Plumages.—The most remarkable thing about the downy young spoonbill sandpiper is the well developed spoon-shaped bill, even when first hatched. As will be seen by referring to Colonel Thayer's (1911) excellent colored plate, this is much shorter than the adult bill and the spatulate tip is more oval. The crown, back, rump, wings, and thighs are variegated with black, white, "ochraceous tawny" and paler buffs, dotted with white terminal tufts on the head, which form two white stripes from the eyes to the nape, and dotted with both white and buff tufts on the back and rump; the forehead, a superciliary stripe, the sides of the head, the throat, and the neck are "warm buff"; the rest of the under parts are white; a median frontal stripe, a loral stripe, and a malar spot are black.
The juvenal plumage I have never seen. Birds collected on the southward migration are apparently all in winter plumages; young birds are distinguishable from adults at this age. For descriptions of first winter and subsequent plumages I would refer the reader to Ridgway's Birds of North and Middle America. I have not studied sufficient material to work out the seasonal molts, but they are apparently similar to those of other small sandpipers of the genus Pisobia.
Food.—The food of the spoonbill sandpiper seems not to have been definitely determined, but Mr. Dixon (1918) watched a pair feeding, of which he says:
Our observations disclosed no peculiar advantage attending the singular shape of this sandpiper's bill, though careful watch was kept to see just how this member was used. On July 17, 1913, a pair of spoonbilled sandpipers was watched for half an hour as the two birds fed within 50 feet of the observer, concealed behind a sandy dune. Their favorite feeding ground was a fresh-water pond with a fringe of green algae about the sandy border. Under these conditions the birds used their bills, as any other sandpipers would, as probes to pick out insects or larvae from the algae. Occasionally one would hesitate a moment, when the vascular tip of the mandible quivered slightly as though the bird were straining something out of the green algae. At this time the bill was held at nearly right angles to the surface of the water; it was never used as a scoop along the surface.
Behavior.—I must again quote from Mr. Dixon (1918), who has furnished most of our information about this little known species. Referring to behavior and recognition marks he writes:
In color, size, and actions the spoonbilled sandpiper closely resembles the Eastern least stint (Pisobia minuta ruficollis), the marked similarity between them resulting in both the author and his fellow collector W. S. Brooks, failing to distinguish between the two species until June 20, after we had been among them for some days. Although the spatulate tip of this bird's bill is very noticeable when viewed from directly above or below, it is not a character which can be advantageously used to identify the species in the field, for the simple reason that in nearly all close views of the living bird only lateral or frontal aspects of the bill are obtained. Even when a bird was feeding, and the bill was observed under the most favorable conditions, the peculiar shape was not nearly as conspicuous as one would expect. In the author's experience, the most reliable method of identifying the bird in the field was by noting the glint of light that was reflected from the broad tip of the upper mandible when the sunlight struck the bill at a certain angle. Even in flight the bird could often be identified by this faint beam of reflected light. We found that the sandpiper had a decided preference for the grassy margins of fresh-water ponds, while single birds were frequently found feeding along the algae-bordered rims of tundra pools. Sandy lagoons where rivers entered the bay were favored by them as well.
Fall.—The same writer outlines the fall migration, based on birds in the British Museum, as follows:
An adult male, still in summer plumage, was taken August 8, at the mouth of the Amur River in southwestern Russia. An immature was secured on October 8 at Hakodadi (Hakodate), Japan, while an adult female was collected at Rangoon, India, on December 1.
Winter.—In their winter home in India, according to Doctor Nelson (1887) "these birds frequent the muddy flats at the mouths of rivers, sand bars, and the seashore, where, with the various species of Tringa, they always find an abundant harvest of food deposited by the receding tide."