Saturday, 29 December 2012

Herring Gull (Larus argentatus): smithsonianus look-alike type

This 3rd winter Herring Gull (Larus argentatus) was seen just west of Bønnerup Harbour on the north coast of Djursland in Denmark on December 28, 2012.

The uniform brown 'sjawl' and the pattern of the tail-coverts; traces of brown and black in the wing coverts and tertials; distinct primary pattern with broad black band on P5 and white mirror on P10; and the tail band in this bird gave a smithsonianus impression.

3rd-cycle is a very tricky plumage and it is thus vital to look at the whole plumage with a critical eye. Details like the tail and secondary pattern are crucial, and unfortunately do not look typical for smithsonianus in this one.

Note that the dark in the tertials is blackish as in smitsonianus rather than brown as often is the case in typical Herring Gull

The new (grey) mantle feathers are slightly paler than on the nearby argentatus which was also the impression when it was seen together with other adult and near-adult argentatus

Densly dark-patterned hindneck, creating solid dark necklace

Note extensive blackish-brown in tertials, only with vermiculation at the tip

Barred undertail coverts. Thin barring on the tail coverts in a 3rd-cycle Herring Gulls indicate a northern origine such as Iceland

The hindneck shows rather plain and smooth streaking (usually a lot of longitudinal streaking in typical argentatus)

Scattered smudging across breast from nape ...

... and dark smudging on the belly

New innner primaries strickingly paler than greater coverts as in smitsonianus and argenteus, but more rare in argentatus. Note also white mirror on P10

The black mark on P6 seems to have a sharp point (or 'bayonet') extending up the outer edge of the feather. Note also what appears to be a sharply pointed black 'W' mark on P5 and the white tips to the grey inner 'tongues' (or wedges) on the inner webs of P6 and P5. These features are typical of American Herring Gull

The secondaries are irregularly vermiculated brownish as in European Herring Gull and lack clean black as in smithsonianus

Note discrete dark brown marks on secondaries. The greater coverts of 3rd winter smithsonianus are not usually this coarsely barred, and the same is true for the tertials

Note that tail is still rather heavily marked, however, in smithsonianus the tail usually looks a bit more solid black than this

Sooty tipped underwing coverts and white armpits

Note that there are a few barred uppertail coverts