Male rank, female breeding synchrony, and patterns of paternity in the boat-tailed grackle

Species in which males directly defend groups of breeding femalesoftenhave extreme skew in observed male mating success. Inonly a few species,however, has a corresponding skew in fertilizationsuccess been confirmed.Furthermore, the ecological and socialfactors contributing to variation infertilization success needinvestigation. This study examined competition formates andpaternity in the boat-tailed grackle (Quiscalus major).Observationsat colonies of nesting females revealed that the toprankingoralpha males performed more than 70% of the copulations. DNAfingerprintingindicated that alpha males sired less than 40%of nestlings. Nevertheless,analysis of band-sharing scoresamong nestlings from different nests suggestedthat alpha malessired more than three times as many offspring as any otherindividualmale. Because few nestlings were sired by the nonalpha malesthatassociated with colonies, females must have mated withother males while ontrips away from colonies. Analysis of paternitywithin broods revealed that atleast half of all females hadtheir brood fertilized by more than one male.Alpha males' successat fertilizing eggs did not vary with the number ofsimultaneouslyreceptive females within a colony. Our results suggest thatmaleand female behavior in female-defense polygyny results fromcomplexcoevolution of the sexes.