(5 images) Herring Gull 5.363.361 2cy (argenteus), February 2002 & November 2003, IJmuiden, the Netherlands (52.27N-04.33E).
A 2cy argenteus in so-called "first winter" plumage, ringed in the Netherlands: Arnhem Ringstation 5.363.361. It was ringed as weakened 1cy on September 06 2001 at IJmuiden and it was held in captivity for more than 24 hours.
Argenteus has a partial moult of head and body-feathers in spring. This partial moult starts in January and ends by May, leaving birds in so-called "first summer" plumage. The head and under-parts resemble the pattern in 1cy birds, although the head and breast turn much paler by June. The lowest scapulars may still be moulted in this period, showing a buffish tone and a neat pale fringe. The adjacent juvenile rear lowest scapulars are very worn by February.
The juvenile tertials, lesser, lower lesser and median coverts have a notched pattern, strongly worn by February. The juvenile greater coverts show a 'piano-key' pattern; in argenteus on the outer greater coverts as well. The juvenile tertials have an obvious notched pale fringe and transversal bar.
The juvenile wing-coverts, rectrices and remiges are bleached and show wear in the fringes. 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.
Normally argenteus shows much more wear in the coverts, tertials and scapulars than Scandinavian argentatus. Furthermore, argenteus has an on average higher moult score in the scapulars, with quite some argentatus still show many juvenile scapulars. Differences in moult score in other feather tracts is not expected; both argentatus and argenteus retain their juvenile wing-coverts, remiges and rectrices well into spring.
2 images below: Herring Gull 5.363.361 2cy, February 04 2002, IJmuiden.
2 images below: Herring Gull 5.363.361 3cy, January 23 2003, IJmuiden.
3 images below: Herring Gull 5.363.361 3cy, November 08 2003, IJmuiden.
From June to October, a complete moult will bring 3cy argenteus in so-called "third winter" plumage. By November, when the complete moult is finished, the head and breast show extensive 'winter streaking', mottled brown contrasting with the white breast. The scapulars and mantle are pale adult-like grey, but a few immature feathers are often still visible, showing an anchor pattern.
By the end of the complete moult, all wing-coverts have been replaced, most to plain grey feathers although there may be diffuse patterns. Such immature patterns can often be found in the lower tertials, greater coverts and outer lesser coverts (the carpal edge).
During the summer, the primaries were moulted to third generation. The first inner primaries are dropped by late May and the outer primary P10 will be dropped by late August. The primary moult is completed by late-October or November in argenteus, when the new outer primary P10 is fully grown. The third generation primaries are clearly adult-like, with the inner primaries P1-P4 plain grey with a white tip. The outer-wing shows a clear black triangle, extending on the greater primary coverts. From P4 outwards, the primaries show a black sub-terminal band in many birds, but this individual has black on P5-P10. The white primary tips are obvious in the inner primaries, but often smaller on P9 and P10. P10 has a small white mirror (lacking in some birds). The new tail-feathers will be white, with clear immature black markings. The iris is pale brown-yellow.