At Guamini, Buenos Aires, from March 3 to 8, white-rumped sandpipers were encountered in northward migration from a winter range in Patagonia. The species was fairly common on March 3 and increased greatly in abundance on the two days that followed. The northward journey was apparently as concerted as the movement that carried the birds southward, as on March 6 there was a noticeable decrease in their numbers, and by March 8, though the birds were still common, the bulk of individuals had passed. They arrived in flocks from the southward, often of several hundred individuals, that whirled in and circled back and forth along the lake shore to decoy to birds feeding on the strand or to rise again and continue swiftly northward. Those that paused kept up a busy search for food along the muddy beaches in or near shallow water, or in company with little parties of buff-breasted sandpipers on the drier alkaline flats back of the shore line. In early morning they were especially active and were in continual movement. Occasionally they worked out into comparatively deep water where in feeding it is necessary to immerse the head over the eyes nearly to the ear openings. When disturbed flocks rose with soft notes that resembled _tseet tseet_ or _tseup_ to circle to new feeding grounds on the lake shore. The spring migration route is apparently northward along the Atlantic coast of South America and through the West Indies to the United States. Only a few migrate along our Atlantic coast, as the main flight is northward through the interior, during May and the first few days of June. Many reach their breeding grounds before the end of May. _Courtship._--Doctor Wetmore (1926) gives an attractive account of what seems to be a beginning of courtship in Argentina; he writes: