• Weatherhead, Patrick J.


Studies aimed at determining why female birds often produce offspring sired by males other than their social mates generally compare traits of social and genetic mates. Here I examine paternity patterns in nests of the same female red–winged blackbirds (Agelaius phoeniceus) in successive breeding seasons. Returning females preferentially selected their former social mates as their new social mates when those males were present. However, paternity patterns were much less consistent. A female's behaviour (faithful versus unfaithful) in one year did not predict her behaviour the following year. Females unfaithful in successive years did not prefer the same extra–pair males. Females unfaithful in one year that switched social mates the next year did not preferentially choose their former extra–pair mates as their new social mates. By switching genetic mates, females did not generally improve the quality of their mates. These results, together with previous analyses, suggest that female blackbirds in this population have little control over extra–pair mating. Although females may benefit from extra–pair mating because extra–pair males are generally longer lived, paternity patterns in this population are not consistent with extra–pair mating being part of a finely tuned female reproductive strategy.


Nests located, females mist-netted, colour-banded, blood sample. Nestlings banded and blood sampled