An excellent set of photos and it is very interesting to see!
This is the type of bird that often gets labeled as Slaty-backed Gulls in Hong Kong. However, to me this bird is not a good fit with Slaty-backed Gull. The structure is not typical for Slaty-backed Gulls. This bird has a rather round "dove"-like head whereas Slaty-backed Gull looks rather block-headed and on this bird the folded wingtips extend rather far past the tail whereas in Slaty-backed that tends to be rather short. Also troubling to me is flecking present on the coverts. While highly variable, on Slaty-backed Gull the coverts typically are more smoothly brown. Additionally, the color tone of the mantle on first-year Slaty-backed Gulls is rather rusty and this feature is completely absent from this bird.
Birds like this seem to me to be a better fit for Vega Gull or least I suspect have some Vega Gull ancestry.
One feature that does seem to point toward Slaty-backed Gull is the rather solid brown tertials. However, the tertials on this bird are heavily worn and there does seem to be some white-fringing to the tertials (which would suggest Vega).
Flight photos of this bird would be very interesting to see if available.
[ Last edited by brendank at 13/02/2012 23:45 ]
