(2 images) Herring Gull ATAA1cy (argenteus), December 22 1999, Westkapelle, the Netherlands (51.33N-03.25E). Photo by Pim Wolf.

This is a rather dark argenteus, born and ringed as pullus at Zeebrugge, Belgium (51.21N 03.11E) on July 27 1999. Colour-ringed blue ATAA. Although rather dark, it still shows some characteristic features: 
- the notching on the tertials, although most of the white notching is worn away,
- the relative dark inner primaries, although typically showing a pale inner-web,
- the primaries are rather dark brown,
- the outer primaries still show a small white crescents on the tips,
- the outer greater coverts have a dark basal half.

photo below: ATAA2cy, February 18 2000, Westkapelle, the Netherlands (51.33N-03.25E). Photo by Pim Wolf.

A 2cy argenteus in so-called "first winter" plumage. 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. In February, the head and under-parts are still second generation, but the head and under-parts will turn much paler by June. The central lowest scapulars were moulted recently, 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.