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QUIZ GULL #9 (with answer below)
The correct answer is L. heuglini heuglini/taimyrensis, "Taimyr Gull", the eastern form of Heuglin's Gull, often considered part of the Asian Herring/Lesser Black-backed Gull complex. More technically correct, Hong Kong birders have pointed out that the quiz bird is actually a taimyrensis x birulai (vega) intergrade, which regularly occur among wintering gull flocks in Choshi, Japan. This is a tough one, so we'll give full credit for either answer!
We see first and foremost that we have an adult gull this time. The yellow bill with red gonydeal spot and no black mark is enough to rule out Mew, Common, Kamchatka, Black-tailed, Ring-billed, Armenian, and Steppe (barabensis) (California very rarely lacks black in the bill). The shape of the bill is rather straight, lacking much of a gonydeal bulge, casting doubt that this bird could be a Western or Yellow-footed. Also, those species nearly always show a white skirt formed by the exposed secondary tips, which this bird does not show. The black in the primaries eliminate Iceland, Glaucous, and Glaucous-winged.
The mantle color is fairly dark (though the photo seems a tad underexposed). Nevertheless, we can rule out all the paler-mantled gulls: Herring (argenteus, smithsonianus, and argentatus), Thayer's, Caspian (cachinanns and ponticus), and even Yellow-legged (michahellis) and California. We can also rule out the very dark-mantled gulls: Lesser Black-backed (intermedius only), Baltic (that, is L. fuscus), Great Black-backed, and Kelp. That leaves us with Mongolian (mongolicus), Vega, Yellow-legged (atlantis), Heuglin's (antelius and heuglini/taimyrensis), Lesser Black-backed (graellsii), and Slaty-backed. The bird still seems a little dark for the first three and a bit light for Slaty-backed and graellsii, but we'll keep them in.
Now we have to focus on whatever clues we can find. The hint states that the eye may be pale, so we can't really do anything with that. The pattern on P10, visible on the underside of the left wing, is intriguing. It shows a small to medium-sized mirror, separated from the white tip by a black band that is quite thick, about the same width as the mirror. This is said to be a trademark of Heuglin's Gull. The more usual pattern for most gulls is a large mirror on P10 separated from the tip by a thin black band, which fits all the other remaining candidates (though I wonder about graellsii; check out the heuglini-like P10 on a Texas bird at Martin Reid's site).
Finally, let's get to leg color. Orange?! Kennerley et al. (Hong Kong Bird Report 1994: 127-156, Dec. 1995) report that, for mongolicus, "Leg color in particular is extremely variable, and ranges through orange, yellow, and pink." He also notes that, for taimyrensis, "The legs are usually washed yellow and are not particularly bright but can occaisionally be bright orange-yellow." To my knowledge, these are the only large gull forms for which orange is reported as a regularly occurring leg color.
Now, why is this bird an intergrade with birulai and not a pure taimyrensis? The legs are not orange-yellow enough (note there is a still a distinct pink tone to the legs) and the mantle is not dark enough. Also, the dark eye (assuming it is dark) fits pure vegae better than pure taimyrensis. One final note: the mirror on the underside of P10 is small enough that it suggests a 4th year bird.
This bird was photographed in March, 1999, in Japan by Wataru Kojima, copyright 1999. He reports that this bird was "typical" of the "taimyrensis" occurring in Japan, though it is not typical of the more pure taimyrensis that winter in Hong Kong.
This was clearly the toughest one so far, and the answers were all over the map. Pretty interesting given it's a profile of an adult gull. One person nailed the answer perfectly, stating the bird looked like "something to the east of pure taimyrensis".
|GUESS||# OF VOTES|
|Heuglin's Gull||5 (1 guessing hybrid) (20% correct)|
|Yellow-legged Gull (michahellis or atlantis)||6|
|Lesser Black-backed Gull||4|
|Caspian Gull (cachinaans)||1|
|Herring x Yellow-legged Gull||1|
|Steppe Gull (barabensis)||1|