Mr. Manniche (1910) gives a colored plate showing four ages of downy young sanderlings, which the above description fits. A nestling 7 days old shows the remiges about one-third grown, while the body is still all downy. Another nearly fully grown only 11 days old is still downy on the head, neck, rump, and crissum, but is nearly fully feathered on the mantle and wings, partly feathered on the under parts and the wings extend beyond the stump of a tail; it must be close to the flight stage. Such is the rapid development of these little Arctic birds that Mr. Manniche (1910) says that they can fly when 14 days old.
In fresh juvenal plumage in the Arctic the feathers of the crown, mantle, wing coverts, scapulars, and tertials are blackish brown, broadly tipped, and all except those of the crown are also notched, with buff; the sides of the head, neck, and breast are washed with buff; before these birds reach us on migration these buff tints have mostly faded out to creamy yellow or white; the feathers of the lower back, rump, and upper tail coverts are ashy brown or grayish buff, each with a dusky shaft streak and narrowly tipped with dusky; as these feathers are not molted during the first winter they produce a peculiar rump pattern by which young birds can be easily recognized. Young birds are in juvenal plumage when they arrive here, with conspicuous black and white backs. But the postjuvenal molt begins in September and is generally completed before November; this molt involves the body plumage, except the rump, and some of the wing coverts and tertials. The first winter plumage is like that of the adult, plain gray above and white below, except for the retained juvenal feathers as indicated above.
A partial, or perhaps nearly complete, prenuptial molt takes place in young birds between March and May, involving the body plumage, sometimes the tail and most of the scapulars and wing coverts. In this first nuptial plumage young birds are much like adults, but can be recognized by some retained wing coverts and tertials; the latter are shorter than in adults, reaching not quite to the tip of the fourth primary in the folded wing; in the adult wing the tertials reach nearly to the tip of the third primary. At the next molt, the first postnuptial, the adult winter plumage is assumed.
Adults have a complete postnuptial molt from July to October or later. The body plumage is molted first, mainly in August and September, and the wings later, mainly in October; specimens have been seen with primaries in molt in February and March, but these are probably abnormal. The prenuptial molt of adults is incomplete, involving nearly all of the body plumage, but not all of the feathers of the back, scapulars, tertials, or wing coverts. The fresh nuptial plumage in early May is veiled with broad grayish white tips, which soon wear away. There is great individual variation in the amount of red assumed and in the molting date.
Food.—The sanderling obtains most of its food by probing in the wet sand of the seashore or by picking up what is washed up and left by the receding waves. The former method is well described by Dr. Charles W. Townsend (1920) as follows:
On the hard wet sand of the beaches one may see in places the characteristic probings of the sanderling without a trace of their foot marks, and these may be the cause of considerable mystery to the uninitiated. While the semipalmated sandpiper runs about with his head down dabbing irregularly here and there, the sanderling vigorously probes the sand in a series of holes a quarter of an inch to an inch apart in straight or curving lines a foot to 2 feet long. Sometimes the probings are so near together that the line is almost a continuous one like the furrow of a miniature plough. The sand is thrown up in advance so that one can tell in which direction the bird is going. A close inspection of the probings often reveals their double character, showing that the bill was introduced partly open. The probings are for the minute sand fleas and other crustaceans in the sand, their principal food. I have seen sanderlings running about nimbly on the beach, catching the sand fleas which were hopping on the surface. I have also seen them catching flies. I have a record of one I shot in 1884, whose stomach was stuffed with small specimens of the common mussel, Mytilus edulis.
The food consists mainly of sand fleas, shrimps, and other small crustaceans, small mollusks, marine worms, flies, fly larvae, and other insects, and sometimes a few seeds. Early in the season in the Arctic regions when animal life of all kinds is scarce the sanderling is said to subsist on the buds of saxifrage and other plants, as well as bits of moss and algae.
Behavior.—I have always loved to walk by the seashore alone with Nature, and especially to tramp for miles over the hard sands of our ocean beaches, where the heaving bosom of the restless sea sends its flood of foaming breakers rolling up the steep slopes, cut into hills and valleys by the action of the waves. From the crest of the beach above or from the lonely sand dunes beyond comes the mellow whistle of the plover, disturbed in his reveries; out over the blue waters a few terns are flitting about or screaming in anxiety for their, now well grown, young perched on the beach. Flocks of small shore birds hurry past well out over the breakers, flashing light or dark, as they wheel and turn; and high overhead the big gray gulls are circling. But right at our feet is one of the characteristic features of the ocean beach, a little flock of feeding sanderlings, confiding little fellows, apparently unmindful of our presence. They run along ahead of us as fast as we can walk, their little black legs fairly twinkling with rapid motion. They are intent only on picking up their little bits of food and most skillfully avoid the incoming wave by running up the beach just ahead of it; occasionally a wave overtakes one when it flutters above it; then as the wave recedes they run rapidly down with it, quickly picking up what food they find. If we force them to fly, which they seem reluctant to do, they circle out over the waves and settle on the beach again a short distance ahead of us; by repeating this maneuver again and again they lead us on and on up the beach, until, tired of being disturbed, they finally make a wide circle out over the water around us and alight on the beach far behind us. Their flight is swift, direct, and generally low over the water, with less of the twistings and turnings so common among shore birds. They usually flock by themselves, but are often associated in small numbers with knots, small plovers, or other beach-loving species. When satiated with food or tired of strenuous activity, they retire to the crest of the beach, or the broad sloping sand plains beyond it, to rest and doze or preen their plumage. Here they stand or squat on the sand, often in immense flocks, all facing the wind. Their colors match their surroundings so well that they are not conspicuous and I have often been surprised to see them rise. These large flocks are generally wary and not easily approached. But small parties or single birds feeding along the surf line are very tame and if we sit quietly on the beach, they will often run up quite close to us. Like many other shore birds, they are fond of standing on one leg or even hopping about on it for a long time, as if one leg were missing; often a number of birds will be seen all doing this at the same time, as if playing a sort of game; but if we watch them long enough, the other leg will come down, for they are not cripples.
Voice.—J. T. Nichols writes to me of the limited vocabulary of this bird, as follows: