HOST RELATIONS OF PARASITIC COWBIRDS 221 



in cattail swamps. In the latter host-parasite relationship, the 

 parasite is successful only, or chiefly, with those redwings which nest 

 at wider intervals in bushes or at the periphery of a colony. 



The pugnacity and persistence often displayed by the giant cowbird 

 when attempting to gain entry mto the nests of its intended victims 

 is of some interest. This parasite is related to the bronzed cowbird 

 and, more remotely, to the screaming cowbird, a species which is also 

 quite pugnacious and resolute when about to enter a nest. The 

 shiny and the brown-headed cowbirds are more timid and are more 

 apt to sneak in while the owners are absent. 



The number of eggs laid by a giant cowbird in any one nest seems 

 to be usually 1 or 2. Schultz, as reported by Kuschel (1896, p. 

 585), recorded as many as 6 eggs of the giant cowbird in a single 

 nest of the yellow-rumped cacique near Para, Brazil, but some doubt 

 may be attached to this statement, as Kuschel's description of the 

 eggs, which are supposed to be those of giant cowbirds, do not agree 

 very closely with others subsequently collected. 



Many years ago in Brazil, Goeldi (1894, 1897) found that the young 

 giant cowbird did not starve out or otherwise elimmate a nest-mate 

 of the host's species (at least in the case of Xanthornus decumanus), 

 but that the two grew up together. Crandall (1914, p. 338, 342) 

 found a parasitized nest of each of the two chief host species in Costa 

 Rica, Zarhynchus wagleri and Gymnostinops montezuma, each of 

 which contained a nestling giant cowbird together with one of the 

 host young. In both instances the disparity in appearance of the 

 parasite and its nest-mate was very striking, but in both cases the 

 adult fosterers attended them equally. In British Guiana, Young 

 (1929, p. 256) also noted that the nestling of the giant cowbird and 

 that of its host developed together without obvious hostility. Skutch 

 noted that he never found fledgling giant cowbirds in flocks of oropen- 

 dolas but only with an individual foster parent. He was led to ask, 

 ". . . can it be that the other oropendolas will not tolerate the pres- 

 ence of these intruders and that the foster mother prefers to lead a 

 lonely life along with her foster young rather than desert it?" 



In British Guiana, Young (1929, pp. 251-253) concluded that the 

 giant cowbirds seemed to lay 2 eggs in nests of the crested oropen- 

 dola, Xanthornus decumanus, and in nests of the yellow-rumped 

 cacique, Cacicus cela, but he did not make it clear whether his evidence 

 pointed to the same hen laying 2 eggs in each nest or to two individ- 

 uals depositing 1 each. He found the yellow-rumped cacique to be 

 imposed upon frequently and he noted that the young parasites grew 

 up together with, not at the expense of, theu* rightful nestmates. 

 Unlike Skutch's experience in Central America, Young saw flocks of 

 yellow-rumped caciques accompanied by both theu' own young and 



