(4 images) Herring Gull H - 117774 (argenteus), October 2001 - February 2003, Boulogne/Mer, France (50.43N-01.37E).

Ringed in Belgium as pullus, with metal ring Bruxelles H-117774, ringed as pullus on July 16 2001 at Zeebrugge (51.20N 03.11E). This bird was rediscovered in January 2002, at the same spot. Compare moult pace and wear in the white parts of the feathers. An individual with no scapulars moulted for second generation 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.

image below: H - 117774 1cy, October 01 2001, Boulogne/Mer, France (50.43N-01.37E).

photo above: H - 117774 1cy, October 01 2001, Boulogne/Mer, France (50.43N-01.37E).

2 photo's below: H - 117774, 2cy, January 04 2002, Boulogne/Mer, France (50.43N-01.37E).

Again H-117774. In the background, another Belgian ringed 2cy argenteus. Compare moult pace and wear in the feathers (severe wear in the white notches of the wing-coverts and tertials).

image below: H-117774 3cy, February 07 2003, Boulogne/Mer, France (50.43N-01.37E).

A typical 3cy argenteus ringed in Belgium: Bruxelles H-117774. The blackish-brown second generation primaries lack a mirror on P10. The second generation tail has a broad dark tail-band.
The new scapulars are more or less uniform pale grey, contrasting with the old patterned brownish feathers left in the rear upper and lower scapulars.
This Belgian individual has moulted tertials and a few wing-coverts have been replaced to third generation feathers in the partial autumn moult: the two upper tertials are obvious fresher than the adjacent feathers. The greater covert #1 and median covert #1 have been replaced as well. The new feathers have fresh fringes and tips compared to the adjacent feathers, but the patterns of these new tertials and greater covert is very similar to the second generation feathers, although they are typically grey-based with faint sub-terminal markings and a pronounced shaft streak.

image below: H-1177743cy, March 15-16 2003, Boulogne/Mer, France (50.42N,1.34E).

A typical argenteus, with most scapulars plain adult-like grey, contrasting with the barred lesser coverts and almost creating a saddle effect. The bill is typical for 3cy birds in March, pinkish base and a broad bill-band.
The moult-stage is sometimes difficult to interpret in 3cy argenteus by March. The scapulars are more or less uniform grey with just a few patterned brownish feathers left. Many grey scapulars appear abraded at the fringes already, especially in the upper scapulars.
This Belgian individual has moulted a few tertials and wing-coverts as is described in the February caption.

3cy argenteus has a partial moult in spring. It starts in January and is completed by April, leaving birds in so-called "second summer" plumage. The head turns white, especially on throat, breast and belly. By April, the scapulars and mantle will show many adult-like grey feathers, often creating a contrasting "grey saddle", as most of the wing-coverts (especially the lesser coverts) are still barred. The old second generation wing-coverts start to fade and the fringes wear off. 
The iris and base of the bill turn pale yellow, although some individuals show a warm amber iris. The bill shows some red on the gonydeal angle and it still shows an obvious dark bill-band.