Ardea
Official journal of the Netherlands Ornithologists' Union

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Fraga R.M. (1992) Biparental care in Bay-winged Cowbirds Molothrus badius. ARDEA 80 (3): 389-393
Patterns of biparental care were investigated in the Bay-winged Cowbird Molothrus badius, an icterine with slight size dimorphism (6.2% by mass), dispersed nesting and cooperative breeding. Males seldom built nests and did not incubate, but spent more time near the nest in daytime than females. Because of nest losses most females produced two or three clutches per season, representing 42-92% of their body mass. Both parent provisioned nestling at equal rates, and the variance in feeding rates by males did not exceed that of females. Males performed most attacks on brood parasites and avian predators, starting the nest defence well before egg-laying. The basic roles of the sexes are consistent with data reported from other nesting icterines, and the male contribution to nesting is among the highest reported for this taxonomic group.


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