The identification flight-call is a loud diagnostic _kreep_, distinguished by the [=e][=e] sound from any note of the semipalmated sandpiper.... In flushing, a least sandpiper sometimes utters a string of short unloud notes with or without the [=e][=e] sound, _quee-quee-quee-que_ or _queque_ to be followed almost immediately by some variation of the flight call, as it gets more fully under way. The flight note varies down to a _che_ and _cher_, not readily, if at all, distinguishable from similar calls of the semipalmated sandpiper.... When a flock are up and wheeling about a feeding spot to alight there again almost at once, they have sometimes a confiding little note _chu chu chu chu_, etc. It has also a whinny, a little less clearly enunciated than that of the semipalmated but almost identical with the same. _Field marks._--The small size of the least sandpiper distinguishes it readily from all the other sandpipers in this country except the semipalmated, with two exceptions to be noted later. As the least is more frequently found on tidal flats in the estuaries and in salt marshes, it is sometimes called the "mud peep," while the semipalmated, which especially delights in the sand beaches is called the "sand peep." Unfortunately this rule, although of general value, is far from absolute, and the birds often exchange places. The least sandpiper is more often found on the beach in the spring than in the fall. The semipalmation is, of course, a diagnostic mark in the hand, but only under exceptional circumstances can it be seen in the field. The color of the tarsus, however, is distinctive and can be made out in favorable light at a considerable distance. I have always thought it absolutely distinctive, but the published descriptions and plates of these two birds are often inaccurate. I have, therefore, compared the legs of both these species, freshly collected, with Ridgway's (1912) "Color Standards and Color Nomenclature." In the semipalmated sandpiper the tarsi of the adults are black and this is also the case in the juvenals except that there is a slight greenish tinge to be seen on close inspection. In the adult least sandpiper the tarsi are distinctly yellow with a faint greenish cast. They correspond best to the _sulphine yellow_ of Ridgway, while the toes, which shade off a little darker, are _citrine_. In the juvenal, there is more of a greenish tinge, and I have put the tarsi down as _oil yellow_, the toes shading into _yellowish oil green_. In deciding on these colors I have had the advice of an artist. The richer brown plumage of the back and the darker streakings and wash of the breast help to distinguish the least from the lighter and grayer semipalmated bird, but in the fall these distinctions are less marked in the adult. Even at this season, however, a least sandpiper on the beach in a flock of semipalmated stands out by its browner colors, and, in the