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First off, a bit of housekeeping. Rule #1 for the ABA online photo quiz starts:
“An answer, consisting simply of the Common or English name exactly as it appears in the ABA Checklist ...”
Except in rare cases such as the two yellowlegs species, species names are singular, so even if there are three quiz birds of the same species, the correct answer should still be the species name. That is, if the subjects of a quiz were three Cory’s Shearwaters, the correct answer would be “Cory’s Shearwater.”
This week’s three quiz birds, due to the rules of the quiz, must represent a single species, so we can use all of them to solve the riddle. The waves behind the birds suggest that we’re on an ocean or a very large lake, a facet of the quiz that may be important. Or, it might not be. If it were an ocean, there is a number of species options that most of the ABA area’s birders do not know at all well, if at all, and many of us would need to haul down the various seabird references to figure it out. However, let’s first see if it’s something covered at least reasonably well in the regular field guides.
The obvious features that may help us to winnow the options include the dark-brown upperparts; wide-based, dark, square tail; and strong black-and-white barring on the uppertail coverts. These are features of a few species of gulls early in first-cycle plumage, particularly Mew, California, Herring, and Western gulls. However, all three birds have obviously initiated primary molt (all have new inner primaries; the darker ones at the trailing edge of the bend of the wing), thus they cannot be first-cycle gulls, as these dark species do not molt flight feathers in their first cycle. Any such gulls molting flight feathers would be older and sport at least some paler aspects to plumage on the upperparts, particularly head and rump).
Ruling gulls out may cause us to consider the true seabirds, members of the Procellariiformes. What few albatross options might be considered (Black-footed, Short-tailed [Steller’s]) are far too long-winged for our quiz birds. Additionally, the rump pattern rules out all of our petrel, shearwater, and storm-petrel options; the last group is also ruled out on numerous other aspects. These various excisions of possibilities leave us with just one group to consider, the skuas and jaegers, a group that hosts a number of the more difficult field-ID problems facing ABA-area birders. However, unlike our photographer, we’ve got a stable platform from which to ogle the birds, which are also kindly staying put. This should enable us to carefully scrutinize shape and structure, as well as the plumage characters presented by the multiplicity of individuals of whatever species they represent.
In addition to the active flight-feather molt, the right bird also shows a nearly all-dark underwing, another feature of older jaegers. The facts that these birds are not adults and not first-cycle birds make things a bit more tricky for us, unless we have ID references outside the standard ABA-area field guides. That is because such guides just do not have the space to cover the range of plumages inherent in species that take at least three years to reach definitive plumage, most of which also come in a variety of color types (not morphs, as there is ample evidence that suggests that juveniles of at least some of these species may change from dark to light as they mature to adults, though whether they can change from light to dark is unknown, at least to me).
With perusal of the bases of the primaries, we should be able to eliminate skuas from consideration, as there is just not enough white there for either of those species. Unfortunately, that leaves us with the three jaegers, rather than just the two skuas. While perhaps not definitive, the rump pattern argues against Parasitic Jaeger, as the pale bars on those feathers in that species tend both to buff or cinnamon and to not align into neat rows as on the two left quiz birds; this pattern is good for both Long-tailed and Pomarine jaegers. The upper bird provides the best image to assess the ratio of width of wing base to overall length (bill tip to tail tip), a ratio that can provide an excellent first approximation feature. The bases of the wings are quite broad, equaling about half the bird’s total length; both Parasitic and Long-tailed jaegers have considerably narrower wing bases. The quiz bird’s wings are also situated just about midway in the birds’ length (like a German or iron cross); the two smaller jaeger species usually show more length behind the wing than in front of it (like a Christian cross). Other features to note on individual birds include:
Left bird – no obvious projection of central rectrices and wide-based tail
Right bird -- the nearly all-dark wing linings indicate a near-adult (juveniles have heavily-barred wing linings); the strong side barring on the otherwise whitish belly, and the white bases to the underside primary coverts forming the “double white flash” typical of Pomarine Jaeger
Top bird -- no obvious projection of central rectrices, wide-based tail, and the yellowish bill with dark tip
Various of these features are supporting or definitive characters of Pomarine Jaeger. I took this picture of three subadult Pomarine Jaegers off San Diego, San Diego Co., CA, on 8 October 2011.
The following people (listed by submission date beginning with the earliest) submitted correct answers for the March Bird Photo Quiz—Pomarine Jaeger:
The following list shows the number of submissions for each species guessed.
The photo and answer for this quiz were supplied by Tony Leukering.