Incomplete Female Knowledge of Male Quality May Explain Variation in Extra-Pair Paternity in Birds

Abstract

Abstract We present and discuss an hypothesis to explain inter- and intraspecific variation in levels of extra-pair paternity (EPP) in birds. In species with biparental care, females may be willing to engage in extra-pair copulation (EPC) to improve the genetic quality of the offspring. However, it may be costly to sample males and difficult to assess their genetic quality. Hence, we suggest that variation occurs in the extent of such knowledge between females, causing variation in the extent to which they are willing to engage in EPC. From the hypothesis we present nine predictions on occurrence of EPP in birds, e.g. cuckolders should mainly be resident, close neighbours; rate of EPP should be positively related to breeding density, to rate of male intrusion, to female opportunity to assess male quality from competitive interactions between males, to early arrival time of females relative to time of egg laying, and to breeding synchrony. Finally, we discuss implications on male behaviour. We suggest a new function of male mate guarding, namely that mate guarding is a means to prevent the social mate from obtaining essential information about the quality of potential extra-pair mates.