Herring Gull - Zilvermeeuw (argentatus & argenteus)
(last update: 08 december 2003)
Herring Gull adult (argenteus), May 12 2001, Westkapelle, the Netherlands (51.33N-03.25E). Picture by Pim Wolf.
By mid-May the inner primaries are shed, although this individual still has all 10 primaries unshed. The pattern on the outer primaries is typical for argenteus with black on P5, which may vary from a full sub-terminal band to black on the outer-web on argenteus. There is a round mirror on P9, which is confined to the inner-web. On P10, the mirror merged with the white tip at the centre, with the black sub-terminal band limited as triangular spots on the edges of the inner and outer-web. The black patch between the apical spot and the white inner-web (the medial band) is very broad along the edge of the inner-web on P10. Argenteus normally shows such a broad medial band, where it is restricted in argentatus. Note also the diffuse division line between the grey centre and the black outer-web of P9 (and also P10). Such a diffuse division, with much irregularities ("saw-blade motive") can be found commonly in Herring Gull, where e.g. cachinnans often shows a neat clear division between the black outer-web and the whitish centre.
Argenteus has a partial moult of body and head in spring. It starts in January (when adults in the Netherlands may already return to the colonies) and is completed by April, leaving birds in so-called "adult summer" plumage. The head is clean white and the white primary tips are slightly worn and the dark patches bleached. Otherwise, this plumage much resembles the "adult winter" plumage. The bare parts are more saturated, as the breeding season has started.
From June (often mid-May in Belgium and
the Netherlands) to October, a complete moult will bring birds in
so-called "adult winter" plumage. A new set of primaries will
grow during the summer months and by mid May, the first, innermost primary
will be dropped in argenteus in the Netherlands.