220 U.S. NATIONAL MUSEUM BULLETIN 233 



Chapman (1928, pp. 152-154) and Skutch (1954, pp. 298, 318-319) 

 have described something of the host relationship of the giant cow- 

 bird with two of its usual victims. Here we have a situation far more 

 tense and militant than in the smaller cowbirds. Writing of the 

 Montezuma oropendola, Skutch summarized his notes as follows: 

 "The Giant Cowbird who lays in an oropendola's nest meets far more 

 opposition than the parasitic birds of other species which lay their eggs 

 in the nests of small birds which breed in isolated pairs. The Giant 

 Cowbird that fuially succeeds in laying in an oropendola's nest must 

 not only dodge the watchful oropendolas of both sexes, but sometimes 

 she must also outwit jealous rivals of her own species, each eager to 

 drop her own eggs into the newly finished nest and ready to drive 

 away another cowbird who attempts to get ahead of her. It costs the 

 cowbirds so much effort to foist their eggs on the oropendolas that I 

 suspect that it would involve very little more labor for them to build 

 some simple nest and rear their own young. 



"Had the oropendolas made a concerted attack upon these unbidden 

 guests, they might have driven them permanently from the nest tree; 

 but they are mild mannered birds and seemed to be content merely to 

 prevent entry of the cowbirds into then- nests . . . ." 



Skutch once saw a giant cowbird enter the nest of a Montezuma 

 oropendola. A few minutes later he saw an oropendola emerge, carry- 

 ing a giant cowbird egg in her bill. She dropped the egg, which 

 landed on the ground, unbroken by a fall of some 80 feet, Skutch 

 was able to measure it and found it agreed with published dimensions 

 of eggs of this parasite. 



All oropendolas are not as discerning or as hostile as this one, and 

 the species does at times accept the strange egg and rears the young 

 parasite. 



Studying Wagler's oropendola, Chapman concluded that these 

 birds appear to recognize the giant cowbird as an enemy "not 

 only when she seeks to enter a nest, but when, early in the nesting- 

 season, she enters the nest tree. Not alone the bird whose nest is 

 threatened but other birds in the same group, and also from other 

 groups, join in attacking her; while Legatus assails at times with more 

 zeal than Zahrynchus." It may be added here that Legatus is a small 

 flycatcher that usurps the nests of the much larger oropendolas, and 

 then breeds in them. This is the case of a nest robber driving away 

 a nest parasite even while the nest is still in the possession of its 

 original builder and owner. 



The above observations on the hostility toward the giant cowbird 

 shown by these colonial nesting icterids reminds one of the comparable 

 situation that occurs between the brown-headed cowbird and the 

 redwinged blackbirds, which nest in rather closely integrated groups 



