(2 images) Herring Gull 5T 2cy (argenteus), August 28 2008, IJmuiden, the Netherlands.

A 2cy argenteus, ringed as pullus on July 02 2007 at Vlissingen-Oost, Zeeland (southern delta of the Netherlands) by Roland-Jan Buijs.

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 appears white from May to July, will be moulted by July-August and will show neat fine streaking by October. The under-parts and rump turns pale, mottled with brown. From mid-April, the scapulars and mantle are replaced by 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, but they can be recognized by the warm buffish tone and neat white fringe as long as the feathers are fresh. In the second generation scapulars, the fringes are often worn away (especially in the upper scapulars). 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.

From early April, the inner primaries are shed and new second generation primaries grown in. The last juvenile primary (P10) will be shed by the first week of August. The majority of argenteus complete the primary moult by the first week of October, with a new second generation P10 fully grown. The new primaries are dark with a tiny pale tip on the fresh flight-feathers. Again, 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 will show a clear-cut blackish tail-band with only isolated blackish markings on the white basal half.
From late April, argenteus will replace the wing-coverts and tertials, starting with the median coverts, upper tertials and innermost greater coverts. The fresh feathers will be buffish-based with an obvious barred pattern. By July, the warm tones of the first moulted feathers are faded to plain white, leaving a contrasting barred pattern on the wing-coverts. The last coverts to be moulted are the central greater coverts, replaced by mid-August. The new greater coverts may show a vermiculated, densely barred pattern.
The primary moult score for this bird is P7 fully grown, P10 old juvenile.