Immunological defenses in large part determine the outcome of host-pathogen interactions, and as such are critical to the host for maintaining health and protecting future reproductive potential. The immune system is complex and responsible for many types of protective function, each of which differs in costs and benefits. Ecological characteristics and life history strategies are expected to shape the way that different hosts utilize their immune defenses, but large-scale comparative studies of the immune system across species are rare. We quantified two types of constitutive immunity, natural antibodies and complement, across 70 tropical bird species from 11 families. Despite extensive ecological and taxonomic variation and probable differences in pathogen exposure among species, we found consistent relationships between constitutive immune measures and species-level life history and ecological characteristics such as incubation period, clutch size, and social system. We will also present results on the relationships between metabolic response to an inflammatory stimulus, a functional measure of the capacity to kill bacteria, and life history parameters in a subset of tropical and temperate avian species. Ultimately, datasets such as this one will increase our understanding of the ecological and evolutionary forces that determine the nature of host-pathogen relationships.