Migration and parasitism: Habitat use, not migration distance, influences helminth species richness in Charadriiform birds

Aim: Habitat use and migration strategies of animals are often associated with spatial variation in parasite pressure, but how they relate to one another is not well understood. Here, we use a large dataset on helminth species richness of Charadriiform birds to test whether higher habitat diversity and seasonal migration increase parasite richness in avian hosts. Location: Global. Methods: We compiled a global dataset on helminth species richness, habitat use strategies (marine/freshwater/mixed wintering and osmotic generalist/specialist) and various ecological/life-history traits (migration distance, geographical range size, diet, body mass, sampling latitude) of Charadriiform birds. To test if hosts with different habitat use strategies encounter different parasite pressures, we used comparative methods that correct for shared ancestry and phylogenetic uncertainty. Results: Habitat generalists (mixed wintering habitats and osmotic generalists) harboured more parasite species than habitat specialists; marine- and freshwater-restricted hosts had similar helminth species richness. Contrary to previous results, we found no association between parasite species richness and migration distance. Overall helminth species richness also increased with diet diversity, with no effects of other ecological/life-history traits. Main conclusions: We suggest that birds exploiting diverse habitats and diets are exposed to a more diverse parasite fauna and conclude that distribution patterns and habitat use, rather than migration distance, shape parasite diversity within host populations. Overall, these results demonstrate the significant role of habitat use in explaining how migration may indirectly affect parasite richness in host populations.