The juvenal plumage is much like that of the summer adult, except that the feathers of the mantle, scapulars, and the median and lesser wing coverts are edged with brighter colors, "tawny," "ochraceous-buff," and creamy white; and the breast is more buffy or yellowish. This plumage is apparently worn all through the fall and winter or until the first prenuptial molt in February and March, when the body plumage is renewed. At the first postnuptial molt, the next summer, the young bird becomes indistinguishable from the adult, having molted the entire plumage.
Adults have a partial prenuptial molt in the spring, from February to June, which involves the body plumage, except the back and rump and some of the scapulars, tertials, and wing coverts. The complete postnuptial molt of adults is much prolonged; the body molt begins in August, but the wings are not molted until the bird reaches its winter home, beginning in October and often lasting until February. Two adult females taken by Doctor Wetmore (1926) on September 9 in Paraguay "were in worn breeding plumage with no indication of molt." And one shot in Uruguay February 8 had renewed all but a few feathers of the entire plumage, while a male taken the same day was molting its primaries. There is very little difference between the summer and winter plumages; the feather edgings of the upper parts are more rufous in summer and more ashy in winter.
Food.—According to Preble and McAtee (1923), the contents of 21 well-filled gizzards of this species consisted principally of "flies (Diptera), 54.5 per cent; amphipods, 22.3 per cent; vegetable matter, chiefly algae, 10.5 per cent; beetles, 8 per cent; Hymenoptera, 2.1 per cent; and bugs (Hemiptera), 1.3 per cent." Other things eaten were mites, spiders, and caddis fly larvae and a few seeds of grass, lupine, and violet. P. L. Hatch (1892) says that "their food is principally crickets in spring, interlarded with various dry-land larvae, small beetles, and ground worms. In the fall the grasshoppers are first chosen, after which crickets and whatever other insects prevail at this season." Birds taken by B. S. Bowdish (1902) in Porto Rico had eaten fiddler crabs. Pectoral sandpipers feed mainly in grassy meadows, more or less dry, and their food is chiefly insects.
Behavior.—On the grassy salt meadows, where we usually find it, I have often been impressed with the resemblance of this sandpiper and the Wilson snipe, both in appearance and in behavior. It is often found in wisps or scattered flocks, the individuals widely separated and crouching in the grass. Often it flushes close at hand with a startling harsh cry and dashes hurriedly away with a zigzag flight. Sometimes it flutters away for only a short distance and drops quickly into the grass. Again it makes a long flight, circling high in the air and then pitches down suddenly in some distant part of the marsh, or perhaps near the starting point. Though erratic at first, the flight is swift and direct when well under way. They sometimes fly in flocks like other sandpipers, but more often they are flushed singly. They usually flock by themselves but are sometimes associated, purely fortuitously I believe, with other species that frequent similar feeding grounds, such as Wilson snipe, Baird, least or semipalmated sandpipers.
The pectoral sandpiper has another snipelike habit of standing motionless in the grass, relying on its concealing coloration, where its striped plumage renders it almost invisible, even in plain sight. It moves about slowly while feeding, probing in the mud with rapid strokes. Often it stands perfectly still with its head held high, watching an intruder; the dark markings on its neck end abruptly on the white breast, breaking up the outline and helping the bird to fade into the background. It is occasionally seen swimming across a narrow creek or channel.
Voice.—This is a rather noisy bird, especially so on its breeding ground, and its short, sharp flight notes are quite characteristic of the "creaker." Mr. Nichols contributes the following good description of them:
The notes of the pectoral sandpiper have a reedy character, intermediate in tone between the clearer calls of most shore birds and the hoarse cry of the Wilson's snipe. This is in keeping with its habits. Its characteristic flight note is a loud reedy kerr, resembling that of the semipalmated sandpiper (cherk) more closely than any other shore bird call, but recognizably heavier. Rarely in flight, the kerr varies into or is replaced by a near-whistled krru. On being flushed it often has hoarse, hurried cheeping notes, analogous with similar harsher notes of the Wilson's snipe. When in a flock of its own kind, alert and on the move, it has a short, snappy flocking note, a chorus of tcheps or chips. To my ear its flushing note is more or less a combination of flight note and flocking note, and it may reasonably be so. The flocking note communicates alertness to near-by members of a flock; the flight note is used more emphatically by birds separated from their companions or in active flight and disposed for companionship, whereas on being flushed the bird is signaling to possible companions; but as it has been feeding singly, concealed from such others as there may be by the grass, their distance is uncertain.
Field marks.—The pale-gray, almost white, tail with its dark, almost black, center and rump, is conspicuous in flight; a pale stripe in the wing is less noticeable. The snipelike colors of the upper parts, the dark, heavily streaked breast, contrasted sharply with the white under parts, and the short olive-yellow legs are good field marks when the bird is standing. The males are much larger than the females, which is unusual among shore birds.
Fall.—Regarding their departure from their breeding grounds, Murdoch (1885) says: