Characterization of haemosporidian infections in warblers and sparrows at south-western European reed beds

The prevalence and intensity of avian haemosporian infections (genera Haemoproteus and Plasmodium) were investigated using molecular techniques and microscopy in nine passerine species at three Portuguese reed beds along a small latitudinal gradient. The effect of age, sex, season, site and year in the infection prevalence was evaluated for some of these host species. Of the sampled birds, 34.5% were infected, all with low level parasitemias. Haemoproteus spp. was only present in migrant species and was not locally transmitted, while Plasmodium spp. infected more species and reached a higher overall prevalence. Prevalence differed among bird species and was affected by different variables for each species: it was associated with age in the Reed Warbler Acrocephalus scirpaceus, with season in the Cetti’s Warbler Cettia cetti and with year in the House Sparrow Passer domesticus. Site did not influence prevalence for any species at this small geographical scale. Reed Warbler adults had already migrated to Africa and contacted with two different parasite faunas, whereas juveniles had not, thereby explaining the importance of age to explain parasitemia in this species. For the resident Cetti’s Warbler, prevalence varied significantly with season, perhaps due to lower food availability in autumn and winter, making birds weaker and more prone to infection.