1st.winter 'Common Gull'
showing some Mew Gull characeristics.
10th Feb. 2001 Choshi Chiba Japan

This individual shows a heavily barred dark rump,  mostly dark tail, and somewhat smith-like uniformly darkish overall coloration.

The unusual replaced central tail feather does not mean a part of regular molt.

Kamchatka Gull Larus canus kamtschatschensis