Association of helminth infections and food consumption in common eiders Somateria mollissima in Iceland

Abstract

Common eider Somateria mollissima L. 1758, subsp. borealis, is widely distributed along the coasts of Iceland. In this study association of parasite infections and food composition was studied among 40 females and 38 males (66 adults, 12 subadults), shot under license on four occasions within the same year (February; before egg-laying in May; after the breeding period in late June; and in November) in Skerjafjörður, SW Iceland. Parasitological examinations revealed 31 helminth species (11 digeneans, ten cestodes, seven nematodes, and three acanthocephalans). Distinct digenean species parasitized the gallbladder, kidney and bursa of Fabricius, whereas other helminths parasitized the gastrointestinal tract. Thirty-six invertebrate prey species were identified as food; waste and bread fed by humans, were also consumed by some birds. Amidostomum acutum was the only parasite found with a direct life cycle, whereas other species were food transmitted and ingested with different invertebrate prey. Opposite to females male birds rarely utilized periwinkles and gammarids as a food source. As a result, Microphallus and Microsomacanthus infection intensities were low except in February, when subadult males were responsible for an infection peak. Females caring for young increased their consumption of periwinkles close to the littoral zone in June; during pre-breeding, females also increased their gammarid intake. As a consequence, Microphallus and Microsomacanthus infection intensities temporarily peaked. Increased food intake (including Mytilus edulis) of females before the egg-laying period resulted in twofold higher Gymnophallus bursicola infection intensity than observed for males. Profilicollis botulus infection reflected seasonal changes in decapod consumption in both genders. Different life history strategies of males and females, especially before and during the breeding season and caring of young, and during molting in distinct feeding areas in summer, promote differences in consumption of prey-transmitted parasites that result in distinct infection patterns of the genders.