This is an immature Larus argentatus in its 2nd cycle, photographed at the Larimer County landfill. It is not typical of the usual North American subspecies L. a. smithsonianus. The heavily marbled secondary coverts of the folded wing, and the slghtly darker gray of the mantle are suggestive of the Siberian subspecies L. a. vegae, which also breeds in northern Alaska. Comments?