The name “sandpiper” is a poor fit for most members of the sandpiper family, Scolopacidae. A few species, such as Sanderling and Red Knot, show a preference for sandy shores, but the majority are “mudpipers,” seeking out muddy pond edges, estuaries, or tidal flats. A few are “grasspipers,” often in open fields far from the water’s edge. The Pectoral Sandpiper, a long-distance migrant from southern latitudes to the high Arctic regions of North America and Siberia, is a classic example of the “grasspipers.”
On average, compared to other bird groups, sandpipers and other shorebirds tend to migrate late in spring and early in fall. The Pectoral Sandpiper breaks that pattern, beginning to move north quite early in spring. Even though the species winters in South America, all the way to southern Argentina, northbound migrants begin to appear on the central Great Plains and near the Great Lakes by early March — or even late February — long before it would be practical for them to reach their Arctic breeding grounds. In fall, they have a prolonged migration season; some adults appear far south of the Arctic by the beginning of July, and many migrants are still at middle latitudes in late November.
Pectoral Sandpiper is classified in the genus Calidris. This group includes the smallest sandpipers, the so-called “peeps” and stints, as well as some medium-sized species like Sanderling and Dunlin, and a few larger ones like Red Knot. Pectoral Sandpiper is one of the medium-sized members of the group, but size is tricky for this species: Males average about 10 percent larger than females and can be as much as 20 percent larger. So even when it’s possible to make direct comparisons to other birds, size may not be as helpful for ID as it would be in other shorebirds.
All the species likely to be confused with Pectoral Sandpiper are other members of the genus Calidris, so our comparisons can focus there. The Least Sandpiper is superficially similar, generally brown and with yellow legs, but it’s much smaller with a distinctly different shape. Baird’s Sandpiper is closer to the size of Pectoral, and often shows a similar pattern to the underparts, with a streaked brown chest contrasting with the white belly. Its legs are black, not yellow, but this isn’t always a helpful mark, since the legs of shorebirds can be discolored or hidden.
In distinguishing these species, shape is the best field mark. For birders experienced with shorebirds, shape is often the number one clue for ID, backed up by behavioral traits. Plumage colors and other standard field marks come in a distant third. See the caption notes about the shapes of Least and Baird’s Sandpipers, and study the photos for more subtle points. Male Pectorals displaying on the breeding grounds puff themselves up into wild shapes, but for most of the year, the overall proportions of the species are readily recognized with practice.
Key field marks
- Upperparts brownish, with pale lengthwise marks
- Face finely streaked, with darker cap and lores
- Bill a little longer than head, slightly curved, usually pale at base
- Long wingtips, extending to tip of tail or slightly beyond
- Brown streaking on chest cuts off sharply at edge of white belly
- Legs are yellow to greenish yellow
What to look for
Size and shape. Smaller than Red Knot and larger than Least Sandpiper, with males larger than females. Legs and bill about average length for sandpipers in this size range.
Overall color. Brownish at all seasons, averaging a little grayer in winter. Fresh fall juveniles are a warmer or more reddish brown.
Bill. A little longer than head, thin, tapered at tip, slightly downcurved. Black at tip but with variable amount of yellow to brown at base.
Underparts. Always shows a sharp demarcation between the streaked brown chest and clean white belly.
Face. Contrasting darker lores (between eye and bill) and cap, but otherwise finely streaked without strong pattern.
Especially for newcomers to shorebird ID, Least Sandpiper might be confused with Pectoral Sandpiper, simply because both are brownish birds with greenish yellow legs. The Least is much smaller, averaging six inches long to the Pectoral’s eight and one-half inches, but it can be very difficult to judge the size of a bird on open mudflats, with nothing nearby for direct comparison. With practice, though, Least Sandpiper is easily distinguished by shape. It’s a compact bird with a relatively short neck, short legs, and short body, lacking the stretched-out look of Pectoral Sandpiper. Its bill, usually solid black, is no longer than its head, and it tapers to a fine point, often looking slightly drooped at the tip.
Baird’s Sandpiper is another “grasspiper” like the Pectoral, sometimes seen in open fields away from water. It’s larger than the classic “peeps” (such as Least Sandpiper), and like the Pectoral Sandpiper, it has strong brown tones and a sharp division between streaked brown chest and white belly. Leg color differs — black on Baird’s, greenish yellow on Pectoral — but this isn’t always helpful in the field, because the legs can be discolored by mud. Note the elongated shape of Baird’s, with long wingtips extending well past the tip of the tail, and the straighter, solidly black bill. Juvenile Baird’s in fall are easier to separate, with warm buff-brown heads and with whitish feather edgings giving the back a “scaly” appearance.
The Pectoral Sandpiper earns its name at breeding grounds on high Arctic tundra. The male develops a fatty, inflatable sac in the throat and chest (pectoral) area. This fleshy sac is extended greatly during displays, and in between, it sags loosely, as on the bird in this photo, making the black bases of the feathers very conspicuous. Each male defends a territory, usually on slightly raised ground, and performs flight displays there to attract females. He may mate with multiple females, and no pair bond is formed; the female may go off to place her nest somewhere outside the male’s display territory, and the male plays no part in incubating the eggs or tending to the young.
In his remarkable display flight, the male Pectoral Sandpiper flies low over the tundra, puffing out his inflatable chest sac to a ridiculous degree and giving voice to a deep, resonant, unbirdlike series of hoots. After 10 to 15 seconds of this, he stops the hooting, deflates the chest sac, and starts alternating quick flutters with slow glides, hanging awkwardly in the air with lowered head, as seen in this photo. The display flight may be repeated many times per hour. Satellite tracking studies have found that a male may stay on a certain territory for only a few days before moving on, sometimes hundreds of miles or more, prospecting for females elsewhere in the Arctic.
Many sandpipers show striking seasonal changes. In Pectoral Sandpipers, however, the differences are relatively subtle. Compared to breeding adults, juveniles look only slightly more colorful, while nonbreeding birds are only a little plainer and grayer. The full nonbreeding plumage of Pectoral Sandpiper is seldom seen in North America, since they molt mostly on the wintering grounds, so adults seen in fall migration look like worn and patchy versions of their spring finery. In that context, a fall juvenile can be picked out by the clean, crisp appearance of its upperparts, with sharp reddish brown and white edges on the scapular feathers (above the wings). The sharp demarcation between streaked chest and white belly still makes a good field mark.
Breeding in eastern Siberia, the Sharp-tailed Sandpiper is a regular fall migrant in southwestern Alaska and a rare but annual visitor to the Pacific Northwest, with scattered records elsewhere throughout North America. Adults can be very similar to Pectoral Sandpipers, differing mainly in the lack of a distinct cutoff between white belly and patterned chest. Fortunately, the great majority of Sharp-taileds occurring in North America are fall juveniles. This is a colorful plumage, with reddish brown cap and warm buff wash across the chest; fine streaking on the underparts is mostly limited to the sides of the chest. The supercilium (eyebrow) behind the eye usually looks broad, and the base of the bill shows only a limited pale area.
When it comes to reproduction and raising young, in most bird species, males take the lead in courtship, and females do the majority of the work of incubation and tending to the offspring. There are many variations on this pattern, however, and some conspicuous exceptions. The sandpiper family is notable for demonstrating a wide spectrum of reproductive strategies.
In the phalaropes, those odd swimming sandpipers, the female is dominant. She courts a male, lays a clutch of eggs, and leaves the male to incubate them. Female phalaropes are much more colorful than males, making this behavior easy to spot. Less noticeable is the same behavior in the widespread Spotted Sandpiper; a female may have several mates, laying a clutch for each to tend. In many sandpipers, both sexes share incubation duties, but the female departs shortly after the eggs hatch (or even before they hatch), leaving the male to raise the young.
At the other end of the spectrum are a few sandpipers in which males are promiscuous, forming no pair bond, and females do all the work of incubation and tending the young. The Ruff, an Eastern Hemisphere species, is the extreme example. Males, bizarrely ornate in breeding plumage, gather on display grounds and dance to attract females. In North America, Buff-breasted Sandpiper and Pectoral Sandpiper have less elaborate versions of the same behavior.
This article was first published in the March/April 2022 issue of BirdWatching Magazine.