Ring-billed Gull L. delawarensis
January 19th 2002 Hasaki  Ibaragi Japan
-located on the other side of Choshi, across the Tonegawa-river.

This is the first Ring-billed Gull for Japan.

Note the paler mantle.The tone often fits paler individuals of Kamtchatka Gull, and looks darker than that of Black-headed Gulls. But, similar situations can be seen in RBG photographs taken in U.S or Europe, and seem to be quite normal for RBG.

Compare their P10 mirrors. And note the bulkier body structure of the RBG, though some larger Kamtchatka Gulls can show similar structure as well.

This individual often shows squarish head shape when it is facing to me. The white tertial crescent can appear wider when the feathers are spread, because it is wider in lower(outer) feathers even in RBGs.  But typically, Kamchatka Gulls show much wider, big white crescent.

The Same Bird on the Next Day