Herring Gull 2cy (argentatus), February 09 2003, Boulogne/Mer, France (50.43N-01.37E).

A strong and powerful bird, with a sloping forehead "snout", the long primaries, creating an elongated rear end when perched and the strong, powerful impression. Some argentatus have the tail pattern limited, resembling Great Black-backed Gull (L. marinus) in pattern. This individual has most scapulars moulted for second generation feathers (upper scapulars: 75-100% moulted, lower scapulars 25-50% moulted, total: class 50-75% moulted). The moulted scapulars show a pale base and an anchor pattern on the tip. Note the moult stage in the under-parts and the head, with the head and upper-breast moulted to second generation feathers. Argentatus on average has a delay in moult compared to argenteus by February, especially the argentatus populations from northern Scandinavia. Furthermore, argentatus may show wing-coverts in much better condition, as this bird shows, still with the neat white fringes in the median coverts and on the greater coverts. In argenteus, the wing-coverts may look neat as well, but the white fringes of the feathers are almost always gone by February. Typically, argentatus can show very contrasting patterns on the inner primaries, making the window in the spread wing very obvious.
The partial autumn moult in NW European 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 with a pale base in some individuals, sometimes with a paler base, and the legs are flesh-pink.