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

270 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
is somewhat deeper brownish gray, less whitish below than others
that have been noted thus far. Immature birds in juvenal plumage
lack the colored throat patch and have the breast and foreneck
rather faintly vermiculated with dusky. The throat patch is assumed
early in the post-juvenal molt, save in those birds that do not
develop it. Its lack in certain individuals is an apparent retention
of a character of immaturity, as it may be held that the throat patch
has been a secondary acquirement. A single adult female secured
at Formosa, Formosa, on August 24, while somewhat duller and
darker on the breast than the average, is matched closely by some
individuals in the considerable series at hand from the south, and is
similar to an old specimen in the United States National Museum
collection from Santa Fe. I have not seen S. s. a-ffinis Berlepsch
from Tucuman, but, on the basis of Berlepsch's original description,
consider the Formosan specimen nearer to fiavogularis. It is pos-
sible that the one taken at Formosa represents a northern migrant,
as it Avas shot in winter.
Though recorded from northern Argentina, this spinetail was
most abundant in the semiarid regions of the south and west, where
it found a congenial home in low growths of bushes, particularly of
piquillin {Condalia lineata), atriplex, and a sort of grease wood
{Grahamia hracteafa) whose dense branches offered it safe cover.
In places, as near the coast at Bahia Blanca, the birds were abundant
and formed the dominant element among passerine species; at
other localities they were found sparingly or only in limited areas.
As they clamber around among the thorny twigs of dense bushes
these spinetails seem rather clumsy in their movements, and when
touched by thorns often fall with seeming awkwardness to one side.
In reality, however, they are expert in progression, and, in spite of
their seeming lack of skill, are working rapidly and surely through
difficult passages. At intervals one may pause, often on a concealed
perch near the ground, to sing a low, double-noted trill, tsee-ee-ee-ee
tsee-ee-ee-ee, that is given by both males and females. Occasionally
one may come up to sing from a more pretentious perch on the top
of a bush where it has a wider view of its chosen world. The habit
of song among females seems common in this group as I have noted
it among others of related genera. Flight, tilting and fairly rapid,
is practiced for short distances only, as the birds drop into safe cover
as soon as possible. In addition to their song they uttered chattering
scolding calls, especially during the breeding season and were considerably
excited by squeaking. It was not unusual to see them on
the ground, particularly under heavy cover.
A nest found near General Koca, on December 3, 1920, was placed
in a spiny bush among heavy branches about a meter from the