Transmission of gastrointestinal bacteria, Campylobacter spp. and Salmonella spp., from wild birds may have serious consequences for human health and poultry industry. Despite this, our knowledge on the distribution of these bacteria in wild avian populations is limited. Since both genera markedly differ in their pathogenicity in wild birds (Campylobacter is largely non-pathogenic, while Salmonella is a major pathogen), I expected that their occurrence and modes of transmission can be associated with different ecological and life-history traits of their avian hosts. To test this hypothesis, I retrieved nearly 700 estimates of Campylobacter and Salmonella prevalences in 200 avian species and implemented phylogenetically-informed comparative analysis to examine variation in their prevalence. Campylobacter had wider phylogenetic distribution and higher average prevalence in birds than Salmonella. Campylobacter prevalence showed strong associations with basic life-history components of birds (body mass, development rate, and longevity), while Salmonella prevalence was primarily determined by ecological traits (sociality and urbanization). The results also provided support for biogeographical differences and contrasting temporal trends in the occurrence of these bacteria in birds. The study helps to explain the patterns of Campylobacter and Salmonella distribution in wild bird populations from a broad phylogenetic perspective and it might be helpful to establish successful policies aiming to reduce a negative impact of these bacteria on both human health and poultry industry.