The species was encountered at Nettilling Lake, June 10, 1925, when a mated pair was flushed from a marshy upland near the Takuirbing River. The sexual organs in both were fully developed, the female being almost on the point of laying. By the 14th the species had become quite common. The males practised their vocal performance on the wing immediately upon arrival. They rise to a height of about 60 feet above the tundra and there they hover with rapidly beating wings giving utterance to their nuptial song in notes so weak that when a wind is blowing nothing may be heard of it even at comparatively close range. It is given in a very low tone and slow tempo; the notes are weak and inclined to be squeaky, with a weird dripping quality like the sound of water oozing and dropping in a small cavern. The species appears to flush silently. _Nesting._--Very little seems to be known and still less has been published about the nesting habits of the white-rumped sandpiper. In MacFarlane's notes I find brief records of seven nests found by his party on the barren grounds and Arctic coast of Canada, from 1862 to 1865. One nest was found on June 21, 1862, 50 miles east of Fort Anderson; the female and three eggs were taken; the nest consisted of a few leaves in a small hole in the ground near a small lake. Another found on June 29, 1863, on the barren grounds, is described as "a mere depression in the ground lined with a few decayed leaves"; the female and four eggs were taken. There is a set of four eggs in the Herbert Massey collection, taken with the parent bird by E. A. McIllhenny at Point Barrow, Alaska, on June 25, 1898; the nest is described as "a hollow in the moss on top of a ridge on the tundra, lined with dry grass and partly arched over." This is farther west than the species is supposed to breed, but there are several birds in the Philadelphia Academy of Sciences collected there in June, which are in full breeding plumage. Mr. Soper found a number of nests near Nettilling Lake, Baffin Island, on which he has sent me the following notes: 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.