Nesting.—Comparatively little is known about the nesting habits of the stilt sandpiper. Roderick MacFarlane (1891) found it "fairly abundant on the shores of Franklin Bay, where a number of nests with eggs and young were discovered. It is, however, very rare in the interior, only one nest having been taken at Rendezvous Lake on the borders of the wooded country east of Fort Anderson." A nest with three eggs, found on June 22, 1863, is described in his notes as "near a small lake and composed of a few decayed leaves placed in a depression in the ground, partly concealed by a tuft of grass;" the female was flushed off the nest and shot. The nest found at Rendezvous Lake is not described, but one found at Franklin Bay, on July 6 or 8, 1865, containing four fresh eggs, was "a mere depression in the ground, lined with a few withered leaves and grasses."
Eggs.—Four eggs is probably the usual number laid by the stilt sandpiper. They are ovate pyriform in shape. The only eggs I have been able to locate are the three sets in the United States National Museum, collected by MacFarlane. J. H. Riley has kindly sent me descriptions and measurements of these. In the set of four eggs the ground color is "ivory yellow" with large irregular blotches and spots of two shades of "mummy brown," and a few rather large shell markings of "hair brown," the latter mostly towards the larger end. The spots and blotches are a little heavier towards the larger end, also, but in no sense do they form a ring. Another set of two eggs is similar, but the spots and blotches are much smaller, more numerous, and more evenly distributed over the surface; some of the "mummy brown" spots are even becoming scrawls. The third set of two eggs are like the set of four, except that the ground color is "pale olive buff" and the "mummy brown" blotches are on the average smaller. The measurements of these 7 eggs average 35.5 by 25.1 millimeters; the eggs showing the four extremes 36 by 25, 35 by 26, 35 by 25 and 36 by 24.5 millimeters.
Young.—Mr. McFarlane (1891) says: "On one occasion we could not help admiring the courage and ingenuity displayed by both parents in defense of their young, which resulted in saving two of the latter from capture."
Plumages.—In natal down the stilt sandpiper closely resembles several of the other species of tundra-nesting sandpipers. It can generally be recognized by its relatively longer legs and by its longer bill, with a broader tip. The head markings are also a little different. The forehead, cheeks, and throat are dirty white, with a broad, black, median stripe from bill to crown, another (loral) from bill to eye, and a short one (malar) below it. The crown, back, wings, thighs, and rump are variegated or marbled with black (predominating) and dull browns, "tawny" to "ochraceous tawny," and profusely dotted with dull white terminal down tufts; these dots form a distinct circle around the crown patch, below which the whitish sides of the head are marked with "ochraceous tawny." The lower throat is washed with pale buff, and the rest of the under parts are white.
In the juvenal plumage in August the head and neck are streaked with gray and whitish; the crown is dusky, with buffy edgings; the mantle is brownish black and dusky, with "tawny" edgings on the blackest feathers in the back and scapulars, and with pale buff or whitish edgings on the rest of the mantle and tertials; the under parts are white, suffused with pale buff on the throat, breast, and flanks; the wing coverts are edged with pale buff or whitish; the upper tail coverts are white and but little marked; the central tail feathers are dusky, edged with white, and the others are white, margined with dusky. This plumage is not worn long, for the postjuvenal molt of the body plumage begins late in August and lasts through September, producing a first-winter plumage. This is similar to the winter plumage of adults, but can be recognized by the juvenal wing coverts, some scapulars, and tertials.
I have been unable to trace the first prenuptial molt of young birds, which is probably accomplished in South America, nor have I been able to recognize a first nuptial plumage. Possibly young birds may not come north during their first spring.
Adults have a partial prenuptial molt in April and May, involving the body plumage, most of the scapulars, and some of the wing coverts and tertials. The complete postnuptial molt begins sometimes during the first week in July and sometimes not until the last of that month, and is completed in about two months, including the wings. A specimen taken in Argentina on September 21 had renewed the wings and practically all of the body plumage. In winter plumage the upper parts are brownish gray, with narrow, light edgings; the sides of the head and the under parts are white, with little or no barring; there is a dark streak through the eye, but no rusty on the head.
Food.—Audubon (1840) watched a flock of about 30 stilt sandpipers feeding, of which he writes:
I saw a flock of about 30 long-legged sandpipers alight within 10 steps of me, near the water. They immediately scattered, following the margin of the retiring and advancing waves, in search of food, which I could see them procure by probing the wet sand in the manner of curlews, that is, to the full length of their bill, holding it for a short time in the sand, as if engaging in sucking up what they found. In this way they continued feeding on an extended line of shore of about 30 yards, and it was pleasing to see the alacrity with which they simultaneously advanced and retreated, according to the motions of the water. In about three-quarters of an hour, during all which time I had watched them with attention, they removed a few yards beyond the highest wash of the waves, huddled close together, and began to plume and cleanse themselves. In the stomachs of several individuals I found small worms, minute shellfish, and vegetable substances, among which were the hard seeds of plants unknown to me.