FACTORS CONTRIBUTING TO MALE MATING SUCCESS IN THE POLYGYNOUS DUSKY WARBLER (PHYLLOSCOPUS FUSCATUS)

In a mating system where females obtain multiple benefits from choosing a partner, male reproductive success will depend on a variety of factors. Females may seek (1) a high-quality territory (2) a good parent and (3) good genes for offspring viability. Looking at the dusky warbler Phylloscopus fuscatus, a system of resource-defence polygyny, I try to establish the relative importance of these factors for determining male mating success. Male success in social pairing (i.e. harem size) largely depended on territory quality and thereby on success in competition over the best territories. Old males and males with high body mass had a greater chance of mating polygynously, while first-year males and males of low body weight more often remained unmated. In addition, males with long tails were more likely to stay unmated. Interestingly, males with long tails contributed less to offspring care, which suggests that the social mating decisions of primary females also depended on the readiness of males to provision the young. Analysis of extra-pair paternity showed that females did not prefer to copulate with males that were most successful in competition over territories. Nevertheless, polygynous males, on average, sired 3.4 times more offspring than monogamous males. Socially unmated males sired 0.7 times as many. In general, variation in competitive ability had a roughly two times larger effect on male mating success than variation in male attractiveness. The effect of variation in parental qualities was probably less than one tenth of the effect of competitive ability.