Herring
Gull - Zilvermeeuw (argentatus & argenteus): sub-adult March
(last update: 08 december 2003)
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Herring Gull 4cy (argenteus), March 17 2003, Boulogne-sur-Mer, France (50.42N,1.34E).
This is clearly a sub-adult with the scapulars completely adult-like grey
while the wing-coverts and the tertials show some barred feathers. Note
also the brown hue on the greater primary coverts, the greenish hue on the
iris and the extensive black on the bill.
Last autumn, 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.
From January to April, 4cy argenteus 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.
