Effects of salinity on rates of infestation of waterbirds by haematozoa

A recent hypothesis suggested that migration patterns in waders and other birds could be shaped by the distribution of parasites and diseases. This hypothesis assumes a reduced exposure to parasites in species living in saline habitats. To test this assumption, the number of species of haematozoa and rates of infection reported for bird species living in fresh and salt-water habitats were compared. Species living in more saline habitats had fewer haematozoic parasite species than freshwater birds. Relative frequency of infection was also lower in saltwater species. Neither phylogeny nor the number df individuals examined for blood parasites in each species explained these differences. Thus, there is indeed evidence that birds living in saline habitats have a reduced risk of being parasitized by haematozoa, probably due to a reduced abundance of the invertebrate vectors.