A nest containing four eggs was found on a grassy hummock on the tundra bordering the lake on June 16. Many were subsequently found. The nest is merely a shallow depression on the crown of a tussock of grass and mosses a few inches above the surrounding mud and water of the tundra. It is sparingly lined with blades of old grass and dead leaves of the dwarf arctic willow. Some are lined exclusively with the dried, oval leaves of Salix herbacea. According to collecting data, both sexes arrive together, with the female almost, if not quite, ready for immediate reproduction, as evidenced by the condition of the ovaries. The nest of four eggs found on June 16 was but four days after the first observed arrivals of the species.
The female upon one's approach plays the familiar artifice of simulating a prostrated condition, limping and dragging herself along the ground in an effort to attract one's attention from the nest. In this they are bold and fearless; and when one sits beside the nest they will frequently run up to within a foot or less of the observer. In photographing nests from a distance of only a few feet, the female will often return to her eggs while one's head is under the dark cloth adjusting the focus. One was so devoted to her eggs that she would run up and peck at my fingers and run over my hand as I extended it toward the nest. This species, when one approaches the nest, usually leaves it when one is 20 to 25 yards distant and runs along the ground, either directly toward the intruder or a little to one side. Because of its remarkable similarity to the covering of the tundra at this time, this first movement often escapes one, and consequently when the bird is first observed fluttering along the ground one naturally imagines himself near the nest, when, in reality, it may be 20 or 30 yards away. This ruse is a clever one, and no doubt would often save the nest from violation. The nests are easily found by retiring and watching the female with the glasses. They usually return to the nest with little artifice or delay; in fact, often within two or three minutes. The above procedure is not an invariable practice, as one female I knew would flush directly from the nest to begin her tactics only when there was danger of the nest being actually trodden upon.
Eggs.—The four eggs usually laid by the white-rumped sandpiper are ovate pyriform in shape; all that I have seen are uniform in shape and have characteristic colors and markings. One of the two sets in the United States National Museum has a "deep olive buff" ground color, and the eggs are heavily blotched about the larger end, sparingly spotted elsewhere with "wood brown," "warm sepia," and "benzo brown," and with a few underlying spots of various shades of "brownish drab"; an egg from this set is well figured by Frank Poynting (1895). The other set differs from this one in having the ground color lighter, "olive buff," and the spots finer, more scrawly, and lighter in color; the underlying drab markings are also more numerous.
There is also a set of four eggs in the Thayer collection, taken with the parent bird by Alfred H. Anderson on Taylor Island, Victoria Land, July 7, 1919. These eggs are much like the egg figured by Mr. Poynting, except that in one or two of the eggs the ground color is more greenish.
One of the three sets taken by J. Dewey Soper on Baffin Island looks much like a miniature set of long-billed curlew's eggs. In three of the eggs the ground color is "mignonette green," covered with small spots, more thickly at the larger end, of "bister" and "snuff brown"; the other has a "deep lichen green" ground color and is irregularly blotched near the larger end, finely speckled elsewhere with "bister" and "brownish drab."
The measurements of 34 eggs average 33.7 by 24 millimeters; the eggs showing the four extremes measure 36.1 by 23.6, 34.2 by 27.7, 31.5 by 23.5, and 35 by 22.8 millimeters.
Young.—Mr. Soper's notes on the young are as follows:
The first juveniles, about a day old, were seen and collected on July 11. They were exceedingly active, a good example of precocial young. These were ashy below, buffy above, with black markings, and the down over the lower back and rump tipped with small spots of white. This species is much more demonstrative and less artful in the concealment of young than Baird's sandpiper. The adults come within a few feet of the intruder, and by their action advertise much more clearly the position of the young. The parent birds keep up a continual fine twittering cry of alarm, the female louder and more pronounced. The male comes on the scene only at intervals with a mouse-like squeaking note. The young are adepts in the art of concealment, "freezing" flat to the ground with warning notes from the adults. They will lie in this fashion as though dead until actually picked up in the hand. When they realize the game is up they then become wild and frantically struggle to escape. When allowed to do so they will run rapidly away and either hide again or attempt to reach the mother bird, whose frantic cries come from but a few yards away.
A young white rump about two-thirds grown and almost on the point of flight was captured on August 1. Others seen a few days later on the shore of Kuksunittuk Bay were capable of short flights. As an experiment, I tried several times to keep individual young alive at my base tent on the Takuirbing River, but they invariably died within about 24 hours regardless of the best care.