The juvenal plumage appears first on the wings, scapulars, and sides of the breast; the primaries burst their sheaths before the young bird is half grown. In the juvenal plumage, as seen on migration in August, the crown is heavily streaked with blackish brown, the feathers being edged with light buff; the feathers of the back and scapulars have an outer border of light buff, then a black border, then another buff, and sometimes a faint black border inside of that; the greater and median wing coverts have a terminal buff and a subterminal black border; the tail feathers are edged with buff and the under parts are more or less suffused with pale buff. Probably the buff is brighter and deeper in fresh plumage and it fades out to white before this plumage is molted.
A postjuvenal molt takes place, between September and December, of the body plumage, some scapulars and some wing coverts. This produces the first winter plumage, which is like that of the adult, except for the retained juvenal scapulars and wing coverts. I have seen birds in this plumage as early as September 30. A partial prenuptial molt, similar to that of the adult, produces during the spring a first nuptial plumage in which young birds can be distinguished from adults by varying amounts of retained winter feathers. At the next complete molt, the first postnuptial young birds assume the fully adult winter plumage.
Adults have a partial prenuptial molt between February and June, involving most of the body plumage, but not all of the scapulars, wing coverts, and tertials. There is much individual variation in the time of this molt. I have seen birds in full nuptial plumage as early as March 21 and in full winter plumage as late as May 13. The complete postnuptial molt begins in July with the body molt, which is usually completed before October. I have seen adults in full nuptial plumage as late as September 6. The red-breasted birds reported by Mr. Mackay (1893) as shot on Cape Cod in December and February must have been exceptional cases of delayed or omitted molt; the February birds may have been cases of early spring molt.
Food.—Doctor Ekblaw says:
Their food when they first come to the North is scarce, and when the weather is unduly unfavorable they are hard put to it to find enough to live. They probe about the grasses and sedges on the wet moors and along the swales and pools, and sometimes wade breast deep into the water to pick out the small but abundant life that swarms in some of the pools, mostly crustacea and larvae. The upper mandible is relatively soft and pliant. Sometimes they search the tide pools left at low water, or poke about the rocks and gravel along shore.
Other Arctic explorers have referred to the scanty food of the knot in the north; H. Chichester Hart (1880) says that "of a number of knots' stomachs examined, only one contained any food; this consisted of two caterpillars, one bee, and pieces of an Alga;" Colonel Feilden (1879) saw knots "feeding eagerly on the buds of Saxifraga oppositifolia;" Mr. Manniche (1910) "saw them running on the snow eagerly occupied in picking up the seed of Carex and Lazula tufts, the ends of which here and there appeared over the snow." Later on, when the ponds and marshes are teeming with animal life, they have plenty of food.
With us, on migrations, the knots feed mainly on the sandy and stony beaches, moving deliberately along in compact groups close to the water's edge, probing in the sand for minute mollusks and small crustaceans. On the sandy beaches on the west coast of Florida, the wet sand is filled with minute shellfish known as Coquinas, on which the knots seemed to be feeding. They also feed to some extent on the mud flats and sand flats with the black-bellied plover, where they find marine insects and their larvae. Mr. Mackay (1893) says "they also eat the larvae of one of the cutworms (Noctuidae) which they obtain on the marshes," some of which he has found in their throats when shot. Edward H. Forbush (1912) says: "They are fond of the spawn of the horsefoot crab, which, often in company with the turnstone, they dig out of the sand, sometimes fighting the former birds before they can claim their share." W. L. McAtee (1911) says that they also feed on grasshoppers and on marine worms of the genus Nereis.
Behavior.—The knots fly swiftly in compact flocks, twisting and turning in unison like the smaller sandpipers, for which they might easily be mistaken at a distance. On the ground they are rather deliberate in their movements, generally grouped in compact bunches and all moving along together; they are less likely to scatter over their feeding grounds than other waders. When resting on the high beaches between tides they stand quietly in close groups, all facing the wind; their grey plumage renders them quite inconspicuous at such times. F. H. Allen tells me that he has seen half a dozen of them hopping about on one leg in shallow water; this may be a sort of game, frequently indulged in by many small waders.
Mr. Manniche (1910) says:
Peculiar to this species is its restless character. The resident couples would every day make long excursions, not only to seek food, but probably also for pleasure. Their great power of flight makes them able to do this without difficulty. In rapid high flight they are now here and now there. I often saw them set out in a northern direction high over the summits of the mountains or in a southern far out over the ice in the firths, to return after a short while.
In the breeding season the male is pugnacious and quarrelsome against birds of its own kin as well as against other small birds, which appear within his domain. Uttering a short cry he will fly up and pursue the intruder in the most violent manner and often he would follow it so far away, that I could not see them, even through my field glass. He would soon return, and having—triumphantly fluting—circled around several times, go down to his mate. I have seen the knot pursue even skuas.