Vega Gulls  Larus vegae 
Feb. 25th 2011 Tokyo Imperial Palace Japan

A typical individual with heavy head streaking and black markings on P10-P5. 

Most individuals have head streaking even in February-March, though the extent is quite variable.

A somewhat unusual individual with white head and less extensive black markings on primaries.

The same individual as above. Note the somewhat cachinnans/thayeri-like wing pattern. 

The same individual as above.

The same individual as above.

Presumed Vega Gull with white head ? 
But this type of birds are often very problematic in separation from Mongolian Gull. In this case, lacking of black spot to the bill, mottling on hindneck widely connecting to upper back in late Feb, lacking of  black mark on P4, short-winged, stubby overall structure do not seem typical for Mongolian Gull.  Monglian Gull at the same site in 2009 and the best Mongolian Gull at Choshi in 2007 for comparison.