Shorebird ID Challenge: The Answers

 

Pectoral Sandpipers -- Birds “A” and “B,” which appeared at the far left and far right of the upper picture used in this ID challenge, are juvenile Pectoral Sandpipers. In the original image, which shows all six birds, it is apparent that these two birds are larger than the other species. Pectorals show proportions that make them look like an oversized “peep.” Their bills are about the length of their heads (nape to the base of the bill). They are not particularly long-legged, and the folded wingtips extend just a bit past the end of the tail. It should be noted that Pectorals are long-distance migrants, so they generally appear fairly long-winged when seen in profile (see lefthand bird above).

This juvenile Pectoral, also photographed at Soap Lake, Washington on 5 September 2008, provides a more close up view. (Photo taken by David Irons using a Panasonic Lumix DMC-FZ8 camera).

The upperparts of a juvenile Pectoral exhibit the following characteristics. It shows a solid rusty brown crown that is bordered by a fairly broad whitish supercilium (the obvious light stripe above the eye); the rest of the face (below the supercilium) is warm reddish brown with some very fine dark streaking. The back feathers are mostly brown at the base, black near the tip, and are crisply edged with rufous and/or white. Several rows of back feathers have rufous margins to the inner webs and white margins to the outer webs, which creates several white lines running down the back. This is shown well by the lefthand bird above. The tertials (long folded innermost wing feathers that extend out over the tail) are mostly black with bright rufous to rufous-buff edgings.

The underparts of a Pectoral are mostly white, except for the breast, which is brown to brownish-buff with lots of fine crisp dark streaks. The brown on the lower breast typically comes to a bit of a point in the middle and ends abruptly where the white starts.

The bill of a Pectoral is mostly dark, fairly heavy, and usually appears to be slightly down-curved. When seen at close range, the base of the bill (particularly the lower mandible) varies from brownish to dingy orange.  Their legs are a straw-colored yellow. Apparent leg coloration is variable depending on lighting conditions and the nature of the substrate that the birds are feeding in. This image was taken late in the day at a site with very dark gooey mud, hence the rather dingy greenish-brown look to the legs on these Pecs. However, even in these conditions it is apparent that their legs are not black.

Those who responded to the ID challenge had no difficulty identifying these birds as Pectorals. If seen well, they are rarely confused with other species. The most likely species to be confused with Pectoral is actually Least Sandpiper, which looks nearly identical in plumage and proportion, but is much smaller. When seen together they are easily separable by size, but one or the other seen singly at a distance can occasionally fool even experienced observers.

This group of small sandpipers was at Soap Lake, Washington 5 September 2008. (Photo taken by David Irons using a Panasonic Lumix DMC-FZ8 camera).

The Peeps -- Those who posted their identifications of the birds pictured above were overwhelmingly correct. The bottom bird (challenge bird "E") is a juvenile Least Sandpiper. As stated above, Leasts are very similar in overall plumage to a Pectoral Sandpiper. They have comparatively short greenish-yellow legs. Their back feathers are dark brown to black with rufous and white edgings. Like Pectorals, they also show multiple sets of white lines (often referred to as “braces”) running down their backs. The bill of a Least is shorter and thinner overall than other North American peeps (Western and Semipalmated sandpipers), and often appears slightly drooped towards the tip (as is the case with the bird above).

The two birds on the top left (challenge birds "C" and "D") are juvenile Semipalmated Sandpipers. Bill size and shape comprise one of the best field marks for separating juvenile Semipalmateds from the very similar Western Sandpiper. The bill of a Semi is quite thick, short, straight, and shows little taper. The tip usually looks quite blunt, and at close range may show a bit of expansion at the end (sometimes referred to as a “bulbous tip”). Unlike Leasts, their legs and feet usually look black. Note that some Semipalmated Sandpipers have dusky green legs.

This close-up of a juvenile Semipalmated Sandpiper, photographed at Port Susan Bay, Washington on 7 August 2007, shows many of the typical features exhibited by this species. Note the scaly upperparts and the lack of rufous in the scapulars, the short, thick, blunt-tipped bill, the smudginess around the eye, the lack of well-defined white braces on the back, and the fairly dark brown crown. As mentioned above, some juvenile Semis have greenish legs, which is obviously the case with this individual. (Photo by Steven Mlodinow using a Panasonic Lumix DMC-FZ50 camera)

In overall plumage, Semipalmated Sandpipers usually look fairly even colored (gray-brown to earthy brown) above, and they rarely exhibit much contrast between the scapular feathers (where the wing connects to the body) and the wing coverts (the forward feathers on the folded wing). Their crowns are fairly solid brown with fine dark streaking and they have a bit of a “capped” look. The wing coverts have dark centers that vary from black to very dark gray brown and don’t seem to have much of an internal pattern. The edges of the back and wing covert feathers vary from pale gray to buff, typically creating a “scaly” look to the upperparts of a Semi. The long tertial feathers typically show gray to gray-brown centers with pale gray edges.

The two Semipalmateds above show a discernible difference in the brightness of the back pattern.  The front bird (challenge bird "D") shows very little white on the margins of the scapular feathers, while the back bird shows a fair amount of white edging on the scaps and seems a little more patterned overall. However, the margins of the back and scapular feathers of a Semipalmated Sandpiper do not create the obvious lines (“braces”) shown by other “peeps” and “stints.” I find that juvenile Semipalmated Sandpipers often have a “smudgy” look around the eye, and the area directly behind the eye is usually fairly dark brown. This mark is shown by both of the Semipalmateds in this image.

The top right bird (challenge bird "F") is a juvenile Western Sandpiper. Westerns are slightly larger than the other two  expected North American small Calidrids (Least and Semipalmated sandpipers). Like most Semipalmateds, they also have black legs. Their bills are fairly long, although this can be quite variable depending on the sex of the bird. Females have longer bills than males, and the shortest-billed males might suggest a Semipalmated Sandpiper. However, as a rule, Westerns have noticeably longer bills than Semis, and their bills will almost always look somewhat drooped and more tapered towards the tip. The amount of apparent droop and taper is more noticeably on longer-billed Westerns (like the presumed female above).

Westerns have more patterned upperparts than Semis overall with highly contrasting gray and rufous on the back and scaps. Their upper scapular feathers (at the sides of the back) are brightly edged with rufous on the inner margins and have broad white outer margins. This creates a bright line of rufous along the scaps that contrasts with gray tones on the back and the wing coverts. The white outer margins form a white line, which is quite obvious on this bird. The lower scapular feathers also show more pattern than those of a Semipalmated Sandpiper. They are gray to gray-brown at the base, and have a somewhat anchor-shaped black area towards the tip and black running back up along the shaft of the feather. These feathers show broad white margins, particularly on the tip and outer web, and the scapular feathers of a Western are a bit longer and more attenuated than the scapular feathers of a Semipalmated.

Though it is not shown on the bird in the ID challenge image, the area around and behind the eye is a bit less smudgy on a juvenile Western than it is on a  juvenile Semipalmated. Westerns usually show a faint wash of rufous behind the eye, but otherwise the face and crown are paler and grayer overall.

With practice, the structural and plumage differences described above can be learned and used effectively to sort out these similar species. Remember, when migrant shorebirds stop at your local estuary or muddy lake edge, they are urgently feeding in an effort to build up fat reserves needed for long migratory flights. This makes them quite approachable at times. If you move slowly, stop often and just stand still for a while before again proceeding slowly, you might find yourself within a few feet of these birds.

This image, taken at Florence, Oregon on 12 August 2008, shows nice comparison between a Western Sandpiper (left) and Least Sandpiper (right) in fresh juvenile plumage. Note the difference in bill length and thickness (Least's bill is slightly open making it look thicker than it is), the longer-legged appearance of the Western compared to the short-legged look of the Least, and the darker breast of the Least. This picture also captures the brightness of the rufous scapulars of the Western, which contrast noticeably with the mostly gray back and wing coverts. (Photo taken by David Irons using a Panasonic Lumix DMC-FZ8).

In most of North America, the Calidris sandpipers seen after August 1st will be about 90-95% juveniles. The adults that one is likely to see at this time of year will already be well along with their pre-basic molt, which gives them a rather motley and inconsistent- looking plumage. They will stand out like a sore thumb among the hordes of fresh-plumaged juveniles. If you look at the juvenile birds in these images, the plumage looks consistent, with no feathers that seem unmatched to the others. The feathers also look fresh with unworn edges.