Male Biased Parasitism in Cormorants and Relationships with Foraging Ecology on Lake Erie, Canada

Existing hypotheses only partially explain male biased parasitism in mammals and birds. The present study examined whether male biased parasitism by a common trematode and nematode exists in breeding Double-crested Cormorants (Phalacrocorax auritus) from Lake Erie and if any sex bias in parasitism could be explained by sex differences in body size and foraging ecology, evaluated using stable isotope profiles (based on delta C-13, delta N-15). Male cormorants had three times the abundance of Drepanocephalus spathans (a trematode) than females; however, there were no significant sex differences in abundance or intensity of Contracaecum spp. Relationships between body size and parasitism were either non-existent or inconsistent. Stable carbon isotope profiles indicated that male and female cormorants that foraged in more pelagic habitats had more Contracaecum spp. In summary, male biased parasitism was present in a sample of Lake Erie cormorants and differences in foraging ecology might affect the levels of parasitism in cormorants. Received 8 October 2009, accepted 24 March 2010.