The digestive tracts of 771 lesser snow geese (Chen caerulescens) collected from January to May 1983 from 12 locations (27 Samples) were examined fro helminth parasites to determine whether parasite species present in wintering geese or in spring migrants occurred independently of each other. Nine helminth species were identified. Seven had mean prevalances >5% and were the focus of this study. Six of those species were waterfowl generalists, one was a goose specialist. Our primary objective was to assess the potential contribution of factors, other than species interactions, in determining paterns of co-occurance between helminth species. There were few negative relationships between helminth species, regardless of whether presence-absence or abundance data were used. However, some species pairs showed recurrent and significant co-occurances. There were similar and significant effects of timing of sampling, host gender, and host age, on prevalance and mean abundance of particular species. Co-occurances were found for those species that showed seasonal declines in prevalence, for those expected to have colonizing abiliaty based on host age profiles (using abundance data), and for abundant species that may have shared vectors or environmental conditions favorable for transmission. Thus, similarities between parasites in their abundance,transmission biology, and phenology seem sufficient to expain species co-occurances without invoking other processes such as species interactions.
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