Embryonic development period and the prevalence of avian blood parasites.

Variation in prevalence of avian hematozoa is related to taxonomic affiliation at the level of the family or subfamily but not of the genus within families. Prevalence is comparatively insensitive to the influences of habitat and season; however, temperate species have higher incidences of infection than tropical species belonging to the same families. Among taxa of nonraptorial altricial landbirds, hematozoan prevalence is inversely related to the length of the incubation period but shows little relationship to body size and rate of postnatal development. This finding suggests a possible link between the duration of embryonic development and the ability to resist or control infection, possibly due to maturational processes in the avian immune system.