Social mating system and reproductive success in house wrens

Current models explaining the establishment and maintenance of social monogamy and polygyny within avian populations typically assume that the reproductive success of polygynous males exceeds that of monogamous males. This assumption is almost always supported when the number of fledglings or recruits to future breeding populations is used to measure adult reproductive success. However, recent studies using DNA markers indicate that simple counts of fledglings or recruits may be a poor estimator of the number of nestlings sired by the social father. In this paper, we compare the number of genetic offspring produced by socially monogamous and polygynous house wren (Troglodytes aedon) males in nests at which they were the social father. Polygynous males did, in fact, sire more nestlings in their own nests than did monogamous males. Moreover, although we have not identified the sires of extrapair nestlings, we document that even when all extrapair nestlings in this population are hypothetically assigned to monogamous males, the total reproductive success of polygynous males exceeds that of monogamous males. These results and those of several other recent studies are consistent with the assumption that polygynous males produce more offspring than monogamous males.