First winter Vega Gull Larus vegae
Choshi Chiba Japan, April 7th 2001.
Vegae often shows somewhat shorter-winged  structure, and has browner impression compared with mongolicus.
And often base of  first winter scapulars looks rather darker.
Under tail-coverts typically look spotted unlike typical smithsonianus that usually show barred under tail coverts.
 Width of tail-band is usually intermediate between mongolicus and smithsonianus on average.