Heuglin's Gull L. heuglini taimyrensis 
January 28th 2001 Choshi Chiba Japan
A 1st winter taimyrensis with a vegae. Note the lighter structure, relatively long wings, small bill and LBBG-like impression overall. Its coverts, scapulars and tertials show less white, compared with Vega Gulls. In flight, the inner primaries were pretty dark (but not completely dark like most LBBGs), and did not form distinctive pale windows.
Compare its bill size and greater coverts with the Vega Gull.

Vega Gull L. vegae
Vega Gull has standard features among Large Gulls in Japan. Its structure looks stouter than taimyrensis, lighter than Slaty-Backed Gull. And its coloration is darker than mongolicus, paler than taimyrensis and smithsonianus.