter on hindneck. Azores (and a few Madeiran) birds have even stronger head-spotting and look dark-hooded at distance; hindneck sometimes unstreaked. Head is mainly white with narrow dark streaks around eye and well-scattered brown spots on crown, hindneck and ear-coverts (Madeira and Canary Islands populations)."

The red orbital ring is just about visible in this shot, as is the very pale iris.
Also notable about this bird was the mantle colour, which was a distinctly dark ash-grey - edging a little more towards the palest graellsii Lesser Black-backeds (one of which is perched in front, above). Unfortunately, it was not seen in flight, although some images of it preening give an indication of the wing-tip pattern:

The bird wasn't seen in flight, but here's one shot showing some of the wing-tip pattern.
I wonder what this bird would have looked like two months ago? Presumably even more streaked, and by extension more dark-hooded. Some Azores adults are white-headed even in October, as are the great majority of michahellis by December. A photo of a streaky-headed adult michahellis, taken in November in Worcestershire, is mentioned as "extraordinary" on the Gull Research Organisation website. I have already had some interesting feedback from Peter Alfrey and am taking more soundings on variation in michahellis to try and establish whether the Rainham bird could possibly fall within that, or whether it is a better match for atlantis. More soon, I hope.

Adult michahellis Yellow-legged Gull yesterday - in typically white-headed condition in late December.
Among the many other interesting larids yesterday was a striking, long-billed and rather dark first-winter Caspian Gull (below). By amazing coincidence, among all the thousands of gulls in the area, it was also found independently and photographed by Paul Hawkins - small world:

Smart it may be, but this first-winter Caspian Gull is already looking heavily worn on the wing coverts.
A second-winter Yellow-legged Gull assumes the position.

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