The bill, always black, is deep at the base and tapers sharply to a point. Often, a subtle down-curve near the tip is visible, especially in long-billed individuals. Examples of this: Fig. 1, Fig. 3, Fig. 4, Fig. 7, Fig. 14.

Female Western Sandpiper has a very long bill that is usually unmistakable in the field. See Fig. 13, which juxtaposes male and female Semipalmated Sandpipers (SESA) with a long-billed female Western Sandpiper.

Winter (basic) plumage of Western Sandpiper is paler and grayer than the same plumage on Semipalmated Sandpiper or Least Sandpiper (LESA).

Many Westerns winter farther north than the other two small Calidris species and undergo the molt to winter plumage earlier in the fall, often in September; see Fig. 1 and Fig. 16, which show a number of Western Sandpiper in New Jersey completely molted to winter plumage by September 23. Winter (basic) feather pattern is pale gray bisected by a sharp dark shaft and edged with a very narrow pale margin.

The bird in Fig. 2, is a young bird in winter (basic) plumage with a few juvenile rusty scapular feathers remaining.

Beginning in early spring, winter (basic) plumage is slowly replaced by alternate plumage; see Fig. 4.

Spring (alternate) feathers have wide dark centers and wide pale margins. The bases of many of the feathers have a strong rufous tone. Most of the rufous is concentrated in scapular feathers. The crown and the area behind the eye also become suffused with rufous. Males in alternate plumage are often more colorful than females; see Fig. 5, Fig. 6, Fig. 7.

Alternate-plumaged birds have breasts that are strongly streaked with arrow-shaped marks and streaks along the flanks; see Fig. 6.

Alternate plumage on birds reaching their first year of life (fledged the previous summer) is usually less colorful than alternate (breeding) plumage on birds two years old or older.

Spring (alternate) and summer (alternate) are the same plumage; however, as seasons advance, feather margins become worn, colors fade and the plumage looks different. Compare the broad pale margins of spring (alternate) feathers ( Fig. 7, photo taken in May) with the worn, narrow fringes of summer (alternate) feathers ( Fig. 8, photo taken in August).

Beginning in July, summer (alternate) plumaged WESA begins the molt to winter (basic) plumage and the birds display a salt-and-pepper appearance as the worn, dark older feathers are replaced with new paler feathers with thin, dark central shafts ; see Fig. 8, Fig. 9.

Newly fledged young birds arrive in New England from the Arctic in late summer, displaying the characteristic fresh, evenly patterned, scaly look of all young shorebirds. The upper scapular feathers on these birds nearly always have dark centers and rufous margins; see Fig. 10, Fig. 11, Fig. 14.

Fig. 12 illustrates a juvenile bird partially molted to winter (basic) plumage in early September.

Leg color ranges from dark gray to dark green to black.

When these birds walk in the sand and wrack, it may be possible to see the partial palmations (webbing) between the toes; see, Fig. 1, Fig. 6, Fig. 10, Fig. 11.

Western Sandpiper breeds in far northwestern Alaska and easternmost Siberia. The breeding habitat of Western Sandpiper is coastal uplands, occasionally lower mountain slopes with scattered low or dwarf trees, always in close proximity to wetlands where they feed. During migrations, coastal Western Sandpipers feed on the ocean shore, running back and forth at the water line. Due to their slightly longer legs and bill, they often feed in deeper water than Semipalmated Sandpipers.

At inland sites, the birds feed on the margins of shallow lakes or ponds.

In winter, coastal areas with fine sand or mud are preferred feeding sites. Western Sandpiper food consists of small insects, marine worms and small bivalves. They also feed on surface biofilm, a “soup” of diatoms and microbes churned up in coastal waters. At higher tides, Western Sandpiper roosts with Sanderling (SAND) and other sandpipers in dense flocks on higher dunes, sometimes on rock jetties or breakwaters; see Fig. 16.

In spring, a few Western Sandpiper individuals arrive in Massachusetts in early to mid-May; see Fig. 7. Fall birds are far more numerous than spring birds on the New England coast. Molting fall birds in summer (alternate) or juvenile plumage may be found from late August to October.

Western Sandpiper winters primarily on the west coasts of North America, Central America and northern South America from British Columbia to Peru.

A portion of the Western Sandpiper population winters on the eastern coast of the United States from New Jersey south to Florida, along the coast of Texas, down the eastern coast of Central America and on the northern coast of Venezuela.

Western and Semipalmated Sandpipers (WESA, SESA) are close in size and shape. In the spring, the rare Western Sandpiper individual in New England, with its distinctive alternate plumage, is rather easy to pick out among the hordes of Semipalmated Sandpiper migrants. In the fall, far more Western Sandpiper individuals arrive on the New England coast before heading south. Due to variations and overlap in bill length and variations in feather wear and molt, it is not always possible to separate WESA from SESA in the field, especially juveniles. It is safest to count as Western Sandpiper only individuals with long bills and some rufous in the upper scapulars. The situation is more complicated from New Jersey south because many more Western Sandpiper mix with the migrant flocks of Semipalmated Sandpipers during fall migration at more southerly latitudes along the east coast of North America.

Note the following:

• The rufous color in spring and summer (alternate) Western Sandpiper upperparts is concentrated in the crown, cheeks and scapulars, contrasting with the gray of the rest of the upperparts. Semipalmated Sandpipers in alternate plumage may show some rusty on the crown and behind the eye but not the bright rufous patches typical of Western Sandpiper.
• In alternate plumage, Semipalmated Sandpiper has a streaky breast band and some streaks and flecks extend to the flanks. Western Sandpiper in that plumage often has arrow-shaped marks on the breast and flanks; see Fig. 7.
• Many Western Sandpiper winter in southeastern US, so their molt to winter (basic) plumage occurs early, often by September.
• Female Western Sandpiper have very long bills and are usually unmistakable in the field; see Fig. 13, which juxtaposes some Semipalmated Sandpipers (male and female) with a long-billed (female) Western Sandpiper.
• The longest-billed (female) Western Sandpiper and shortest-billed (male) SESA are easy to pick out in a flock. Others, not so easy.
• Female SESA may have bills that are longer than male WESA. This is especially the case with the eastern long-billed SESA population; see discussion of long-billed birds in the Semipalmated Sandpiper species write-up.
• Small differences in perceived bill length (as opposed to measured in-hand length) are difficult to judge. Therefore, except in the case of extremely long-billed birds (female Western Sandpiper) or short-billed birds (male Semipalmated Sandpiper), is it not safe to use bill-length as the sole criterion for determining species. Other features are helpful; in juvenile birds, even a few rufous feathers on the upper scapulars combined with the long bill are the safest method for distinguishing Western Sandpiper; see the section on plumage.
• Western Sandpiper and Semipalmated Sandpiper both have partial palmations (webbing) between the toes.
• In late summer and fall, Western Sandpipers molt their flight feathers during migration; Semipalmated Sandpipers almost never do until they reach their wintering areas. In a flying flock in that season, birds with missing or half-grown flight feathers are most likely Western Sandpiper.
• On the bird in Fig. 11, note that the lower scapulars have anchor-shaped center spots. This is somewhat useful in distinguishing juvenile Western Sandpiper, but many Semipalmated Sandpiper juveniles have similar markings on the lower scapulars. These marks are useful in separating American dark-legged small Calidris sandpipers from Eurasian ones.

Sanderling (SAND) and Western Sandpiper (WESA) are quite different in size; SAND is approximately 20% larger.

• The rufous in alternate-plumaged Western Sandpiper is primarily on the crown, cheeks and scapulars. On alternate-plumaged Sanderling, cinnamon-rufous and black feathers are speckled evenly on the mantle, neck, face, head and breast; see Fig. 15.
• The juvenile plumage of SAND and Western Sandpiper is highly patterned. WESA displays a scaly brown-and-white pattern; Sanderling is boldly checkered black-and-white.
• Sanderling winter (basic) mantle plumage is the palest of grays, compared to the brownish gray of Western Sandpiper; see Fig. 16.