Herring Gull H - 117779 2cy (argenteus), October 24 2002, Boulogne-sur-Mer, France (50.43N-01.37E).

A 2cy argenteus, ring number Bruxelles H - 117779, ringed as pullus on July 20 2001 at Zeebrugge (51.20N 03.11E).
From late April onwards, argenteus has a complete moult during summer to so-called "second winter" plumage. This complete moult will be finished by October and overlaps with the partial autumn moult which starts in September and often include scapulars, a few inner wing-coverts and upper tertials. The head has been moulted in July-August and shows neat fine streaking by October. The under-parts and rump are pale, mottled with brown. From mid-May, the scapulars and mantle were replaced for third generation feathers, starting with the replacement of the lower upper scapulars. The pattern of the third generation scapulars is more or less similar to the anchor pattern of the second generation feathers. By October, argenteus acquire some new adult-like pale grey scapulars. 

From early April, the inner primaries were shed and new second generation primaries grown in. On average, the last juvenile primary (P10) was shed in the first week of August. The majority of argenteus complete the primary moult by the first week of October, when the new second generation P10 will be fully grown. The new primaries are dark with a tiny pale tip on the fresh flight-feathers. The four inner primaries show an extensive pale window, as both inner and outer-web are pale greyish white-brown, contrasting with the outer-wing. A pale inner-web can still be found in P7.
The second generation tail-feathers show a clear-cut blackish tail-band with only isolated blackish markings on the white basal half.
By early October, argenteus finish the complete moult, with the central greater coverts and outer lesser coverts moulted last. Between September and November, the average 2cy argenteus start a simultaneous partial autumn moult in the wing-coverts, including the upper tertials, some median and lower lesser coverts and often the inner greater coverts.

This Belgian 2cy argenteus is illustrative for argenteus which started the partial moult: tertial #1 is replaced. All wing-coverts are old second generation feathers, except lower lesser coverts #3-4. The fresh lower upper scapulars have a grey base.