Shared paternity among non-relatives is a result of an egalitarian mating system in a communally breeding bird, the pukeko

With extra-pair paternity now known to be common among many species of birds, it is not surprising that males of most species exhibit behaviour that minimizes the risk of losing paternity. The most common form of paternity assurance is mate guarding whereby the male closely follows his mate during her fertile period and attempts to prevent other males from copulating with her. Even in communal or cooperative breeding species where two or more males collaborate in defending a breeding territory, mate guarding by the alpha male still occurs. Here we report that within communally breeding groups of pukeko (.Porphyrio porphyrio) dominant males do not guard their mates and rarely interrupt the copulations of unrelated rival males. This population of pukeko meets the conditions of a model that predicts that unrelated individuals who form breeding coalitions should interact in an egalitarian manner. DNA fingerprinting revealed a tendency for alpha males to father the majority of offspring in a brood, but frequent, uninterrupted copulations by subordinate birds assured that most males within the group had at least some paternity. Because the timing of ovulation is difficult to predict in female pukeko, individual males may be unable to estimate the proportion of eggs that they have fertilized, which could explain why most males participate more or less equally in parental care.