As you say, 1y mongolicus. However, I wouldn't place as much emphasis on the features you mention as I would on others. Leg colour is not so helpful at this time, as many of the heuglini show quite pale legs. The presence of pale tips to the primaries and anchor-like centres to the scapulars are features shared by other gull taxa, including heuglini and vegae. The contrastingly dark tertials are quite helpful at this time of year, though not so much early in the winter.
I find more useful features are the largely pale greater coverts with relatively narrow dark bars, the pale, greyish tinge to the mantle feathers and the complete lack of newly-moulted tertials, greater coverts and median coverts. The almost complete lack of undertail barring is also a useful feature.
In particular, 1y heuglini late in the winter can look rather mongolicus like, as their head and body becomes increasingly bleached white, while the mantle and scapulars can also become very faded, if they aren't replaced.
As so often with gulls, and birds in general, it is the combination of features that is important.
Nice photos, as usual !
GeoffC
[ Last edited by cgeoff at 8/03/2010 17:07 ]
