Herring Gull - Zilvermeeuw (argentatus & argenteus): sub-adult August
(last update: 08 december 2003)
Herring Gull C03S0 4cy (argentatus), August 06 2002, Tampere, Finland (61.31N,23.43E).
A 4cy argentatus, ringed white C03S0 as pullus on June 15, 1999 in Vkoski, Finland. This bird is in active complete moult with the inner primaries moulted to fourth generation. Primary P7-P10 are still juvenile. The median coverts are fresh adult-like grey and the central greater coverts are dropped, showing the old third generation secondaries underneath. Most obvious immature features can be found in the lower tertials and the inner greater coverts. Note also the brown immature primary coverts.
From June to December, 4cy argentatus
undergo a complete moult resulting in so-called "fourth winter"
plumage. By August, the first
neat streaks can be found on the crown and hind-neck. After the complete moult is
finished by late autumn, the head will show extensive 'winter streaking', often
neat fine streaking in sub-adult argentatus.
During the summer, the primaries are moulted to fourth generation. The faded brown third generation primaries (with a mirror on P10) are replaced for true adult primaries. In argentatus, the last outer primary P10 will be fully grown by early December, slightly later than in West-European argenteus. First data from Tampere, Finland, indicate that 3cy argentatus from this region are not delayed in primary moult compared to argenteus.
Adult northern argentatus show a different
pattern in the outer primaries, compared to argenteus. In
argentatus, especially from northern Scandinavia, the black marking
on P5 is very limited and, if black on P5 is present, this black has
diffuse edges. But often, these black sub-terminal markings are completely
lacking on P5. In Baltic argentatus populations, black on P5 is confined
to the outer-web, with sharply defined edges.
The iris is clearly yellow in summer in most argentatus, but some sub-adult argentatus will keep the iris amber to dark brown.