EXTRAPAIR PATERNITY INCREASES VARIABILITY INMALE REPRODUCTIVE SUCCESS IN THE CHESTNUT-SIDEDWARBLER (DENDROICA PENSYLVANICA), A SOCIALLYMONOGAMOUS SONGBIRD

A monogamous mating system that includes extrapair fertilization can potentially generate higher variability in male reproductive success than monogamy without extrapair fertilization. That increased variability could provide a correspondingly higher opportunity for sexual selection and, thus, for the origin and persistence of sexual dimorphism in monogamous species.

Bruce E. Byers et al, The Auk 121(3):788-795, 2004