Mongolian Gull Larus cachinnans? mongolicus
March 25th 2005 Choshi Chiba Japan.

'White-headed birds' were increasing, though many Vega Gulls still showed complete winter plumage. Some of them might be summer plumage Vega Gulls, and some others might be Mongolian Gulls. Identifications for adults in late March are not easy.

A presumed Mongolian Gull. The bill has a narrow black line that ranges over both mandibles.

The gray on upperparts looked slightly paler than most Vega Gulls (about Kodak 5.5?, similar to some Thayer's Gulls in my impression) . And the leg color also looked paler. The farthest bird in this image is a typical Vega Gull.

The same individual flying above the mixed flock.

The outer web of P4 has a black marking, though it seems to be very small.

A presumed Vega Gull Larus vegae turning into summer plumage
The face was not completely white. The black marking on P5 is very narrow. No black marking on P4. The left bird is a typical winter plumage Vega Gull.

Summer plumage Vega Gull?
I could not see its wing pattern. Many birds on the day didn't move an inch because of the strong wind.