Herring Gull H-131045 2cy (argenteus), September 18 2004, IJmuiden, the Netherlands (52.27N-04.33E).

A 2cy Herring Gull, maybe from the argenteus population in Belgium, ringed Bruxelles H131045. P9 tip just over P8.

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. 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. In argenteus, some new scapulars may appear adult-like pale grey, but most new feathers will show an anchor pattern and this still applies on the new feathers in September. By September, 2cy argenteus is actively moulting the lowest scapulars, but in the mean time, the upper scapulars may be moulted again as well. Fresh feathers can be recognized by the buffish centres. 

From 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.
From late April to September, argenteus replace the wing-coverts and tertials, finishing with the central greater coverts and outer lesser coverts. By September, 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.

Bruxelles H-131045 has primary P9 fully grown and the partial wing-covert moult has started. The upper tertial, the inner greater and the inner median coverts have been replaced recently. A few new scapulars are growing in, now showing a grey base. There is a broad tail-band on the new rectrices. Note the fine streaking on the head-feathers and note the pink base of the bill.