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What an interesting view! This month's quiz bird has a fairly long neck; long, thin, and pointed wings; and a very short tail with the bird's feet extending well beyond the tail's tip. These features allow quick elimination of most bird species and should head us toward two groups, the loons and the grebes. Other waterbird groups have members with short tails, but most of those also have short necks (e.g., tubenoses). The overall plumage pattern eliminates the two smallest grebe species. All other grebe species are ruled out by our bird's lack of any white secondaries. Additionally, Red-necked Grebe would not be quite this starkly white-and-black below and neither Western Grebe nor Clark's Grebe sports anything like this bird's neck pattern, so on to the loons.
Once among the Gaviidae, our eyes might quickly latch onto the vent strap – a thin, but obvious, dark line crossing the body between the feet. This is a feature well-known in separating Arctic from Pacific loons, with presence indicating Pacific. (A quick aside: vent straps are useful in some other groups, such as the Solitary Vireos and the Black-throated Green Warbler complex.)
Well, that was easy!
Not so fast. Just because an individual bird sports a feature that separates two similar species of a group (such as the aforementioned Pacific and Arctic loons), does not mean that is provides an identity character that rules out all other species. This is a point that lures many a birder down the primrose ID path! Yes, our quiz bird has a vent strap, but let's check to see that the bird actually falls in the Pacific/Arctic camp rather than elsewhere among the loons. The first feature that we might check as confirmatory is the neck pattern. Our bird does exhibit what might be termed a chin strap, but that chunk of dark on the neck is much too wide and obvious for the chin strap of a Pacific Loon. Additionally, that patch of dark is too low on the neck; the chin is higher on the neck, about where the width of the head narrows at the base. Adults of both Pacific and Arctic loons in basic plumage don't show any such dark patch on the neck, but juveniles can be heavily marked here. However, in those heavily-marked juveniles, at least of Pacific Loon, the dark coloration on the neck extends farther up the neck toward the head (as in http://www.flickr.com/photos/tony_leukering/1994650566/in/set-72157603872602322/).
Having to decide among the other three of the world's five loon species, we might let our eyes travel past the vent strap to the bird's feet. Seeing them, one might think of Little Red Riding Hood: "My, what big feet you have!" They are big – and a very useful feature in flying-loon ID. The two medium-sized loons (Arctic and Pacific) have intermediate-sized feet and can confuse the issue, but we've already ruled those two species out. Thus, with such huge feet, we can also rule out Red-throated. Of course, we could have ruled that one out on the same neck-pattern features for which we ruled out both adult and juvenile Pacific (and Arctic) loons, but I thought that I'd take the opportunity to stress the usefulness of foot size in identifying flying loons. There, is that enough emphasis?
We are left with the two large loon species, at which point, the identification should become fairly automatic. Yellow-billed Loon is never, in basic plumage (!), as dark on the head and neck as is our quiz bird. I took this picture of a Common Loon flying over the Seawatch site (http://www.njaudubon.org/SectionCapeMayBirdObservatory/MigrationMonitoringProjects/Seawatch.aspx) at Avalon, Cape May Co., NJ, on 2 November 2008.
The following people (listed by submission date beginning with the earliest) submitted correct answers for the December Bird Photo Quiz—Common Loon:
The following list shows the number of submissions for each species guessed.
The photo and answer for this quiz were supplied by Tony Leukering.