Record Details

Robinson, S. K.
Foraging ecology and host relationships of giant cowbirds in southeastern Peru
Wilson Bulletin
Journal Article
Parque Nacional del Manu animals invertebrates arthropods insects chordates vertebrates birds animal behavior parasites Cocha Cashu feeding Giant Cowbirds Scaphidura oryzivora single-species study small spatial scales Russet-backed Oropendolas Psarocolius angustifrons Yellow-rumped Caciques Cacicus cela Madre de Dios Bibliography
I studied the foraging ecology and host relations of a population of brood parasitic Giant Cowbirds (Scaphidura oryzivora) in the undisturbed Manu National Park of Amazonian Peru. Giant Cowbirds foaged mostly along rivers and lakes where they searched for arthropods, fruit, and nectar. Male cowbirds sometimes foraged on the backs of mammals on which they captured biting flies. The two potential host species, the Russet-backed Oropendola (Psarocolius angustifrons) and Yellow-rumped Cacique (Cacicus cela) defended their colonies against cowbird parasitism, regardless of colony location. Giant Cowbirds concentrated most of their visits on oropendola nests, which were sometimes left untended when the colony members were foraging together in a flock away from the colony. Yellow-rumped Caciques, however, seldom left their colonies untended and no cowbirds were known to fledge from cacique nests during the five years of the study. This situation differs markedly from that reported by Smith (1968, 1979, 1980) in Panama where Giant Cowbirds parasitized both oropendolas and caciques, and at least some hosts did not chase cowbirds aways from their nests. I argue that the major difference between the two study areas is that in Peru, both caciques and oropendolas generally raise only a single young, which means that there can be no advantage to being parasitized as there is in Panama.
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