(2 images) Herring Gull BGAD 1cy (argenteus), November 28 1999, Westkapelle, the Netherlands (51.33N 03.25E). Pictures by Pim Wolf.

BGAD was ringed in a Belgian argenteus colony, ringed as pullus at Zeebrugge (51.21N 03.11E) on July 09 1999. It spend most of the winter near Westkapelle, photographed on two occasions. Showing typical 1cy argenteus features: the small pale crescents on the outer tips of the outer primaries and pale inner and outer-webs of the inner primaries, from P5 inwards. All upper scapulars and the upper lower scapulars have been replaced for second generation feathers. Note the moult in the under-parts: the head and upper breast are moulted to second generation feathers, somewhat colder brown-grey, while belly, flanks and vent still show the warmer brown juvenile 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.

photo above: BGAD 1cy, November 28 1999, Westkapelle, the Netherlands (51.33N-03.25E). Picture by Pim Wolf.

photo below: BGAD 2cy, February 06 2000, Westkapelle, the Netherlands (51.33N-03.25E). Picture by Pim Wolf.

BGAD, born in 1999 at Zeebrugge, now in 2cy. When comparing the two photo's, it's obvious not much changed between November and February. Moult in the winter months only continues at very low pace. As is the case with many so-called "first winter" argenteus Herring Gulls, the juvenile wing-coverts, tertials, remiges and rectrices appear more worn by February and the dark parts are slightly bleached. The upper scapulars and mantle were already replaced quite a while ago and the fringes of these second generation feathers start to wear as well; the white fringe has worn away. The anchor-shaped pattern contrast with the white outer-half. Note the abrasion in the tertials and the innermost wing-coverts: the fringes are reduced and the protruding shaft is obvious.