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When all else fails, put up a picture of a gull!
For photo quizzes, that little adage works amazingly well, because a large percentage of birders do not know gulls well, do not like gulls, do not study gulls. As can be seen from the list of species provided as answers this month (below), even good pictures of gulls can provide problems. We can see our quiz bird's head well, colors are readily assessed correctly, and most of the relevant field marks are visible on the bird. If only we had a known species to provide a size comparison. Ah, there's always something missing in a quiz picture! But, look at the bright side, the ABA online quiz does not allow for hybrids, so we don't have to worry about that huge bucket of ugliness!
As with many birds, but particularly with gulls, it is very helpful to age the bird when starting down the ID road. However, I might first determine whether our bird is a smaller gull or a larger gull. With such a dark mantle, if our bird is not either a Laughing Gull or a Franklin's Gull, then it cannot be a small gull. The dull pink legs rule out both of those options. Those legs also rule out typical members of Red-legged Kittiwake, one of the larger smaller gulls and darker-mantled than Black-legged Kittiwake, but still really too pale-mantled for our quiz bird. The leg color paired with the bill color and pattern rules out Black-tailed Gull. Thus, it looks like our quiz bird is among that quite-difficult and taxonomically-uncertain group of beasts known as "large, white-headed gulls." With the bird's dark mantle, the options are Western, Yellow-footed, Lesser Black-backed, Slaty-backed, Great Black-backed, and Kelp gulls.
With our choices already whittled down to six possibilities, we'll go back to ageing our beastie. It seems to have very little brown in the plumage, but the white tail still sports black corners. These two items suggest that we're looking at a subadult, and an older subadult at that. All of our options except Yellow-footed are four-year gulls (that is, they typically achieve adult or definitive plumage in their fourth calendar year). Such birds usually sport more brown plumage and have more black on the bill in their second year, so our bird is looking good for a third-year gull. Unless it's a Yellow-footed Gull, in which case it would be a second-year gull.
Now, a quick digression on skirts (for an explanation of the term, see Quiz # 335 on the CFO online quiz [http://cfo-link.blogspot.com/2010/02/current-mystery-quiz-335-2010-1-06.html]). A skirt is somewhat indicated on our quiz bird, as we can see the tips of some of the secondaries and, boy, do they look worn. As the presence of a skirt would cut the number of options by two (the two "black-backed" gulls), it would behoove us to determine if this possibility is reality. Though the tips of the secondaries are worn and would protrude even farther if they weren't, our bird is also, apparently, in the midst of some posture change, as the two wings are elevated and the right wing is just slightly extended. Additionally, all the mantle feathers, tertials, and some scapulars and wing coverts are at least somewhat elevated. Thus, the appearance of a skirt could be due to this shift. Or not. I'm not sure that I'd be comfortable basing the ID on a skirt that may or may not represent reality.
Now, let's go back to leg color. Most large white-headed gulls with adult color to mantle and wings sport adult leg color. So, if that's true, we should be able to eliminate half our options: Yellow-footed, Lesser Black-backed, and Kelp. The dullness of the pink also makes a strong argument against Western and Slaty-backed. Wow, that seemed too easy. Is it really a Great Black-backed Gull? We should confirm that tentative ID with more characters and the more, the better.
For the next bit, it is important to understand that, on average within species, males have bigger and blockier heads with more sloping foreheads and larger and deeper-based bills than do females. As our bird's forehead is fairly slopy (is that a word?), it might very well be a male. However, males of five of the six species we've been considering have very substantial bills and our bird's bill just does not strike me as substantial. Additionally, our bird looks to have a fairly large eye, relative to its head size and that eye seems placed far forward relative to the gape. In many of the largest species of gulls, most of which are in our possible solution set, the eyes are small and fairly beady-looking on those big, blocky heads. While I haven't discerned whether the placement of the eye relative to the gape is something that works consistently, those two facets of eye (size and placement) give Lesser Black-backed Gull a different look than most of the other species we've been considering.
"But, what about the leg color," you might ask. Unlike most all of the other dark-mantled gulls, Lesser Black-backed Gull is prone to retaining pink legs deep into its development to being an adult. In fact, a small percentage retain pink legs (or mostly pink legs) into adulthood. Of all of the third-cycle Lesser Black-backed Gulls I've seen (all in the New World), more than half have had entirely pink legs. Our bird just might have started changing leg color, as the bit of leg visible above the "ankle" looks a bit yellowish to my eye and on my screen. Additionally, the species seems to me to also be relatively slow in plumage and bill-color change, too. This one, however, has much less black on the bill than nearly all third-cycle LessBacks that I've seen and more adult-type wing color than I usually see on that age. Hmm, perhaps it's a fourth-cycle bird. These things just stymie at times!
This Lesser Black-backed Gull in the later stages of its prebasic molt (of whatever cycle it's in, 3rd or 4th) was on the beach at the Cape May Migratory Bird Refuge, Cape May Co., NJ, on 29 August 2009.
The following people (listed by submission date beginning with the earliest) submitted correct answers for the April Bird Photo Quiz—Lesser Black-backed Gull:
The following list shows the number of submissions for each species guessed.
The photo and answer for this quiz were supplied by Tony Leukering.