Annual egg productivity predicts female-biased mortality in avian species

Among avian species, the differential cost entailed by either sex in competition for mates have been regarded as the main evolutionary influence on sex differences in mortality rates. However, empirical evidence suggests that sex-biased adult mortality is mainly related to differential energy investment in gamete production, a greater annual mass devoted to egg production leading to higher female mortality. We explicitly tested the generality of this pattern in a comparative framework. Annual egg production can be relatively large in some species (up to 200% of female body mass) and annual mortality is generally biased towards females. We showed that greater annual egg productivity resulted in higher mortality rates of females relative to males. Mating system was secondarily important, species where males were more involved in mating competition having more equal mortality rates between the sexes. However, both traits explained only a limited fraction of the interspecific variation in f...