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QUIZ GULL #12 (with answer below)

Hints: no hints

ANSWER: The correct answer is Glaucous-winged x Western Gull hybrid.

This is a peculiar-looking guy. Aging this bird is rather easy. With the adult gray across most of the mantle (and some splashes on the median coverts and tertials) and lots of brown in the coverts and tertials, the bird is a second year bird. Moreover, it’s a second year bird with a four-year cycle. The mantle shade helps us rule out all the dark-mantled gulls (Western, Yellow-footed, nominate Heuglin’s, Lesser Black-backed, Kelp, Slaty-backed, Baltic, Great Black-backed). In fact, the bird is clearly too pale-mantled for Steppe (barabensis), Armenian, and taimyrensis Heuglin’s as well. The overall bulk of the bird (not to mention the extensive black in the bill) help us rule out Mew, Kamchatka, Common, Ring-billed, Black-tailed, and California. The black primaries enable us to rule out the pale-winged species: Glaucous-winged, Glaucous, Iceland, and Thayer’s.

The bird is heavily marked around the head and neck. That effectively rules out the “white-headed” guys (Yellow-legged, Caspian, and Mongolian—also Armenian and Steppe), which are quite white in the head in their second winter (and even in their first winter). The bill shape is interesting. It appears very thick, but beware it is slightly open, so appears extra thick. Nevertheless, there is a prominent gonydeal angle which is wrong for Herring and Vega.

All that leaves us with… nothing! Back to the drawing board. We might want to consider a hybrid possibility as well. The bill shape, overall bulk of the bird, short primary projection beyond the tail, visible white skirt of the secondaries, and rounded head with small dark eye are all classic Western and Glaucous-winged traits. Moreover, the solid smudging –almost horizontal barring- on the head and upper breast are unique to Glaucous-winged Gull (other species tend to have vertical streaking). The mantle shade is fine for Glaucous-winged as well—but the very dark (black) primaries are not; that’s a Western trait. Calling a bird a hybrid is never a sure thing, but this bird is a great candidate for a Glaucous-winged x Western hybrid, which are quite common on the west coast of the United States.

Glaucous-winged x Western Gull 12 (43% correct)
Western Gull 5
Herring Gull 2
Western x Herring Gull 2
California Gull 1
Vega Gull 1
Heermann's Gull 1
Glaucous-winged x Herring Gull 1
Scandanavian Herring Gull 1
Kelp Gull 1
Thayer's x Western Gull 1