Bulletin - United States National Museum - si-pddr - Smithsonian ...

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 separate
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 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 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 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 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-