Haemosporidian infections are more common in breeding shorebirds than in migrating shorebirds

Migrating animals are thought to be important spillover sources for novel pathogens. Haemosporidians (malaria-related parasites) are one such group of pathogens that commonly spillover into novel host communities if competent vectors are present. In birds, shorebirds (sandpipers, plovers and allies) perform some of the longest avian migrations, yet they are traditionally perceived as relatively free from haemosporidians. Although low prevalence fits several theories, such as effective immune responses or low exposure to vectors, few studies have been carried out in freshwater inland sites, where the vectors of haemosporidians (e.g. mosquitoes) are abundant, with a mixture of actively migrating (staging) and breeding hosts. Here we report the prevalence of three haemosporidian parasites, Haemoproteus, Leucocytozoon and Plasmodium, screened in 214 shorebirds from 15 species sampled in a freshwater marshland, southern Belarus. Contrary to most previous studies, we found that haemosporidians were frequent, with an overall prevalence in the community of 16.36%, including the locally breeding shorebirds (23.13%, 134 individuals of 10 species). However, actively migrating shorebirds had much lower prevalence (0.05%, 55 individuals of five species). We suggest that blood parasite infections are more common in shorebirds than currently acknowledged. Yet, actively migrating species may be free from haemosporidians or carry suppressed infections, leading to lower prevalence or even apparent absence in some species. Taken together, we theorize that a combination of sampling biases has driven our understanding of haemosporidian prevalence in shorebirds and future studies should take the migratory status of individuals into account when reporting prevalence. Furthermore, we argue that birds undergoing active migration may be less likely sources of spillover events than previously assumed.