Farther south this species was encountered in abundance in its winter range on the pampa. Ten were recorded at Dolores, Buenos Aires, October 21, and from October 22 to November 15 the species was found in numbers on the coastal mud flats on the Bay of Samborombom. A few were seen at pools of water in the sand dunes below Cape San Antonio. Along the Rio Ajo white-rumped sandpipers were encountered in flocks of hundreds that came upstream to search the mud flats at low tide or were concentrated on bars at the mouth when the water was high. In early morning there was a steady flight of them passing to suitable feeding grounds. The birds flew swiftly, with soft notes, from 3 to 15 feet from the earth. In feeding they scattered out in little groups that covered the bare mud systematically. It was not unusual to record as many as 2,000 in a day. About two hundred were observed in the bay at Ingeniero White, the port of Bahia Blanca, on December 13, and at Carhue, Buenos Aires, from December 16 to 18, white-rumped sandpipers were noted in fair numbers on inundated ground back of the shore of Lake Epiquen or about fresh-water ponds on the pampa inland. None were found in Uruguay during February. Ernest Gibson (1920) says of this species, at Cape San Antonio, Buenos Aires: This is certainly our commonest wader, and is found everywhere in flocks, from, say, the end of October to the middle or end of March. The number in these gatherings is only restricted by the area of the feeding ground; hence, when large mud flats are available in the vicinity of our fresh or salt water lagunas and cangrejales, or at the subsidence of a flood, the flocks are sometimes of enormous size. The observer may see many acres of ground which look to be in continuous movement, the surface being alive with the restless throng of sandpipers running about and chasing each other, feeding, or taking constant short flights. DISTRIBUTION _Range._--North and South America; casual in Europe. _Breeding range._--Although the white-rumped sandpiper has been noted in summer from Wainwright, Alaska, east to southern Greenland (Julianshaab), the only places where eggs have been taken are Point Barrow, Alaska; Herschel Island, Yukon; Taylor Island, Victoria Land; Fort Anderson and Rendezvous Lake, Mackenzie; and the southeast shore of Lake Nettilling, Baffin Island. _Winter range._--North to Paraguay (Rio Pilcomayo and Rio Parana); and Uruguay (Montevideo). East to Uruguay (Montevideo); Argentina (La Plata, Cape San Antonio, Bahia Blanca, Rio Chubut, and Puerto San Julian); the Falkland Islands; and Tierra del Fuego. South to Tierra Fuego; and southern Chile (Straits of Magellan). West to Chile (Straits of Magellan and Santiago); and Paraguay (Rio Pilcomayo).