Haematozoan parasites and migratory behaviour in waterfowl

Although it has been suggested that migratory species are exposed to a more diverse parasite community than sedentary species, this has not previously been demonstrated. To test this hypothesis, we analysed the diversity and prevalence of infections by haematozoan parasites reported in anseriform sp ecies (ducks, geese and swans) in relation to host migration patterns. Whil st controlling for research effort, the number of parasite species or gener a reported per host was positively related to migration distance, but not t o breeding latitude or size of the breeding or total annual range. In speci es undergoing longer distance migrations, a higher proportion of individual s were infected by haematozoa. Thus, there is indeed evidence that migrator y birds are more susceptible or are exposed to a more diverse parasite faun a and higher risk of infection. This may help to explain why migratory spec ies tend to have more exaggerated, sexually selected traits as well as larg er immune system organs.