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

BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 4?
Lake Junin, Peru. Comparison of a skin from Santiago, Chile, with
two from Argentina shows no differences that may not be ascribed
to individual variation. Specimens from the Falkland Islands, the
type locality, are not available to me at present.
On December 15, 1920, as I came down from Carhue, Province of
Buenos Aires, to the shore of Lago Epiqu«n, I made out the forms
of thousands of small white-breasted birds resting on the surface of
the water. On closer approach I found that they were grebes of the
present species swimming, preening, resting, or feeding in loose
flocks and bands that extended down the lake until lost to view in a
shimmering heat haze that danced over the water. From where I
rested on a small hillock overlooking the barren shores of the saline
lake (similar in formation and salinity of water to Great Salt
or Owens Lakes in the United States) fully 10,000 grebes were in
sight, while the number on the entire expanse of the lake, a body 35
kilometers long by 20 kilometers wide, must have been immense. All
were in full plumage and at a short distance appeared entirely white.
Though the majority were quiet, mating activities were carried on
in a few areas. Pairs or occasional parties of five or six individuals
partly rose on the surface, and with sides touching, dashed off across
the water for 10 or 12 meters. Usually as they stopped one, or more
in case of a small flock, rose, and with extended neck and fluttering
wings, splattered off for a short distance alone. Pairs approached
one another with the posterior portion of the body lowered and
breast raised, frequently to remain with breasts opposed, as they
turned and pressed against one another, for a minute or more. At
such times the breast feathers were expanded laterally, so that the
birds appeared large. A call note resembling tick tick, given in an
excited tone, was heard constantly. On the whole, the actions of the
birds reminded me of the American eared grebe {GolyTnbus nigri-
collis calif07viicus) , but were more subdued. It is possible that they
became more active a little later in the season, as not more than 5 per
cent as yet felt the mating impulse. It is presumed that the species
may nest in lakes in the mountains. E. Budin, of Tucuman, accord-
ing to Hartert and Venturi,^* found the species nesting in a lake in
the Cumbres de Calchaqui at an altitude of 4,300 meters. The
birds were in all probability attracted to Lago Epiquen by the abundant
food available in the form of brine shrimp {Artemia, species),
but would not remain since the heavy, saline water and lack of aquatic
vegetation were not suitable for breeding colonies.
In early morning flocks swam up into the mouth of an arroyo
where fresh water entered the lake, and here on December 15 I
secured two and on December 16 another. These birds were easily
^ Nov. Zool., vol. 16, December, 1909, p. 256.