BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 155 



Baird's sandpiper from the pectoral, since P. nielanotos has the tip of 

 the bill heavily pitted. The appearance of the bill Avill thus sepa- 

 rate these two readily where size or the color of the rump and upper 

 tail coverts are not sufficiently distinct. 



The white-rumped sandpiper was the most abundant of the 

 migrant shore birds in the regions visited in southern South Amer- 

 ica. 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 appearence of the 

 ovaries. The southward 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 encoun- 

 tered 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 200 were observed in the bay at Ingeniero "V^Hiite, 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, 



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 move- 



