Image: Joseph Kennedy, 15 August 2008 [larger view].
Nikon D200, Kowa 883 telescope TSN-PZ camera eyepiece 1/250s f/8.0 at 1000.0mm iso400.
Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:
After all of those big, mean-looking terns, it’s nice to see one as sweet and gentle as this little bird. How do we know it’s little? The pebbles and grass provide a welcome sense of scale, but even without them, the large eye, small bill, and generally “soft” aspect eliminate the larger species of tern.
The large terns, too, with the obvious exceptions of the long-billed noddies, Sooty, and Bridled, tend to appear white in the field, while our quiz bird gives a neat two-toned impression: dark gray above, white below and on the head, with some odd dark spots on the head. The tail falls far short of the folded wingtip on the perched bird. Small, dark-mantled, patchy-headed, short-tailed: this has to be a marsh tern, of the genus Chlidonias.
The marsh terns — Black, White-winged, and Whiskered — are obviously different from other terns. They feed like giant swallows, swooping low over the water to pick up insects and small fish, rarely or never diving from a hovering headstart like the large, “white” terns. Distinctive as they are as a group, they can be challenging to identify to species, especially in plumages other than the distinctive breeding feather of adults. A complication little regarded by many birders is the fact that American Black Terns (surinamensis) are different in appearance from Old World Blacks (niger), more closely resembling White-winged Tern in some ways.
The upperparts of our quiz bird are too dark for Whiskered Tern, which is larger, bulkier, and heavier-billed in any event. Our bird’s black auricular spot is relatively isolated on a very white head, connected (one assumes) to the invisible spot on the other “cheek” by a narrow, diffuse headband — a general pattern that is classic for White-winged Tern. Once I’ve got that idea in my brain, I start to see a short bill (Black Tern is longer-billed), and I can almost convince myself that there is a reddish tinge to the tarsus, which now strikes me as long. The flank and breast are white, without the gray wash conspicuous on some Black Terns, and I think that the pale rump contrasts with the slightly darker tail.
On the other hand, the upperparts are quite slaty, perhaps too dark for White-winged Tern, and the “corner” of the folded wing and the side of the neck both show dark, creating the “double patch” typical of Black Tern. And we need to remember that the head pattern of surinamensis Black Tern can approach that of White-winged.
If I saw this bird in the field, I’d look at it very closely indeed. Though most records are from the east coast, White-winged Tern is a good candidate for vagrancy anywhere in North America , especially in late summer. My suspicion is that the upperparts color and “double patch” make this, as expected, a Black Tern; but me, I’d go home with some question marks in my notebook — and hope to end the day perhaps a little more knowledgeable about terns, even unidentified terns, than I’d started it.
Review all mystery birds to date.