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 species (ducks, geese and swans) in relation to host migration patterns. Whilst controlling for research effort, the number of parasite species or genera reported per host was positively related to migration distance, but not to breeding latitude or size of the breeding or total annual range. In species undergoing longer distance migrations, a higher proportion of individuals were infected by haematozoa. Thus, there is indeed evidence that migratory birds are more susceptible or are exposed to a more diverse parasite fauna and higher risk of infection. This may help to explain why migratory species tend to have more exaggerated, sexually selected traits as well as larger immune system organs.