Herring Gull xxx4248 2cy (argenteus), January 29 2006, IJmuiden, the Netherlands (52.27N-04.33E). Picture Robert Heemskerk.

Argenteus has a partial moult of head and body-feathers in spring. This partial moult starts in January and ends by May, leaving birds in so-called "first summer" plumage. The head and under-parts resemble the pattern in 1cy birds, although the head and breast turn much paler by June. The lowest scapulars may still be moulted in this period, showing a buffish tone and a neat pale fringe. The adjacent juvenile rear lowest scapulars are very worn by February.
The juvenile tertials, lesser, lower lesser and median coverts have a notched pattern, strongly worn by February. The juvenile greater coverts show a 'piano-key' pattern; in argenteus on the outer greater coverts as well. The juvenile tertials have an obvious notched pale fringe and transversal bar. 
The juvenile wing-coverts, rectrices and remiges are bleached and show wear in the fringes. The secondaries, primaries and primary coverts are dark with a small white tip, but the juvenile inner primaries show an obvious pale window, prominent from below and above. The under-wing is rather uniform grey-brown patterned. The tail has a broad sub-terminal band and isolated dark bars on the basal half. The iris is dark, the bill is blackish, sometimes with a paler base, and the legs are flesh-pink.
Normally argenteus shows much more wear in the coverts, tertials and scapulars than Scandinavian argentatus. Furthermore, argenteus has an on average higher moult score in the scapulars, with quite some argentatus still show many juvenile scapulars. Differences in moult score in other feather tracts is not expected; both argentatus and argenteus retain their juvenile wing-coverts, remiges and rectrices well into spring.

mplete moult, all wing-coverts have been replaced, most to plain grey feathers although there may be diffuse patterns. Such immature patterns can often be found in the lower tertials, greater coverts and outer lesser coverts (the carpal edge).
During the summer, the primaries were moulted to third generation. The first inner primaries are dropped by late May and the outer primary P10 will be dropped by late August. The primary moult is completed by late-October or November in argenteus,