Parental care and mating behaviour of polyandrous dunnocks Prunella modularis related to paternity by DNA fingerprinting

INDIVIDUALS are often assumed to behave so as to maximize their reproductive success1 but unambiguous determination of parentage is difficult, especially in species with complex social systems where a female may mate with several males and where there may also be intraspecific brood parasitism^2,4. Even in apparently monogamous species, extra-pair paternity can be common^5,7. DNA fingerprinting^8,11 promises to revolutionize field studies by providing a powerful method for determining paternity and maternity¹². Here we use this technique to link observations of mating behaviour and parental care with precise measurements of reproductive success. We show that in the dunnock Prunella modularis, a small passerine bird with a variable mating system^13,14, males do not discriminate between their own young and those of another male in multiply-sired broods. Nevertheless, they increase their own reproductive success by feeding offspring in relation to their access to the female during the mating period, which is a good predictor of paternity.