Herring Gull H-132058 1cy, November & December 2003, Westkapelle, the Netherlands (51.33N 03.25E).

This bird was ringed as fledged 1cy on September 17 2003 at Blankenberge, Belgium (51.19N 03.09E). All upper scapulars and most lower scapulars have been replaced for second generation feathers. Note the moult in the under-parts: the head, flank and upper breast are moulted to second generation feathers, somewhat colder brown-grey, while belly, flanks and vent still show the warmer brown juvenile feathers.
The partial autumn moult in argenteus (moult from juvenile plumage into so-called "first winter" plumage) includes the body and head feathers. This moult starts as soon as the nest is abandoned (late June) and continues until January. In general, the head turns paler on throat and forehead. The breast will turn paler as well. The feathers on belly and vent will still be juvenile in most 1cy argenteus by November. From July onwards, the mantle and upper scapulars are moulted to second generation feathers, showing an anchor pattern and a dark base. The lowest row of scapulars are still juvenile by March in most 2cy birds (contra e.g. michahellis). The notched pattern of the juvenile scapulars is repeated on the juvenile lesser, lower lesser and median coverts, although the medians have paler centres. The juvenile greater coverts show a 'piano-key' pattern; on the outer greater coverts as well. The tertials have an obvious notched pale fringe and transversal bar. 
The juvenile wing-coverts, rectrices and remiges start to bleach and show wear in the fringes from September onwards. 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.

top image: H-132058 1cy, November 02 2003, Westkapelle, the Netherlands.

Moult score: visible greater coverts 1-15 juvenile, median coverts 1-16 juvenile; lower lesser coverts all juvenile; lesser coverts juvenile (80% visible). Upper scapulars 100% second generation; lower scapulars 75-99% second generation. Tertials 1-6 juvenile. 

above: H-132058 1cy, November 15 2003, Westkapelle, the Netherlands.

bottom image: H-132058 1cy, December 14 2003, Westkapelle, the Netherlands.