Sanderling, possible Semipalmated Sandpiper

Seen at Broughton Beach about 130PM today.

The Sanderling were mixed with about 10 Western Sandpipers.  The peep at bottom right looked to me like a Semipalmated Sandpiper.  The bird itself was clearly smaller than the Westerns, with a much shorter bill, and different body shape.  I've asked 2 birders whom I greatly respect and one thought it was a Semipalmated and the other thought it was a small Western.  Other opinions are welcomed.
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Comment by Shawneen Finnegan:  Andy had sent this photo to me privately before posting to OBOL and my response was that it was a Western Sandpiper. Andy had said he thought it looked different in size and shape, but sexual differences in Western Sandpipers can make them appear quite different from one another. Add to that the clinal and color differences in Semipalmated Sandpiper and it can get confusing.

Dave Irons's post about this bird essentially discusses this sexual difference and the how a bird's stance can affect how they look structurally such that one has to look at feather markings and patterns to determine what species it is. For example, many have wanted to identify an alarmed Least Sandpiper that is standing up tall on its toes as a Long-toed Stint because they appear uncharacteristically long-legged and long-necked. At that point one has to look at facial pattern and other features to suss out the identity. Like many species it isn't one field mark that is used, but several or many.

At first glance this peep looked structurally like a Western to my eye. Often Semis look stockier and more compact, at times potbellied, less elongated than a Western. Mind you it is stretched out but does look similar to the adjacent Westerns. Western's are described as looking front heavy and unbalanced, while Semis look more balanced.

The facial pattern also looks similar to the Westerns nearby. Semis often have a darker cheek and crown giving their face a more contrasty appearance while Westerns look pale. The nape on this bird is quite, adding to a less contrasty appearance. From my experience many Semis from the western side of the country look much shorter billed than ones that appear on the east side of the continent. This may be clinal, but some of the Semis back east have very long bills with slim tips that look very much like a Western.

The scapulars, at least the top visible ones, look rusty to me, favoring Western.

In good light juvenile Semis have dark olive legs that often look black like a Western's. The olive does darken to black later in the fall. Primary projection doesn't help because both are about the same in that regard (short).

The one thing about Semis is that they can really vary with how cold or warm they can appear. Some can be very rusty, but that rust is more uniformly spread across the wings and mantle. A few of these have appeared on the west coast and have caused great excitement because they were thought to be either a Little or Red-necked Stint. It is an unusual plumage and one to be aware of. This bird shows a bit of warmth to the edges of the lesser coverts (the feathers that are not typical of Western, yet there are photos of a Western in the BirdFellow gallery taken by Glenn Bartley (#18 and 24) that show an obvious Western with a warmer toned edges to these same feathers.

I can understand people taking different stances on this bird, because there is only one photo, the bill is blurry, and it is more subtly patterned than most Westerns. It is an interesting bird and thank Andy for bringing it to our attention.

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And by David Irons:  I tend to apply minimal value to apparent bill length and size in the final identification of small calidrid sandpipers ("peeps"). This is especially true when I'm looking at photos and even when I've looking at them in life. Western Sandpipers exhibit significant sexual dimorphism when it comes to size and particularly when it comes to bill length. The shortest-billed Westerns (males) can be suggestive of Semipalmated Sandpiper based on bill length and they are likely to look smaller as well. From what I see in this image, the other Westerns all seem to have long bills and they do appear slightly larger. I'm inclined to think that the they might all be females. This would explain why this one apparent male does appear to be smaller and shorter billed.

When I look through flocks of our most-expected peeps (Leasts and Western Sandpipers), I tend to use size, shape and bill length for sorting as I search for something less expected. However, once I pick out an individual that might be of interest, I turn my attention to the specifics of plumage pattern. If I think that I'm looking at a juv. Semipalmated Sandpiper, I look for uniformity in the coloration of the upper parts. Semis show very little if any contrast between the color of the mantle (back), scapulars (feathers at the shoulder), and the coverts (feathers covering the base of the flight feathers). On a Semi, these feathers tend to look dark-centered with poorly-defined internal markings and they have narrow whitish to buffy fringes. In my opinion, this creates a fairly uniform and slight scaly look to the upper parts.