Sexual dimorphism and parental care in the Yellow-winged Blackbird (Agelaius thilius)

VIVIANA MASSONI; VERONICA LOETTI; JUAN CARLOS REBOREDA

ORNITOLOGIA NEOTROPICAL

Neotropical Ornithological Society

Lugar: Montreal, Quebec, Canada; Año: 2005 vol. 16 p. 551 - 555

1075-4377

Yellow-winged blackbirds (Agelaius thilius) show strong sexual dichromatism and have been reported as being size monomorphic, strictly monogamous and with somewhat female-biased food provisioning of young. Given their external similarity with Red-winged Blackbirds and their marsh-nesting habits, a polygynous species with female biased parental care, we investigated the Yellow-winged Blackbird sexual size dimorphism and the type and amount of parental care provided by each sex. Males are, indeed, significantly heavier and bigger than females, and the extent of size dimorphism ranged between 7 and 20 %. However, males' and females' contributions to parental care in the nest were not different, and we found nests attended by single males, an event consistent with monogamy, but also by single females, as may be common in polygynous systems.