Friday, August 7, 2015

Fri-D: White-rumped Sandpiper, and Some Shorebird Generalities

[You can click to enlarge this photo.]

Fall (southbound) migration of shorebirds has been underway since late June, and will be peaking soon.  Today at the South Cape May Meadows, NJ, I encountered the first juvenile shorebirds I have seen this year, in the form of two Lesser Yellowlegs with the nice fresh plumage and sharply defined white spots above characteristic of juveniles of that species. In shorebirds, adults tend to migrate south before juveniles; in the mid-Atlantic, July is the month of adult shorebirds, while August and September feature both adults and juveniles.

Which reminds me, before I get to the picture above (also at the Meadows today): everybody who tries to identify shorebirds ought to know a few basic facts.

1. Shorebirds (meaning sandpipers, plovers and allies) are often more easily identified by size, shape and behavior (which includes range and habitat) than by plumage, but. . .
2. If you are going to identify shorebirds using plumage, you have to first know what plumage they are in.
3. Shorebirds have three main plumages plus transitional stages in between.  These are: juvenal plumage (for the retentive types, juvenal refers to the plumage while juvenile refers to the bird); adult breeding (also known as alternate); and adult non-breeding (also known as basic, or winter).  Many shorebirds also wear a first-summer plumage, which is a not-quite-adult plumage that young, often non-breeding one-year olds wear in the spring and summer following their birth year.
4.  In general, juvenal plumage is neat and uniform in wear, since all the feathers were grown at once, and often features neat patterning, especially buff or light edging to the upperpart feathers. In some species, e.g. Least Sandpiper, juvenal plumage can be quite bright and beautiful.
5. In general, adult breeding plumage features the strongest patterning and brightest colors, at least when fresh (in spring). In fall, breeding plumage becomes worn and less colorful. Many shorebird species adults will appear in the mid-Atlantic on southbound migration in worn breeding plumage transitioning to non-breeding plumage, i.e. wearing a mixture of older breeding feathers and newer but plainer non-breeding feathers.
6. In general, non-breeding or winter plumage is the plainest, featuring varying shades of gray above and white below.  Then the damn things all seem to look alike, color-wise, but remain quite different in their size, shape and behavior.

[A slight digression: back in the dark ages of approximately the early 1980's, if you were a birder, you would have given your left foot to have some seasoned veteran tell you the six simple points outlined above, because the Peterson and Golden Field Guides of that time weren't doing it. I owe a thank-you to Don Roberson, who in his November, 1982 "Changing Seasons" summation in the old American Birds magazine succinctly spelled out the plumage information in item #3 above, and also spoke to shorebird migration timing, because in so doing he got me thinking about the rest and so moved me years ahead in the game of identifying shorebirds. I xeroxed Roberson's article and tucked it away, and still have it.]

OK, so. . . White-rumped Sandpiper.  Here's one more thing that new birders need to keep in mind: you can't see a perched (or standing) bird's rump, because the wings cover it.  Experienced birders take this fact for granted, but lots of times folks new to our pastime want to know why, for example, Yellow-rumped Warblers don't have yellow rumps.  The answer is they do, but they have to lift their wings or fly for us to see it.

Yeah, okay, so today we were scoping the peep at the South Cape May Meadows and I hit a bird and my mind went "boink" - different. Different from the predominant Semipalmated Sandpipers and Least Sandpipers.  A little bigger, a little longer, a little more horizontal in stance, and, a little grayer.  What I mean is, a little (but noticeably) darker gray. Which is characteristic of the non-breeding feathers of White-rumped Sandpipers as compared to Semipalmated Sandpipers.  They're not quite as sooty looking as winter Long-billed Dowitchers, but it's a color that, with practice, can call your attention to them.

The photo above, taken Friday, August 7, 2015, shows a White-rumped Sandpiper adult on the left, in worn breeding plumage molting to winter (basic) plumage, next to an adult Semipalmated Sandpiper on the right in basically the same plumage state but wearing more breeding feathers (which are more patterned) than the White-rumped is.

A few particulars you can look for on White-rumpeds, other than those already mentioned, are: the prominent white eyebrow contrasting with a darker head; the attenuated look to the rear end created by the fact that the wingtips extend past the tail, while on all the other "peep" except Baird's, the wingtips fall even with the tail (you have to look carefully to see this), and, as long as a little breeding plumage is remaining, white-rumps have streaking extending well down the flanks.  On this individual, I could see just a couple remaining spots under the wing in front of and just behind the legs, but those spots are excellent field marks. A great clinching mark on White-rumped Sandpiper is the pale reddish base to the lower mandible, when you can see it, but on this bird I could not, even at 60X on a fancy scope. This is one of those field marks that when you see it, it works, but when you don't, it may still be there. So, if you see it, use it; if you don't see it, that doesn't mean it's not there.

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