Herring
Gull - Zilvermeeuw (argentatus & argenteus): sub-adult March
(last update: 08 december 2003)
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Herring Gull sub-adult (argentatus), March 18 2003, Boulogne-sur-Mer, France (50.42N,1.34E).
This is large 4cy argentatus with almost all scapulars adult-like grey (except one rear lowest scapular), while the greater wing-coverts and the lower tertials are still obviously barred. Note also the extensive black on the bill, the clear winter streaking, small white tips on the outer primaries and the dark markings in the tail. The central median coverts, a few inner greater coverts and the two upper tertials have been moulted once more than the other coverts and appear more adult-like than the adjacent wing-coverts and the lower tertials, which have pale brown centres.
Last autumn sub-adult Herring Gull, so-called "third winter" birds (4cy by February) have replaced the all-brown immature primaries for more adult-like primaries, which show white tips when fresh, a grey basal half and often one or two mirrors (P9 and P10). A small minority doesn't show a mirror at all, as this bird shows. The size of the dark patches and the amount of black in the outer primaries is more extensive when compared to adults: there is often a broad dark sub-terminal band on P5 and a dark faint spot on the outer-web of P4. The dark patches are not sharply demarcated as in adult, but the dark outer-web gradually dissolves in the grey inner-web. Note the dark vermiculated markings on the tail-feathers in this individual.
In argenteus, from January to April, 4cy birds 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.
