Mating system and reproductive skew in a communally breeding cuckoo: Hard-working males do not sire more young

In communally breeding animal societies, theory predicts that a male's investment in parental care should be correlated with his share of paternity in the mixed brood. Here I test this hypothesis in the greater ani, Crotophaga major, a Neotropical cuckoo that nests in groups composed of two to three unrelated, behaviourally monogamous pairs. Each group constructs a single nest in which all of the females lay eggs, and all group members participate in rearing the joint clutch. Previous work has shown that parental investment among males is unequal: just one male in the group performs all nocturnal incubation, and the same male also plays a greater role in diurnal incubation and nest defence. I used parentage and sibling analysis of 357 greater ani nestlings in 53 clutches to investigate genetic mating patterns and the distribution of reproduction within communal groups. Contrary to predictions, male reproductive skew was negligible and nocturnally incubating males did not sire significantly more nestlings than did non-nocturnal incubators. Approximately 75-80% of nestlings were produced by socially monogamous pairs, 12-18% by extrapair fertilizations within the same breeding group, and 3-5% by extrapair fertilizations outside the breeding group. There was no difference in the frequency of extrapair paternity between nocturnally incubating and non-nocturnally incubating males. Compared to other cooperative avian societies, the division of reproduction in greater ani breeding groups is unusually egalitarian, despite marked inequalities in male parental care.