Abstract
A survey of 3319 wild ducks shot on the Delta Marsh, Manitoba, in 1977 and 1978 revealed that 10.0% of Anas spp. harboured Typhlocoelum cucumerinum cymbium and 9.9% of Aythya spp. harboured Typhlocoelum cucumerinum cucumerinum. The American wigeon, Anas americana Gmelin, and the ring-necked duck, Aythya collaris (Donovan), are recorded as new hosts for T. cucumerinum. Data were analysed for differences in prevalence, abundance, and intensity of infection among host species, and for seasonal, age, and sex differences within host species. Prevalence ranged from 0.0% in gadwall to 31.4% in canvasbacks; mean intensity ranged from 1.0 in wigeon to 3.8 in canvasbacks. Theoretical frequency distributions for abundance of T. cucumerinum were constructed and compared with the data for each host species. Eight of 10 had a negative binomial distribution and 2 had a Poisson distribution. Two potential explanations for the variation in distribution of T. cucumerinum among host species were investigated: susceptibility and feeding ecology. Firstly, it was shown experimentally that gadwall, mallard, blue-winged teal, and canvasback ducklings are equally susceptible to the initial stages of infection. Secondly, there was a positive correlation between T. cucumerinum infections and occurrence of snails in the diet of the various host species.
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