From sea to summit: shifting patterns of avian haemosporidian diversity across two Malagasy study sites

Abstract Island ecosystems such as those in Madagascar host a highly endemic biodiversity which is strongly shaped by geology, habitat structure, altitude, and anthropogenic impact. These factors could further shape the prevalence and diversity of avian haemosporidian parasites ( Haemoproteus , Plasmodium and Leucocytozoon ). To assess how contrasting habitats affect shifting patterns in parasite prevalence and lineage richness, we examined samples from three widespread Malagasy bird species: Cinnyris sovimanga (Nectariniidae), Hypsipetes madagascariensis (Pycnonotidae), and Terpsiphone mutata (Monarchidae) across two ecologically distinct environments: the mid-altitude rainforest of Maromizaha (800–1200 m) and the oceanic island of Nosy Saba (at sea level). Of the 167 blood samples analysed, 50.9% were positive for haemosporidian parasites using molecular methods, whereas 56.3% of 119 blood smears were positive using morphological methods. In total, twenty-five distinct haemosporidian lineages were identified. The Maromizaha rainforest harboured a higher lineage diversity and prevalence of Haemoproteus and Leucocytozoon , consistent with its structurally complex habitat composition. In contrast, Nosy Saba Island harboured higher Plasmodium prevalence (95.4%), likely reflecting a greater abundance of mosquito vectors in a structurally simple habitat. Yet, Plasmodium lineage diversity was higher in Maromizaha, suggesting that vector abundance does not necessarily translate into vector diversity. These findings show a likely influence of habitat structure and vector ecology in shaping haemosporidian parasite infections. While humid, continuous forests support greater parasite diversity, degraded island habitats may favor dominance by generalist lineages. Future studies combining vector sampling with host–parasite data will be essential for understanding transmission dynamics across contrasting habitats, especially across Madagascar’s heterogeneous landscapes.