190 BULLETIN 142, UNITED STATES NATIONAL MUSEUM 



plover, and sanderlings. They are not all asleep, however, for if 

 approached too closely, they all rise and whirl away in a vast shim- 

 mering cloud, flashing now white and now dark as they turn, and 

 settle on the beach again at no great distance. 



Winter. — August finds the white-rumped sandpiper migrating 

 along the coast of Brazil and it has been known to reach Cape Horn 

 as early as September 9. Doctor Wetmore (1926) writes: 



The white-rumped sandpiper was the most abundant of the migrant shore 

 birds in the regions visited in southern South America. The species was not 

 recorded until September 6, 1920, when it appeared in abundance in southward 

 migration on the lagoons at kilometer 80, west of Puerto Pinasco, Paraguay. 

 The first flocks from which specimens were taken were adult females, and 

 two taken on the date when they were first recorded had laid eggs a few 

 weeks previous as was shown by the appearance of the ovaries. The south- 

 ward migration came with a rush as the birds passed through the night as 

 witnessed by their calls. The flight continued until September 21, when a 

 dozen, the last seen here, were recorded. The birds circled about lagoons in 

 small compact flocks or walked along on muddy shores, where they fed with 

 head down, probing rapidly in the soft mud ; anything edible encountered was 

 seized and swallowed and the bird continued without delay in its search for 

 more. 



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 up- 

 stream 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 ob- 

 served 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 sand- 

 pipers 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 

 iound 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 

 laguuas and cangrejales, or at the subsidence of a flood, the flocks are some- 

 times 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. 



