Pallas's gull

First winter male?
This is a very large gull, being easily the world's largest black-headed gull and the third largest species of gull in the world, after the great black-backed gull and the glaucous gull. Summer adults are unmistakable, since no other gull of this size has a black hood. The adults have grey wings and back, with conspicuous white "mirrors" at the wing tips. The legs are yellow and the bill is red. In all other plumages, a dark mask through the eye indicates the vestiges of the hood. The call is a deep aargh cry. Young birds attain largely grey upperparts quite rapidly, but they take four years to reach maturity.

A full grown adult can be seen here: http://www.projectnoah.org/spottings/2044726002