Relationships between nestling condition and variability in coccidian prevalence among three species of wild-nesting birds in New Zealand

Coccidian protozoa are widespread intestinal parasites of vertebrate species. Currently, our understanding of the dynamics of host-coccidia relationships among birds remains poor beyond domestic poultry and species held in captivity. The various threats that parasites can impose have resulted in demands to monitor and quantify different parasites and incorporate their impacts on hosts into ecological models of risk assessment. Here, we estimate prevalence of coccidian infections from nestlings of three species of exotic, free-living European passerines in New Zealand (Turdus merula, T. philomelos, Sturnus vulgaris). We find that despite high prevalence of infection among clutches (similar to 40%) these infections appear asymptomatic and are not related to indices of nestling condition or fledging success. We encourage additional studies to provide results on variation in parasite prevalence and pathogenicity in order to build our understanding of host dynamics.