Data from: 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 pairing
with genetically related individuals, with 86% of breeding pairs being
significantly less related to each other than the general population. The
occurrence of extra-pair paternity was independent of the degree of
relatedness between the pair. Provisioning patterns in relation to EP
mating was not consistent with the ‘parental care’ hypothesis and EP males
did not contribute to the care of broods. These results demonstrate that
in this system, there is no evidence that EP mating might function as a
mechanism to reduce the costs of inbreeding depression or to gain benefits
of extra helpers.