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BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 285
Kidgway has recognized the genus Rhopochares of Cabanis and
Heine for the present group, but I have preferred to use the broader
generic term for it.
THAMNOPHILUS GILVIGASTER GILVIGASTER Pelzeln
Thamnophilus gilvigaster " Temminck " Pelzeln, Ornith. Brasiliens,
1868, p. 76. (Curytiba, Parana, Brazil.)
The male of the common ant bird of Uruguay differs from that
of northern Argentina in having the under tail coverts and flanks
darker buff, and the darker gray of the breast extended back to
the upper abdomen. Females likewise share the darker color of
the underparts so that both sexes may be distinguished at a glance
from dineUi'i. Doctor Hellmayr^* has considered the buff-bellied
ant birds of southern distribution as subspecies of Thamnophilus
caemlescens of Paraguay. With all due respect for the weight
of Doctor Hellmayr's opinion in such matters, I am not now prepared
to accept this in view of the greater difference in color
between the sexes in caerulescens. Although gilvigaster belongs
in the same group as caerulescens, and apparently occupies a con-
tiguous range, intergradation between the two does not seem to
have been proven, Thaiiuiophilus ochrus Oberholser is the female
of T. caerulescens, as is shown by examination of the type. In the
specimens that I have seen, gilvigaster is readily told from Thamno-
philus caerulescens Vieillot by the buff on the posterior portion of
the body and by its slightly larger bill.
Males were collected along the Rio Cebollati, near Lazcano,
Uruguay, on February 5 and 8, 1921, and an immature female on
February 5. An immature male was shot at Rio Negro, Uruguay,
on Februar}^ 17, and an adult female on February 19. The latter
specimens are fully as dark as those from eastern Uruguay and
show no intergradation toward the paler Argentine form. Aplin^^
has recorded a bird of this genus from the thickets along the
Arroyo Grande (a tributary of the Rio Negro) near Santa Elena,
but I failed to note it at San Vicente near the coast of southeastern
Uruguay. In its distribution in Uruguay this bird from its thickethaunting
habit would of necessity follow the courses of streams.
These birds were common near Lazcano, from February 5 to 8,
and in the vicinity of Rio Negro, from February 14 to 19, On
both the Rio Cebollati and Rio Negro they inhabited dense, heavy
growth near the streams where they moved about with jerldng
tails, or occasionally perched quietly, twitching the tail at intervals.
They showed considerable curiosity at strange sounds, and came
about to peer at me, sometimes within 3 or 4 feet of my face,
" Nov. Zool., vol. 28, May, 1921, p. 199, and Field Mus. Nat. Hist., Zool. ser., vol, 13,
pt. 3, Nov. 20, 1914, p. 102.
"Ibis, 1894, p. 185.
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