Mating strategies and extra-pair paternity in the Rock Sparrow (Petronia petronia)

Extra-pair paternity (EPP) is a widespread phenomenon in socially monogamous bird species, occurring when an individual mates outside its social pair bond. EPP is known for many different species, ranging from mammals, like White-handed Gibbons, to birds and including some invertebrates (Odontotaenius disjunctus). In this study, I investigate the association of EPP with brood desertion and parental effort in a Spanish population of Rock Sparrows (Petronia petronia). Both brood desertion and parental effort were assessed by behavioural data obtained through video recordings of each nest. In order to assess EPP, blood samples were collected from adults and nestlings of 26 broods, resulting in a total of 131 individuals. These were later genotyped using 10 microsatellites loci allowing the estimation of parentage and of the levels of EPP in the population. Results showed that 30.8% of the males deserted their brood, while no female desertion occurred (a possible scenario in the studied population). Genetic analysis confirmed the presence of EPP in the population: 4 nests out of 23 used for the molecular analysis show at least one extra-pair young. In particular, nests were EPP occurred were not more likely to be deserted. These findings support previous evidence that Rock Sparrows exhibit complex mating behaviours and sex-specific parental strategies, moreover they shed more light on this topic providing new information that could be useful for future research.