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QUIZ GULL #8 (with answer)


Hint: no hints

ANSWER:

The correct answer to Quiz Gull #8 is juvenile Baltic Gull, Larus fuscus with partial credit for "Lesser Black-backed Gull". Here's my reasoning:

At least we get to see the whole bird this time. Aging it is not so tough: it's clearly a young juvenile by the dark bill combined with fresh dark upperpart feathers with crisp white edges. (Though some species, such as graellsii and Glaucous-winged, can keep a black bill even into second winter). Note that all of the feathers appear fresh and of the same age; no worn edges. Even the folded primaries show fresh tips. The nearly black primaries rule out, at least, Glaucous, Glaucous-winged, Iceland, and Thayer's.

Perhaps the first obvious feature of this bird is its rather petite appearance and rather thin bill. Clearly, this is no Great Black-backed, Western, Yellow-footed, or Kelp Gull. The other thing to consider is the rather whitish head and underparts (the breast appears quite pale). By first winter, it's going to be quite white. It seems too white, especially in fresh juvenile plumage, for smithsonianus Herring Gull (plus, the striking mantle and scapular feathers lack the "holly-leaf" shape that is seen on most forms of juvenile Herring Gull) or California Gull (which can have a black bill in juvenile plumage). In fact, lets narrow the field to those gulls that can have juvenile plumages most similar to this: a fairly white head and underparts. That would put us squarely in Europe and Asia: fuscus, graellsii and intermedius, michahellis, cachinnans, possibly barabensis and mongolicus, heuglini and taimyrensis, and armenicus. Now let's focus on the thin bill. It's delicate enough to have serious doubts about michahellis and armenicus, both of which also have a steeper curve of the culmen to the tip and shorter wings than this bird. Next, let's focus on the greater coverts. The solid area at the base of the outer greater coverts is not good for heuglini/taimyrensis (which also has a paler tone to the upperparts, contrasting with the primaries) and mongolicus (which has more heavily streaked underparts and usually more patterned tertials as well). Like heuglini/taimyrensis, on juvenile cachinnans the general tone of the upperparts is much paler, so that there is obvious contrast with the nearly black primaries. They also appear more long-legged.

We're now down to the Lesser Black-backed group of fuscus (now often separated out as Baltic Gull), graellsii, and intermedius. I suppose partial credit should be given for any of these, but the short legs and long primaries, extending well past the tail, are a trademark of fuscus. Also, the overall delicate look and thin bill fit this species as well. Rik Winters writes: "I was struck by the headshape of the birds (fuscus): the highest point of the crown was at the end of a quite steep forehead, and clearly behind the eye, a feature at best uncommonly shown by LBBG (graellsii or intermedius). The ID of every bird I tested on this feature since, was in accordance with this presumed difference, like your mystery gull! In fact, this was the only reason I was quite sure it had to be fuscus!" Pale underwings is also a good way to separate fuscus, but that, of course, is not visible here. This juvenile Baltic Gull was photographed August 25, 1999 in Finland by Janne Kilpimaa (copyright 1999) and may be viewed at his website under "kuva23". Special thanks to Martin Reid in helping me figure out how to rule out all the contenders.

This quiz proved one of the easier ones, and generated lots of answers, with the majority nailing the partial credit answer of Lesser Black-backed Gull. Only a few went on to guess Baltic Gull, however. Here are the results:

GUESS # OF VOTES
Baltic Gull 3 (13% correct)
Lesser Black-backed Gull 13 (54% for partial credit)
Kelp Gull 1
Herring Gull 1
Thayer's Gull 3
California Gull 1
Yellow-legged Gull 2