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

BIBDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 303
more restricted, so that instead of seven outer primaries that are
nearly white the number is reduced to six, as the outer web of the
fourth primary is extensively black. The black on the others is
also increased both on the outer web and at the tip. The wing varies
from 92 to 93.6 mm. (average of three specimens, 92.7 mm.). These
show a distinct approach to andina, but are nearer perspiciUata.
Finally, at Zapala and from the region south of the Rio Negro come
specimens in which the black on the outer webs of the primaries
may extend 5 or 6 mm. beyond the primary coverts, in which the
shafts are black and the distal dark patch extensive. The wing in
these ranges from 90.1 to 96.2 mm. (average of four specimens,
92.9 mm.). Though the white may be somewhat more extensive
than in some from Chile, these seem best referred to andina. In
these the white in the closed wing appeared streaked with black
owing to the extent of the dark markings on the outer webs of the
primaries.
A male taken at San Vicente, Uruguay, January 27, is molting
the body feathers, while in three from Timuyan, Mendoza (March
21 to 28), the outer primaries are being renewed.
Following are the localities and dates when this flycatcher was
recorded : Berazategui, Buenos Aires, June 29, 1920 ; Resistencia,
Chaco, July 9 and 10; Las Palmas, Chaco, July 13 to August 1;
Riacho Pilaga, Formosa, August 8 to 20 ; Formosa, Formosa, August
23; Puerto Pinasco, Paraguay, September 3; Kilometer 80, west of
Puerto Pinasco, September 17; Dolores, Buenos Aires, October 21;
Lavalle, Buenos Aires, October 23 to November 15; General Roca,
Rio Negro, November 23 to December 3; Ingeniero White, Buenos
Aires, December 13; Carrasco, Uruguay, January 9 and 16, 1921;
La Paloma, Rocha, January 23; San Vicente, Rocha, January 27 to
February 2 ; Lazcano, Rocha, February 5 to 9 ; Potrerillos, Mendoza,
March 16 ; Tunuyan, Mendoza, March 22 to 29.
The silverbill is restricted in its haunts to the vicinity of water.
Though common in the Chaco north to the Rio Pilcomayo, it seemed
rare or local beyond. In the pampas it was locally common in
northern Buenos Aires, but was not detected in the regions that I
visited near Guamini or Carhue. In northern Rio Negro it frequented
the vicinity of streams, but was also common in the irrigated alfalfa
fields, haunts that will enable the bird to extend its range, as culti-
vation, through enlarged irrigation projects, increases in the arid
sections of northern Patagonia and western Argentina. In the
Province of Mendoza, where part of the birds noted may have been
migrant from the south, the species was found along streams and
irrigating ditches, on one occasion at an altitude of 1,500 meters in
the vallev at Potrerillos.