Herring Gull L4 2cy (argenteus), March & November 2004, November 2008, Amsterdam, the Netherlands (52.21N-04.52E). Pictures Ruud Altenburg.

Ringed as pullus June 24 2003 in the Netherlands by Roland-Jan Buijs, mint-green L4. An individual with slightly delayed scapular moult for Dutch birds. The moulted scapulars show a pale base and transversal bars. Note the moult stage in the under-parts and the head.

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, compared to the juvenile plumage. The second generation feathers on the breast are paler as well. The feathers on the vent and the under-tail coverts are still juvenile in most 2cy argenteus by January. From July onwards, after leaving the nest, the mantle and upper scapulars were moulted last year to second generation feathers, showing an anchor pattern and a dark base. The lowest row of scapulars, especially the rear feathers, are still juvenile or actively moulted by March in most 2cy birds (contra e.g. michahellis, which has finished the replacement in the lowest row). The notched pattern of the juvenile tertials, lesser, lower lesser and median coverts is not very obvious anymore by February, as the white parts are largely worn away. The juvenile greater coverts show a 'piano-key' pattern in argenteus; on the outer greater coverts as well. 
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.

below: L4 2cy (argenteus), November 28 2004, Amsterdam, the Netherlands.

A typical argenteus, with the new scapulars plain adult-like grey. The bill is still all dark. Note the rather brown second generation primaries lacking the mirror on P10. Compared to Scandinavian argentatus, the general impression resembles argentatus in 4cy, which also show an almost complete grey scapular region and single grey feathers in the tertials, inner greater coverts and a few lesser coverts.
This Dutch individual has moulted a few tertials and wing-coverts in the partial autumn moult as 2cy bird. The new feathers have fresh fringes and tips and are adult-like grey; also the patterns are less defined.

Herring Gull L4 6cy (argenteus), November 28 2008, Amsterdam, the Netherlands. Picture: Ruud Altenburg.

Ringing data: ringed as female pullus at Moerdijk, 24 June 2003 by R-J Buijs. Recorded at Westerpark, Amsterdam about 50 times, almost no other locations.