1st winter
Vega Gulls Larus vegae, and some others
March 8th 2007 Choshi Chiba Japan

Note the typical tail pattern that looks intermediate just between Mongolian and American Herrig Gull.

Vega Gull(left), Slaty-backed Gull(right)
Note browner overall tone of the Slaty-backed Gull.

Unidentified 1st winter gull with dark tail.
Note the almost all-dark tail resembles Slaty-backed (or American Herring) Gull. The general impression looked intermediate between Vega and Slaty-backed Gull.

Same individual as above

1st winter gull with some features like Mongolian Gull .
Note the narrow tail band like Mongolian Gull.

Same individual as above
Note the extensive white on wing coverts and underparts like Mongolian Gull. But this individual looks fresher and darker overall compared to "good Mongolian Gulls" in this time of year.

Same individual as above

Links to other forms for comparison.
Slaty-backed Gulls
Slaty-backed Gulls
Mongolian Gull in Jan. 2006
Mongolian Gulls in Shanghai