Herring Gull - Zilvermeeuw (argentatus & argenteus): sub-adult December
(last update: 08 december 2003)
Herring Gull sub-adult, December 21 2001, Brouwersdam, the Netherlands (51.45N,03.51E).
The primaries show well-defined small white tip in this individual, clearly demarcated from the black area. P5 has the black sub-terminal marking confined to the outer web. The division between grey and black is sharply defined, unlike the gradual dissolving black found in many northern Scandinavian argentatus. This pattern is more in line with the argentatus from the Baltic region, but may apply to NW European argenteus as well. Note the obvious black bill markings, combined with the recently moulted all-grey outer primary coverts. It probably belongs to the Baltic race argentatus, as the upper-parts are rather neutral to dark grey and the black sub-terminal band would be broader and square, sometimes complete on both webs in argenteus.
From June to October, sub-adult Herring
Gull have a complete moult to so-called "adult winter" plumage.
As long as the old outer third generation primaries are visible (until
August), ageing as 4cy is rather straightforward. From November onwards,
4cy birds much resemble adult birds, except that the bare parts still show
immature features: the black bill-band is obvious, extending over both
upper and lower mandible. On average, this plumage develops a more
pronounced winter 'hood' than in full adults: dense streaking on head,
especially around the eye and in the hind-neck. The upper-parts,
wing-coverts and tertials appear adult-like grey from 4cy October onwards.
The fourth generation tail-feathers are plain white.