RESUMO
The dynamics of the intestinal helminth fauna of wood ducks (Aix sponsa) and the relationship between changes in food habits and helminth populations during the bird's reproductive cycle were studied in southeast Missouri. A total of 11 species of helminths, comprised of four species of trematodes and seven species of cestodes, were recovered from the digestive tracts of 155 wood ducks. All species except one were found in both sexes. Significant differences were found in parasite numbers by season (spring vs. fall), sex, and stage of the reproductive cycle. Helminth infection in both sexes was higher in the spring than during fall courtship; however, the magnitude of the seasonal difference was considerably greater in females. Females contained significantly more helminths than males during spring, but no sex-related differences were detected in the fall. Seasonal changes and sex-related differences in parasite numbers corresponded closely with the consumption of invertebrates that serve as intermediate hosts. The average number of parasites in females was similar during fall courtship and pre-egg-laying, suggesting that little or no new infection occurred during winter. The most intensive infections were found in laying females and were attributed to hyperphagia and increased invertebrate consumption during egg production. A large decrease in the parasite numbers in females between incubation and fall courtship indicated that most of the helminths acquired by laying females were lost during summer; therefore, the long-term effects of the increased infection are probably negligible.