Blood parasite prevalence in the Bluethroat is associated with subspecies and breeding habitat

Long-distance migratory birds are potentially exposed to a range of blood sucking arthropods that transmit avian blood parasites. Because of differential vector exposure, the parasite fauna may vary in different habitat types, among populations, or even within populations where individuals travel to different areas during migration. We applied PCR-based molecular techniques to determine patterns of blood parasite occurrence in adults of seven geographically isolated Bluethroat populations, belonging to three distinct subspecies differing in habitat preferences and wintering areas (Luscinia svecica svecica, L. s. cyanecula, L. s. namnetum). Moreover, to elucidate potential transmission of blood parasites on breeding sites, we tested adults of the relatively sedentary White-throated Dipper (Cinclus cinclus) from a Norwegian population. Across populations, we detected infection of at least one blood parasite genus in 68.5 % (139/203) of adult Blue-throats. The most common parasite genus was Plasmodium (10 lineages, 33.5 % of surveyed individuals), present in all seven populations, followed by Leucocytozoon (four lineages, 31.5 %) and Haemoproteus (two lineages, 4.9 %). We recorded multiple infections in 26.1 % of individuals. Leucocytozoon was found only in svecica inhabiting mountainous/subalpine areas with high abundance of blackflies, the main vector for this parasite. In Plasmodium, two lineages (BT6 and GRW4) were confined to specimens from svecica populations. In contrast, Lineage SGS1 was dominated by southern birds of the subspecies cyanecula and namnetum. Our data suggest transmission of Leucocytozoon on the breeding grounds in Norway as the same lineages were found in relatively sedentary White-throated Dippers as in migratory Bluethroats. We discuss these results in light of the ecological differences between the host populations, affecting their exposure to potential blood parasite vectors.