Gulls in Mai Po, Hong Kong    March 10th 2001, Photos by Kwan
Adut winter/summer Heuglin's Gull L.heuglini taimyrensis
Hong Kong is one of the main wintering place for taimyrensis.
The primaries are not fully grown in spite of March.
Checking their mantle shades exactly is 
not easy without other species, Black-tailed Gull etc. 
But at least, these birds's  mantles seem 
paler than Slaty-backed Gull on average.
The left  bird in background shows darker mantle,
and looks like a darker-taimyrensis or heuglini.
The head streaking is fine and sharp, different from cloud-like marking of typical Vega Gulls,
but often is similar to some winter plumage mongolicus too.

 1st-winter/summer Mongolian Gull
with extremely whitish appearance.
1st-winter Glaucous Gull
1st-winter Black-tailed Gull