Lesser Black-backed Gull 3CY, May 29 2017, Heemskerk, the Netherlands.
Bird returned from wintering grounds with arrested moult in primaries. Current situation: P1-P5 3rd gen replaced last winter, P6-P10 old 2nd gen. All secondaries replaced as well last winter, now 3rd gen.
Advanced tail, almost completely white.
Last image: note bird in background, also showing arrested primary moult.
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