Extra-pair fertilizations increase the opportunity for sexual selection in the monogamous House Martin Delichon urbica

While many studies have reported extra-pair paternity in birds, few studies have actually been able to assign paternity to extra-pair young or to determine correlates of male extra-pair fertilization success. Such information is crucial when trying to evaluate the factors that influence male reproductive success and female mate choice. In this two year study we used DNA fingerprinting to assign paternity to all young in a small colony (9-11 nests) of socially monogamous and monomorphic House Martins Delichon urbica. Overall, extra-pair paternity accounted for 19% of young and occurred in 35% of broods. All extra-pair young were sired by just four males in the colony,. in some cases these males lost paternity to each other. The variance in total fertilization success was larger than the variance in apparent success (i.e. brood size) indicating that extra-pair fertilizations increased the opportunity for sexual selection. Males with higher total fertilization success (within-pair and extra-pair) were heavier and survived better to the next breeding season than males with lower total fertilization success. These results indicate that male quality is correlated with fertilization success, although we do not know if this is due to female choice, male-male competition, or both.