An analysis of gizzard worm infections in fall migrant ducks at Delta, Manitoba, Canada
Gizzards from 13 species of ducks collected during the 1979 hunting season at Delta, Manitoba, Canada, were examined for helminths. Of the 1196 gizzards examined, 77.7% harbored at least one species of helminth. Amidostomum acutum occurred in 53.3% of the gizzards (13 species); Epomidiostomum uncinatum, in 28.5% (10 species); Streptocara crassicauda, in 18.1% (12 species); Gastrotaenia cygni, in 17.8% (11 species); and Streptocara formosensis, in 3.7% (5 species). Infection levels in juveniles and adults and in males and females of the same age in each species were generally similar. Prevalence and abundance of A. acutum in dabbling ducks (Anas spp.) was greatest among species exhibiting intermediate or generalist foraging tactics. Redheads and canvasbacks had the heaviest infections among diving species. The intermediate and generalist Anas species also had the greatest prevalence and abundance of E. uncinatum. With the exception of ruddy ducks, divers were rarely infected with this helminth. Lesser scaup were the major hosts for the Streptocara species and prevalence in other hosts tended to reflect the importance of amphipods in the diet. Shovelers, which feed extensively on zooplankton, had the highest prevalence of G. cygni. Few significant differences were found in the mean intensity of each helminth among host species despite wide differences in prevalence. Thus while diet and (or) foraging strategy may affect a species' contact with the infective pool, it apparently has little effect on the size of the infection which results.