Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 6-2-2007)

(3 images) Herring Gull 3cy 4272754 (argentatus), September 21 2004, Scheveningen, the Netherlands.

A bird with a Helgoland ring: 4272754; darker grey than local argenteus (compare with adult in the foreground). Primary moult score: P7 fully grown, P8 at the length of P6. P5 has a complete sub-terminal band and there are dark markings on the outer-web of P4 (bottom image). Many central greater and inner median coverts show an obvious barred pattern, while later moulted feathers as the upper lesser coverts appear more uniform grey (although some show a brown hue). The head feathers have been replaced by extensively brown mottled feathers. Note the amber iris and immature bill.

From June to October, a complete moult will bring 3cy argenteus in so-called "third winter" plumage. By September, when the complete moult is (almost) finished, the head will show extensive 'winter streaking', mottled brown contrasting with the white breast as in an executioner's hood. The scapulars and mantle are pale adult-like grey, although some individuals may show an immature pale brown hue on the lower scapulars. 
By the end of the complete moult (October), all wing-coverts have been replaced, most to plain grey feathers. Immature patterns can often be found in the lower tertials, greater coverts and outer lesser coverts (the carpal edge).
During the 3cy summer, the primaries are 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 in argenteus, when the new outer primary P10 is fully grown. The table below shows some September data from Scheveningen harbour. 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. The white primary tips are obvious in the inner primaries, but only poor developed 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 turns pale yellow in summer (from July onwards).