Prevalence of Hematozoa in Overwintering American Redstarts (Setophaga ruticilla): No Evidence for Local Transmission

We examined American redstarts (Setophaga ruticilla) for protozoan blood parasites on their wintering grounds to determine whether transmission of these parasites occurs prior to spring migration. A total of 73 blood smears from 37 birds were examined for presence and intensity of infection. Thirty-six birds were sampled in the fall, soon after arriving from northern breeding grounds, and the spring prior to departure. Two (5%) of the samples collected in the fall were positive for Haemoproteus fringillae and one (3%) had detectable infections of Trypanosoma avium. Individuals infected with H. fringillae were hatching year redstarts sampled in September and October. Intensity of infection was 78 and <1 infected erythrocytes per 10,000 erythrocytes, respectively. None of the birds had detectable infections when resampled prior to spring migration the following March.