Extra-pair paternity is not driven by inbreeding avoidance and does not affect provisioning rates in a cooperatively breeding bird, the noisy miner (Manorina melanocephala)

In many socially monogamous bird species, both sexes regularly engage in mating outside their pair bond. While the benefits of extra-pair (EP) mating behavior are clear and well established for males, such as an increase in the number of sired offspring, the benefits of EP mating behavior to females are less clear. A dominant theory for the incidence of EP mating is that socially monogamous females can improve the genetic quality of their offspring and avoid the costs of inbreeding through EP mating. In addition, in cooperatively breeding species, the theory of ‘parental care’, predicts that females obtain additional help for their offspring through extra-pair matings. Here, we examined evidence for both the inbreeding avoidance and parental care hypotheses in the cooperatively breeding noisy miner (Manorina melanocephala). Overall, EP mating occurred in 27% of broods, with 14% of offspring sired by males other than the identified pair-bonded male. There was a strong tendency to avoid p...