Monday, 6 October 2014

interesting Lesser Black-backed Gulls on the Adur (6 October 2014)?

I took advantage of poor forecast to drive into work enabling me to call in at the Adur on my way home.  No sign of the Caspian Gull but two colour-ringed Lesser Black-backs, one seemingly from Denmark. Also a very striking looking adult Lesser Black-back which appeared to show features of Baltic Gull (L. f. fuscus) , but these are even harder than Caspian Gulls and it did not have the potential clincher - a ring!  Also on the Adur the Wigeon, a Curlew and Kingfisher were still present.
putative fuscus Lesser Black-backed Gull on the Adur
features shown by adult fuscus are small size, slim build with attenuated rear end, very dark mantle which primaries do not contrast with, single mirror on p10, small rounded white head with no streaking, long thin bill and shorter legs.  This image does not show the last feature very well (and p10 isn't visible, but is in a lower image) and note the rounded head.  Unfortunately intermedius can show these features too although this was a most striking individual (otherwise I doubt if I would have noticed it)
note the single mirror on p10.  This image just about shows on the far wing the well-marked border between the large white tips to p1-p4 and the (very) small white tips to p5-10 mentioned in the Advanced Bird ID Guide.  It also mentions primary moult normally starting in August when usually only p1 and p2 are moulted when suspended until in the wintering area in Africa.  This appears to be evident on the nearer wing.  Also a distinct lack of head streaking (noted in the Advanced Bird ID Guide for fuscus up to September/October)
note small size compared to Herring and ringed graellsii Lesser Black-back Gulls behind.  Note also pure white head

compared to the intermedius behind note the small size, pure white head, bright (slighly shorter) legs, very elongated rear and darker mantle.  Note too the larger leg of a Greater Black-back in the top of the image.  This bird shows it self a bit better in the next image ...

my only image with a Greater Black-back nearby. Not the best comparison but note the very small size and darker mantle 
the legs look reassuringly short in this image and the bill long and slender
shows the long wings very well, so long it was a wonder the bird didn't fall backwards.  This image is rather over-exposed in the low evening sun and shows rather more contrast/colour bleaching on the upperparts than was apparent in the field (and the other images) although fuscus can show a brown wash
adult intermedius and Greater Black-backed Gull from above images.  A pity the fuscus type wasn't in the front to show the step change in size.  Note intermedius primaries darker than mantle with large mirrors (c.f. fuscus type above), streaked head and very washed out legs
colour-ringed Lesser Black-backed Gull (N.FNU), ringed as a chick on Havergate Island, Suffolk on 12 July so graellsii.

colour-ringed Lesser Black-backed Gull (V1VN), probably from Denmark.  A darker bird than the above but both were noticably bigger and heavier than the putative fuscus
longer legged too?

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