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

BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 273
scribed by Lillo as S. dineJUi.*^ The tips of the tail feathers are
rounded and do not display the acuminate points found in hudsoni
and anthoides, a condition that may change with age. Hellmayr*^
has indicated that S. lilloi is the bird described by Chapman ^^ from
above Tafi del Valle, Tucuman, as Siptornis punensis rufala.
The individual taken was flushed among tussock grass that cov-
ered an open slope at the summit of the cumbre, and was killed on
the wing. It appeared dark in color when in the air, with a distinct
reddish-brown band in the wings. A bird of similar appearance
that I flushed but did not secure in tussock grass on the highest
points near El Salto above Potrerillos, Mendoza, during March was
probably Siptornis anthoides.
SIPTORNIS HUDSONI (Sclater)
Synallaxis hudsoni, P. L. Sclater, Proc. Zool. Soc. London, 1874, p. 25.
(Conchitas, Buenos Aires.)
Hudson's spinetail in general coloration suggests a pipit, while
in attitude and habits it is strongly suggestive of the allied Anumhius.
It was encountered at only two localities in the Province of
Buenos Aires, first near Lavalle, Buenos Aires, where it was fairly
common in marshes on October 23 and November 6 and 9, 1920, and
a second time near Guamini, where, on March 8, 1921, I found three
in a dense patch of thistles and other weeds on the shore of the
Laguna del Monte. Near Lavalle the bird was partial to marshes
grown heavily with Juncus acutus, a sharply pointed rush that grew
in clumps with little runways between. The birds were shy and
secretive and were seldom seen until they darted out and flew
rather swiftly with undulating flight to new cover. When once
under shelter they crept rapidly away so that it was difficult in
many instances to flush them a second time. The light outer margins
of the tail showed prominently in flight. Occasionally one perched
quietly among dead rushes at the border of some lagoon.
On the evening of November 6, while setting a line of mouse traps
among hollows between the dunes south of Cape San Antonio, I
flushed one of these birds from the base of a clump of Juncus and
after careful search discovered a nest, a domed structure placed
directly on the ground in the base of the tussock of rush, with a
runway like that of some mouse leading into it. Never have I
seen the nest of a bird more completely concealed from any possible
view, and save for the chance that directed my hands to the base of
the clump in question, so that the female flew out almost in my
" Rev. Letr. Cienc. Soc. Tucuman, vol. 3, July, 1905, p. 53.
*- Arch. Naturg., vol. 85, November, 1920, p. 72.
*3Bull. Amer. Mus. Nat. Hist., vol. 41, Sept. 1, 1919, p. .'?28.