Candidates of Monglian Gull ?

November 29th 2006 Choshi Chiba Japan.
This individual has many characteristics that suggest Mongolian Gull (whitish head, black markings on bill, finished primary molt in November, palish pink legs), and looks like a good Mongolian Gull in this image.

But in this angle brown largish spots seem to be extending to lower breast, and somewhat recall Vega Gull. The general structure looks relatively stubby.

And its P4 lacks black marking. This combination of features does not seem to be typical for Mongolian Gull. Although all features might be within the variation range of Mongolian Gull, such birds often puzzle us, especially in Japan just outside main wintering range of Mongolian Gull.

November 29th 2006 Choshi Chiba Japan.
This individual has white belly and contrasty overall coloration, and can be a candidate of Mongolian Gull. But it is almost completely juvenile plumage, and the tail pattern is not so typical for Mongolian Gull ( the tail band is narrow, but with dense bars at base). 1st cycle birds are also variable, and often let us hesitate to conclude.