Migratory birds spread their haemosporidian parasites along the world's major migratory flyways

Parasites circulate on a large scale through migrating hosts that encounter a wide diversity of parasites along their travels. This interaction can lead to greater similarity of parasite communities between regions connected by major migration routes. Additionally, migratory species may have higher importance (network centrality) within host–parasite networks. In this study, we test these two assumptions using globally recorded data on interactions between birds and avian malaria parasites (i.e. Plasmodium and Haemoproteus ). We first determined the similarity of haemosporidian parasite community between each biogeographic realm and the network centrality of each bird species within both the Americas and African–Eurasian flyways. Network centrality was measured by both the number of direct links involving a given species (degree centrality) and the extent to which that species indirectly links other species (betweenness centrality). Despite a high overall dissimilarity in haemosporidian parasite community compositions between biogeographic realms, we found lower values between areas connected by a known migratory flyway compared to non‐connected areas. Our results indicate that migratory species, when compared to sedentary ones, are more central both because they are connected to more parasites and connect other species in the interaction network of both the Americas and African–Eurasian flyways. Long‐distant migrants may directly affect the communities they visit by introducing high number of haemosporidian parasites, while at the same time they may become infected with the parasites present in these communities. Migrants therefore facilitate the spread of pathogens to some extent, and their presence can directly influence the dynamics and structure of local host–parasite networks.