Herring Gull - Zilvermeeuw (argentatus & argenteus): sub-adult January

(last update: 08 december 2003)

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Herring Gull sub-adult (argentatus), January 05 2002, Le Portel / Boulogne-sur-Mer, France (50.42N,1.34E).

In many respects this bird shows immature features, especially on wing-coverts, tertials, tail and bare part coloration. However, note the white tips on the primaries and the large mirror on the fourth generation outer primary P10. This combination of adult-like primary pattern and the immature outer rectrices still showing black markings and the rather smudgy brown-green coloured iris, indicate it is most probably a 4cy bird. But remember that some Scandinavian argentatus moult in a very slow pace and this bird might already be in its fifth calendar year.
In the scapulars, many feathers still have a brown hue. The last moulted feathers are grey based, see e.g. the recently replaced tertials which nevertheless still show a brown pattern on this grey base. In the central greater coverts a few similar grey feathers can be found, in the median coverts active moult is in progress in the outer coverts. 

From January to April, 4cy argentatus moult to so-called "third summer" plumage. By April, the head and under-parts will appear all-white. The tail-feathers, wing-coverts and primaries are not replaced, therefore most birds strongly resemble "third winter"  birds, although the white primary tips wear away and dark patches start to bleach. The iris is often yellowish, the orbital ring yellowish-orange and the bill predominantly yellow with a red gonydeal spot and limited black markings along the culmen by April.