QUIZ GULL #2: what is this (down to subspecies level)?
ANSWER BELOW

ANSWER:

The correct answer to Gull Quiz #2 is adult Scandanavian Herring Gull, Larus argentatus argentatus OR the Herring Gull of NW Europe, L. a. argenteus.

The very pale undersides of the primaries and secondaries help rule out any dark-mantled species. The black on the primary tips rule out the pale species (Glaucous, Iceland, Glaucous-winged). The key mark, however, is the terminal mirror on P10, as well as a medium sized mirror on P9. These are typically only found on Great Black-backed Gull, nominate cachinaans Yellow-legged Gull, and nominate argentatus Herring Gull. They are also found occasionally on argenteus. Great Black-backed is ruled out by the pale undersides of the flight feathers. Cachinaans can probably be ruled out by the lack of a thin pale tongue on P10, by the tiny black band on P5 (and most cach. have black on P4 as well), and by the bill shape (cach. should appear more thin and pointed). Thayer's and Kumlien's also have dark marks on the outer primaries and a terminal mirror on P10, but on Kumlien's the black is more gray, and on both the black areas are far more restricted than on this bird.

The extensive black on the outer primaries visible from below, as well as the very pale undersides, lean toward argenteus. The faint, almost absent, black band on P5 points toward argentatus. So does the location. This bird was photographed by Juha Niemi on April 1, 1994 in Finland (copyright 1998).