HOST RELATIONS OF PARASITIC COWBIRDS 205 



Hoy noted a peculiar situation for which, with present information, 

 no explanation can be advanced. Asthenes baeri and another spine- 

 tail, Phacellodomus rufifrons sincipitalis, are both common locally; 

 both build similar types of nests in similar places, the nests of the 

 latter differing from those of the former only in their somewhat larger 

 size. Despite the similarity, the shiny cowbird parasitizes the former 

 of these two and apparently does not show any interest in the latter. 

 Yet the nonparasitic bay-winged cowbird, Molothrus badius, uses with 

 equal frequency old nests of both of these spinetails for its own 

 breeding site. 



Firewood -gatherer 



Anumbius anumbi (Vieillot) 



To the single earlier record Usted by me (1938, p. 43), may be 

 added one more. G. Harrison (1950, p. 6) mentions an egg of the 

 shiny cowbird taken with a set of eggs of the firewood-gatherer. 

 Apparently it was collected in Argentina, which was the locality in the 

 earlier case. The large stick nests of this and other woodhewers are 

 not particularly favored by the shiny cowbird. 



White -naped Ant Shrike 



Sakesphorus bernardi (Lesson) 



The white-naped ant shrike is a recent addition to the recorded 

 hosts of the shiny cowbird, which was reported in this capacity from 

 the Santa Elena peninsula of southwestern Ecuador by Marchant 

 (1958, p. 384; 1960, p. 369, 584). The typical race of the host and the 

 race A/.6. aequatorialis of the parasite are involved here. Marchant 

 observed four parasitized nests, of which only one produced a young 

 cowbird; two were total losses, with their included eggs, and in a third 

 the cowbird egg disappeared before the host young was well along in 

 its development. 



Gray Pepoaza 



Xolmis cinerea (Vieillot) 



This flycatcher has been found to be parasitized in the state of 

 Minas Geraes, Brazil, by the local race of the shiny cowbird {M.b. 

 bonariensis) . The report was made by Chagas (in litt.). There are 

 no previous records of this bird as a cowbird victim. 



Widow Pepoaza 

 Xolmis irupero (Vieillot) 



Recently Hoy (mss., 1961) near Salta, northwestern Argentina, 

 found that this flycatcher, which breeds in old nests of the ovenbird, 

 Furnarius rujus, is parasitized regularly by the shiny cowbird. Judg- 

 ing from his experience of finding broken cowbird egg shells on 

 the ground beneath such nests, he concluded that Xolmis showed a 



