Sex-specific parasite prevalence is predicted by sexual size dimorphism in wild birds

Males and females often differ in ecology and behaviour, and these differences are expected to lead to sex differences in parasite susceptibility. However, sex differences in parasite prevalence have not yet been established across a broad range of taxa, and the ecological and evolutionary drivers of such differences have remained contested. Here we meta-analyse 942 sex-specific effect sizes in blood and gastrointestinal parasites of 179 wild bird species, representing 17 avian orders. Females exhibit higher infections in both Haemoproteus and Protozoan parasites than males and females also have higher prevalence in both Leucocytozoon and Haemoproteus blood parasites during the breeding season. Importantly, sex differences in parasite prevalence are not associated with sexual selection nor parental care, although male-biased prevalence in Leucocytozoon parasites were predicted by male-biased size dimorphism. Taken together, breeding systems and sexual selection have modest influence on sex difference in parasite prevalence across the avian tree of life.