Mongolian Gull Larus c? mongolicus
November 30th 2004 Choshi Chiba Japan
Note the somewhat 'cachinnans-like', longish general structure and the paler legs.
Compare the head-streaking with the typical Vega Gull in the rear-left. Vega Gulls seem to tend to have brighter bill in this time of year, though it can be variable. And note also that the Vega Gull behind the Mongolian Gull still shows old P10s to the both wings.