1st-winter to summer
Heuglin's Gull 
Larus heuglini taimyrensis,
Sakawagawa river,
Odawara, Kanagawa,
April 16th 2001
This image shows typical taimyrensis posture unlike vegae. 
Head shape often looks triangular, when it shrug its shoulder.
( lower forehead, and peaked back of the head.) 
Primaries are longer than a vegae below. 
I guess Lesser blacke-backed gulls also often show such (or more extreme) postures.
Taimyrensis (left ) with Vegae (right). 
Note the smaller bill. 

Note the scaly coverts though it doesn't appear so obviously strong in this case.
The body color is rather faded than it in mid-winter.