Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 6-2-2007)

Herring Gull H-1172113cy (argenteus), December 14 2003, Westkapelle, the Netherlands (51.33N 03.25E). 

This Belgium 3cy argenteus was ringed as pullus on July 09 2001 Zeebrugge (51.20N 03.11E).

From June to October, a complete moult will bring 3cy argenteus in so-called "third winter" plumage. From October onwards, when the complete moult is finished, the head shows extensive 'winter streaking', mottled brown contrasting with the white breast as in some birds (as an executioner's hood). The scapulars and mantle are pale adult-like grey, although a few feathers may reveal the 3cy age-class and have a brown pattern near the tip.
By the end of the complete moult (October), all wing-coverts have been replaced, most to plain grey feathers in typical argenteus. But it's very common to find immature patterns on the wing-coverts and tertials, often be found in the lower tertials, greater coverts and outer lesser coverts (the carpal edge).
By November, all primaries have been replaced for third generation flight feathers. The first inner primaries were dropped by late May and the outer primary P10 was dropped by late August. The primary moult is completed by late-October in argenteus, when the new outer primary P10 is fully grown. Argentatus, especially from the far northern populations, may show a delayed primary moult timing. 
The third generation inner primaries are clearly adult-like, with the 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. 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 third generation tail-feathers are white, with various clear immature black markings. The iris is pale brown-yellow, but may turn darker in winter, especially in nominate argentatus from the Baltic states.