Mr. Mackay (1893) writes:
On the ground they are sluggish and not given to moving about much; unless very much harassed they are not nearly so vigilant as their companions, the black-bellied plover, but when they have become shy they are exceedingly wary and always on the alert for danger. When the incoming tide drives the knots from the flats they seek the marshes or some shoal which is sufficiently elevated to remain uncovered during high water; they also frequent the crest of the beaches. Here they generally remain quiet until the tide has fallen sufficiently to permit them to return again to the flats to feed. When on the marshes during high water they occupy some of the time in feeding, showing they are by no means dependent on the flats for all their food. They associate and mingle freely with the turnstone (Arenaria interpres), black-bellied plover (Charadrius squatarola), and red-backed sandpiper (Tringa alpina pacifica) as with their own kind, and apparently evince the same friendship toward the two former birds as prevails between the American golden plover (Charadrius dominicus) and the Eskimo curlew (Numenius borealis). I have heard of but one instance (at Revere, Mass., during a storm) of the knot being noted in the same flock with adult American golden plover. At this time there were three, one of which was shot. I have heard, however, of both adult and young knots mingling with young American golden plover, or "pale-bellies," as they are locally called.
Voice.—The same writer says:
They make two notes. One is soft, of two articulations, and sounds like the word "Wah-quoit" (by which name it is sometimes known on Cape Cod); although uttered low, it can be heard quite a distance. This note is particularly noticeable when flocks are coming to the decoys; it has a faint rolling sound similar to the note of the American golden plover (Charadrius dominicus) under the same conditions, only more subdued and faint. The other is a single note resembling a little honk. These birds will also respond to the note of the black-bellied plover (Charadrius squatarola) as readily as to their own when it is given with a whistle.
Roland C. Ross (1924) gives the following graphic description of the croaking note:
The common call is a low-pitched, hoarse "skeuk," the lowest and heaviest voice on the flats. It struck me as a dull croak, coming pretty regularly from the feeding birds, and especially strong when they took wing. A lone bird in joining the flock would croak his coming. The sound can be imitated in quality and form but in a higher pitch. Make the facial contortions necessary to "cluck" to a horse, but don't "cluck"; make it "skeuk," and locate it in the wisdom teeth on the side being dislocated. Pitch it low; it will still be two tones too high. At a distance the sucking or harsh quality is lost. A softer, more musical rendition is given when the birds are well bunched and feeding, which came to my ear as "chook."
John T. Nichols (1920) says: "The flight note of the knot is a low-pitched whistle, frequently in two parts, with a peculiar lisp or buzz in it, tlu tlu."
Doctor Ekblaw describes the notes heard on the breeding grounds as follows:
Four distinct calls characterize the mating and nesting season. Most common are two piercingly shrill calls uttered generally on the wing, one of them resembling wah-quoi and the other wee-a-whit, easily distinguished, but somewhat alike. The long-drawn-out coo-a-hee, or coo-hee, is a soft, flutelike call also given in flight, but nearly always back among the hills, far from the shore where the nests are hidden. This flutelike call appears to be a signal or recognition call. The fourth call is a sharp, querulous whit, whit, whit, almost like a cluck, often given singly, but more often many times repeated. When their nesting haunts are invaded or their feeding grounds disturbed this call expresses their displeasure.