Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 7-3-2007)

(2 images) Herring Gull 3cy (argentatus), July 15 2003, Tampere, Finland (61.31N, 23.43E).

A 3cy argentatus, together with an adult yellow-legged Baltic argentatus. P8-P10 are still old second generation, P1-P5 are fully grown, but P6 almost equals P5. The bottom image shows the secondaries and pattern on the fresh third generation primaries. Most scapulars and recently replaced median and greater coverts are grey. The earlier moulted scapulars show a brown hue, and the earlier moulted inner median and inner greater coverts have a brown base with narrow black lines.

From June to October, a complete moult will bring 3cy argentatus in so-called "third winter" plumage. By August, the first neat streaks can be found on the crown and neck. After the complete moult is finished in autumn, the head will show extensive 'winter streaking', often neat fine streaking in argentatus and mottled brown contrasting with the white breast as in an executioner's hood in many argenteus. The scapulars and mantle are pale adult-like grey, although some individuals may show an immature pale brown hue or arrow-head patterns on the lower scapulars. 
By June, 3cy argentatus are moulting new third generation plain grey wing-coverts, starting with the outermost median coverts. Contrary many argenteus, 3cy argentatus often show immature patterns on the inner greater coverts, inner and outermost median coverts and upper tertials (the first moulted wing-coverts and tertials in the complete summer moult). When inner greater coverts and median coverts were included in the partial autumn moult in 2cy, these feathers are left out of the moult sequence in the very early moult-stage. By the end of the complete moult (October), all wing-coverts have been replaced.

During the summer, the primaries are moulted to third generation. In argenteus, 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. Preliminary data from Tampere, Finland, indicate 3cy argentatus from this region are not delayed in primary moult compared to argenteus from continental NW Europe. The third generation primaries are clearly adult-like, with inner primaries P1-P3 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 black sub-terminal markings. The white primary tips are obvious in the inner primaries, but are only poor developed on third generation P9 and P10. The third generation P10 normally shows a small white mirror (lacking in some birds). The new tail-feathers will be predominantly white, with clear immature black markings. The iris turns pale yellow in summer in most argenteus (July-August), but quite some argentatus will keep the iris amber to dark brown.

In the tables below, the primary moult scores of 3cy July argentatus in Finland can be read: