Adult Winter Thayer's Gull 　Larus thayeri

P10-5. Note the underwing color and P9 pattern. With 2w Slaty-backed Gull.

With 2w Slaty-backed Gull(background) and 1w Slaty backed Gull(foreground).

Iris is dark. Note the big eye and small bill.

From Mori Hokkaido Japan. December 31.