196 U.S. NATIONAL MUSEUM BULLETIN 233 



Rio de Janeiro constitute strong evidence that a number of the female 

 cowbirds they studied were restricted to one host species, the chingolo 

 sparrow, Zonotrichia capensis, even though other potential victims 

 nesting in the area were seasonally and ecologically available. It is 

 possible that something of this sort may be involved in the case of the 

 wren Troglodytes musculus in Surinam. There, however, the evidence 

 is as yet less explicit and less impressive. 



Destruction of Host Eggs by Parasite 



As in the case with many parasitic birds, the shiny cowbird destroys 

 many eggs of its hosts before, after, or at the time of the laying of its 

 own eggs in their nests. In the species, however, there is some evi- 

 dence that the habit of deliberately puncturing eggs with its biU has 

 become established beyond any immediate or even approximate 

 correlation with its own ovulation. In Salta, northwestern Argen- 

 tina, Hoy (mss., 1961) found that this cowbird continued to destroy 

 eggs of other birds long after its own breeding season. Not only 

 was the habit unduly protracted, but also it was continued with 

 undiminished frequency. Egg destruction was not limited to fe- 

 male cowbu'ds but was indulged in by males as well. On Janu- 

 ary 26 Hoy was watching the nest of a tanager, Thraupis bonariensis, 

 which nest contained no cowbird eggs and 3 tanager eggs. When 

 the incubating bird left the nest for a moment, a male shiny cowbird 

 suddenly appeared, went directly to the nest and immediately de- 

 stroyed aU 3 eggs by pecking holes in them. 



It is weU established that egg-pecking is far from universal; many 

 parasitized nests show no such activities. The situation is thus 

 similar to that of the brown-headed cowbird, with the important 

 difference that, in the latter case, egg-pecking is restricted to nests 

 already parasitized or about to be parasitized — and only to such 

 nests. In other words, there is a close correlation between egg-laying 

 and egg-pecking in the bro^vn-headed species but not in the shiny 

 cowbird. 



Hosts Known To Have Reared Young of the Parasite 



The present host catalog is heavily weighted with records of eggs 

 which were seen and collected instead of being allowed to hatch and 

 thus afford an opportunity to watch the young develop. This 

 necessarily increases the number of cases wherein we have no definite 

 information that the host could and would rear the parasitic young, 

 but the absence of such data cannot be taken as meaningful. Of the 

 146 species in our present list, the 26 listed below have been reported as 



