Spatial and temporal differences in the blood parasite fauna of passerine birds during the spring migration in Bulgaria.

Species composition and prevalence of the blood parasites of three migratory Acrocephalus species of warblers (Acrocephalus arundinaceus, Acrocephalus scirpaceus and Acrocephalus schoenobaenus) were studied during spring period in Bulgaria. For each of the studied species, we compared the parasite fauna during their spring migration at three study sites in search of infection patterns in time and space. Spatial differences were registered in the blood parasites and their prevalence for two of the studied species-A. arundinaceus and A. scirpaceus, whereas for the third one-A. schoenobaenus, there were no significant differences. The parasite species Haemoproteus belopolskyi was present in migrating A. arundinaceus only at Kalimok station, but not at the other two sampling locations. Plasmodium prevalence in A. arundinaceus migrating through Kalimok was also different between years. A decrease of H. belopolskyi prevalence was detected for A. schoenobaenus at Petarch during the spring of 2006. On the contrary, Plasmodium (Haemamoeba) sp. infections of the same bird species increased during the spring period. The differences found between sites could be explained with the different origin of the migrants at different migration stopover points. Climatic conditions and vector abundance in the zones of origin are probable reasons for the observed differences between years.