Yes, you are correct this is a first-winter gull.
This seems a good fit for taimyrensis Hueglin's Gull which is likely an integrade between Heuglin's and Vega Gull. The darker greater covert bar and pale 'windows' on the inner primaries is typical of taimyrensis observed in Japan. The pale base to the bill is more extensive than on typical taimyrensis (which general has all dark or just faint pale base) but might indicate this bird has a bit more Vega progeny than most Hueglin's Gull.
[ Last edited by brendank at 26/02/2012 23:54 ]
