The most common loud call of the western sandpiper has the ee sound found in the kreep of the least sandpiper, a plaintive quality as in the voice of the sanderling, and suggests somewhat the squawk of a young robin. It is variable and may be written chee-rp, cheep, or chir-eep. It seems to be the flight note of the species, corresponding to the cherk of the semipalmated sandpiper, and is also used by a bird on the ground calling to others in the air which alight with it, as such flight notes sometimes are. Its closest resemblance with a note of the semipalmated is to the serup sometimes heard from that bird when flushing.
Some of the calls of the western are apparently indistinguishable from those of the semipalmated sandpiper, but as studied on the northwest coast of Florida, where it greatly outnumbered the other form, more seemed different. Birds took wing with a sirp, or at another time a chir-ir-ip, which heard also in a medley of variations from a flock already on the wing, suggesting the notes of the horned lark, may be more or less analogous with the short flocking note of the semipalmated sandpiper.
Field marks.—It is most difficult and often impossible to distinguish between the western and the semipalmated sandpipers in life; and I have experienced difficulty in distinguishing between them even in the hand. The western has a longer bill, and I believe that the bill measurements of corresponding sexes do not overlap, though they approach very closely; but the longest-billed female semipalmated may have a longer bill than the shortest-billed male western. In spring and summer plumages the western shows much more rufous in the upper parts and is more conspicuously and more heavily streaked on the breast, but in winter plumage the two species are very much alike. Mr. Nichols has given me a few characters by which this species can be recognized even in winter; he calls it "a somewhat larger, rangier, paler, grayer bird" than the semipalmated; it also has "better developed white stripes over the eyes which meet more broadly on the forehead, the top of the head is not so dark, its dark auricular area is not so prominent, the markings on the top, and particularly on the sides, of the head and neck are finer.
As to the bills, he says:
There is a subtle difference in their bills, however, which I have frequently noticed in life and once or twice checked by taking specimens. The bill of a long-billed semipalmated sandpiper is quite straight and becomes slender toward the end; that of a short-billed western is not so slender toward the end and with just an appreciable downward bend before its tip. In long-billed individuals of the western sandpiper the bill becomes slender toward the end and frequently has a decided drop at the tip. Such birds are unmistakably different to anyone thoroughly familiar with the semipalmated sandpiper.
Fall.—Like many other waders, these little sandpipers begin to move off their breeding grounds at a very early date. As early as June 21, 1914, F. S. Hersey saw western sandpipers flocking at the mouth of the Yukon River, Alaska. Some of the flocks contained from 40 to 60 birds. The larger flocks were all of this species, but the smaller flocks often contained one long-billed dowitcher.
Doctor Nelson (1887) says, of its fall wanderings:
Early in July the young are on the wing and begin to gather in flocks toward the 1st of August. The last of these birds are seen on the coast of Norton Sound and the Yukon mouth the 1st of October. Although it is not recorded from the Seal and Aleutian Islands, I have seen the bird at St. Lawrence Island, south of Bering Straits, and at several points along the northeastern coast of Siberia, and it frequents the Arctic coasts of Alaska in addition to being found throughout the interior along streams where suitable flats occur. Murdoch notes it as a fall visitor at Point Barrow. It has been found in abundance on the southeast coast of the Territory, where it occurs during the migrations.