I took this photo on 25 January 2011 at Choshi in Japan and it has been bugging me ever since. I am not very experienced with Asian gulls, so I would appreciate some help with the id. My hunch is that it *might* be a small (female?) first winter Slaty-backed as the plumage tones (in particular the base colour, tertials and primary colouration) and rather short-winged profile seem to fit. However, it does not look typical in terms of bulk for this species, and the rounded head is troubling me, so I may be off-beam.
From looking at images on the excellent Japanese Gull site, I don't think it is a Vega or Glaucous-winged but can't seem to find a good fit.
Grateful for any help from the larophiles on here...
Thanks in advance.