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 pre- 

 pared 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, T haiiuiophilus 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 thicket- 

 haunting 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. 



54207—26 19 



