Monday, January 10, 2011

Quiz #381 (2011-1-02) Solution

Click on picture(s) for a larger view.

Answer by Tony Leukering

First off, I gave an extra bonus point to all those providing a correct answer for the white-headed shorebird in the background that was supposed to have been cropped out of the quiz picture; it is a Sanderling, and no one got that species wrong that provided a species name for it (others were not penalized). Secondly, I was expecting that respondents would have trouble with the Pluvialis plovers -- they can be truly difficult, but was a bit surprised by the difficulty that respondents had with the four yellow-legged sandpipers.

With both sets of focal species proving a bit tricky, where to start is critical, as each species can inform on the other, particularly with size comparison. So, as the bird exhibits a very distinctive feature, I'll start with the top right of the four sandpipers. These four are dumpy and have short yellow legs (note the emphasis on the first modifier), a medium-length bill, and little in the way of plumage distinction (being brownish-gray above and whitish below), except for one key feature. That feature is the distinctive pattern to most of that upper right sandpiper's upperparts feathers: solid brown except for a thin white fringe and a dark subterminal band (one does need to enlarge the pic to be sure of the pattern). Only two ABA-area shorebird species sport this pattern, one of them being Temminck's Stint. Though bill length and/or leg length can rule out all the species incorrectly provided by respondents, these distinctive feathers do an even better job of ruling them out, as they are juvenal feathers of Red Knot. Temminck's Stint is ruled out by the birds' size; any Pluvialis would dwarf Temminck's Stint. Once we know that the sandpipers are Red Knots, all the shape features line up quite nicely: both bill and legs are too short for Stilt Sandpiper, the legs are too short for either Pectoral or Sharp-tailed sandpipers, and the birds are too large for Least Sandpiper.

With the plovers, it is key that they are all the same size, or virtually so, suggesting that they are all either Black-bellied Plovers or some combo of golden-plovers, not both. The picture is over-exposed (and I purposefully left it that way), so we might be a little wary of the color of the spangling on the upperparts, as golden spots might have been "blown out" by the overexposure, so the more "golden" species (European and Pacific) are not immediately ruled out by what appear to be whitish spangling. I will start with the front left bird. It is mostly brown with whitish spangling above, but it has a number of black-and-white feathers; these must be remnants of alternate plumage, thus the bird must be an adult. At least four other of the plovers show at least some trace of alternate plumage. Others, however, appear to be sporting at least some juvenal plumage. This combo of ages with the adults nearly out of alternate plumage suggest that the picture was taken later in fall, perhaps October or November. A number of the birds exhibit very long primary projection, while a couple show either shorter projection or are indeterminant. Thus, if these are golden-plovers, they have to be Americans or a mix of American and Pacific. However, Black-bellied, too, has very long primary projection, so that species is still in the hunt.

Bill size and shape is one of the better features allowing separation of Black-bellied from the various golden-plover species, but I find that it's often difficult to use in isolation, that is, with only one species present. To me, the bills look quite long and relatively thick, but I need not rely on that feature, because there are still a couple of very useful plumage bits that are very good species determinants. The bellies on all the plovers on which we can see them appear whitish (American and Pacific golden-plovers are grayish), while the crowns on most of them are pale and do not contrast darker than the rest of the head (as in all golden-plovers), except for the bird in the center holding the most alternate plumage and the bird in the back facing right. That back bird might, indeed, be a good candidate for a golden-plover, as it seems warmer, but that could be the angle in which the bird is standing relative to that of all the others. However, looking at head shape, we can see that it's head appears to be deeper from front to back than it is tall, while golden-plover heads are roughly the same dimensions front to back and top to bottom. Finally, Red Knots are of about the same size as the various golden-plovers, but are noticeably smaller than are Black-bellied Plovers.

Incorrect species provided as answers:
Least Sandpiper - 2
Sharp-tailed Sandpiper - 1
Pacific Golden-Plover - 4
Pectoral Sandpiper - 3
American Golden-Plover - 5
Stilt Sandpiper - 1
Rock Sandpiper - 1
Ruddy Turnstone - 1
Purple Sandpiper - 1

Congratulations to the 11 of 23 getting the quiz correct:
Ben Coulter
Christian Nunes
Al Guarente
Peter Wilkinson
Adrian Hinkle
Pam Myers
Christopher Hinkle
Tucker Lutter
Matt Bristol
Chishun Kwong
Joel Such

Answer: Black-bellied Plover, Red Knot (and Sanderling)