The eggs of the purple sandpiper are four in number and remarkably handsome. They vary in ground color from pale olive to pale buffish brown, boldly mottled, blotched, and streaked with reddish brown and very dark blackish brown. On some eggs the blotches are large, and chiefly distributed in an oblique direction round the large end; on others they are more evenly distributed over the entire surface; and on many a few very dark scratches, spots, or streaks are scattered here and there amongst the brown markings. The underlying markings are numerous and conspicuous, and are pale violet gray or grayish brown in color.
Frank Poynting's (1895) colored plate of 12 selected eggs well illustrates the great variation in the beautiful eggs of this species. There are two distinct types of ground color, green and buff. In the green types the colors vary from "yellowish glaucous" to a light shade of "grape green"; and in the buff types from "cream buff" to "dark olive buff." They are sometimes evenly, but more often irregularly, spotted and blotched with various shades of brown, "sepia," "bister," and "snuff brown," sometimes boldly marked with "chocolate" and "burnt umber" and sometimes with great splashes of "vinaceous brown" overlaid with blotches of "chestnut brown" and "bay," a handsome combination. The measurements of 100 eggs, supplied by Rev. F. C. R. Jourdain, average 37.3 by 26.5 millimeters; the eggs showing the four extremes measure 40 by 28, 35.1 by 26.6 and 37.3 by 24.8 millimeters.
Plumages.—The nestling is described in Witherby's Handbook (1920) as follows:
Fore part of crown warm buff; black-brown median line from base of upper mandible to crown; crown and upper parts velvety black-brown, down with numerous cream and warm buff tips; nape light buff, down with sooty-brown bases; from base of upper mandible above eye to nape a black-brown streak, another short one from base of lower mandible, ear coverts as crown; cheeks warm or light buff, down with black-brown tips; remaining under parts grayish white, down sooty brown toward base.
The juvenal plumage is much like that of the summer adult, except that the feathers of the crown are tipped with creamy white, as are also the central tail feathers; the feathers of the mantle and scapulars are edged with buffy white; and the wing coverts and tertials are broadly edged with the same color or tipped with pale pinkish buff. The juvenal body plumage is usually molted before the birds reach us on migration, when young birds, in first winter plumage, can be recognized by the broad white edgings of the median coverts and by a few retained scapulars and tertials. Some of these juvenal feathers are retained through the next, the partial prenuptial molt. Subsequent molts and plumages are as in the adult.
Adults have a complete postnuptial molt between August and November and a partial prenuptial molt from January to May; this latter involves most of the body plumage, but not all of the scapulars, back, rump, or upper tail coverts.
Food.—The favorite feeding places of purple sandpipers are the wave-washed rocky shores of islands or promontories along the seashore, with a decided preference for islands. Here, where the rocks are fringed with rockweed, waving in the restless waves, or covered with barnacles and various slimy products of the sea, these sure-footed little birds are quite at home on the slippery rocks, as they glean abundant food at the water's edge and skillfully avoid being washed away. Yarrell (1871) says that—
it may be seen busily employed turning over stones and searching among seaweed for the smaller shrimps and sandhoppers which are to be found there, and it also feeds on young crabs, marine insects, and the soft bodies of animals inhabiting small shells.
Witherby's Handbook (1920) gives its food as—