4th winter
Thayer's/Kumlien's Gull Larus thayeri / L. glaucoides kumlieni
January 30th and February 28th 2012  Choshi Chiba Japan

This gull also seems to be the same individual as another one considered as kumlieni in 2009 ('Sangou'). This also has grown into a darker bird than we expected, and currently looks like a hybrid/intergrade between thayeri and kumlieni. We will keep our eyes open to watch  next year whether this individual will get paler than this or not.

The wing pattern is quite subtle. The dark markings of the left wing look 5 pieces, 10-P6. But on the left wing, the outer web of P5 (-6th from the outermost) has a tiny dot. The dark band of P6 is grayish, and is divided by a white shaft. White mirror on P9 slightly spreads out to the outer web on the left wing, but is restricted to the inner web on the right wing.  

The same individual on February 28th.

Comparison with Vega Gulls and a 'Taimyr Gull'.

Looks very like kumlieni in this shot.

1st winter in 2009 (left), 4th winter in 2012 (right), presumed the same individual.

For comparison: Kumlien's Iceland Gull  Larus glaucoides kumleni  at Niagara Canada in 2005.