Host-Parasite Catalogue of the Helminths of Ducks

Abstract

That ducks, both wild and domestic, are of considerable economic importance is not to be questioned. Millions of dollars are spent each year by hunters, and the economic value of domestic ducks is considerable. For a number of years the numbers of wild ducks have steadily declined, and during the drought years, the population reached such a low level that a general alarm was sounded. Since that time, much activity has been pointed at learning the causes and remedies for the situation. While the problem of diseases and parasites has been considered, it has been worked on very little, especially at the breedintg grounds among young ducks, and consequently, our knowledge of its importance is very limited. Ducks, being for the most part aquatic feeders, are particularly subject to helminthic infection. In areas where large numbers congregate to nest and raise young, this factor is considerable in importance. What effect such helminthic infections may have on the total duck population is unknown. The probable degree of infection is more or less in direct proportion to the crowding during the nesting and rearing period, and in drought years when other factors are most adverse to rearing young, this factor also would reach its peak of importance. The host-parasite relationship of ducks and their helminth parasites is influenced by many factors. Ducks, both as individuals and as a group, show remarkable ability to harbor parasites with little or no inconvenience to themselves. Relatively few of the ducks that have been examined by the writer have been entirely free of helminths. Too, some 260 species of worms have been recorded in the literature from this group of birds, and is an extensive fauna to say the least. A careful examination of the following host-lists will indicate that, for the majority of helminths, there is little, if any physiological host specificity among species of ducks. Such parasitic limitation as is evident can, in most cases, be explained on the basis of physical reasons, such as inaccessibility of infective larvae to certain species by reason of feeding habits. It is self evident that of such a large group of helminth parasites, relatively few of the species are of any considerable degree of importance as pathogenes. The most important consideration from this standpoint is the patential pathogenicity of any parasite, and the probable greater degree of damage in the young host. The habits of the hosts play a very important role in the relationships. The annual migration serves to disseminate the parasites, and of especial importance is the cross migration and wandering of the birds following the breeding season and preceeding the beginning of the fall migration. This allows for widespread dissemination of the parasites over the breeding grounds. Of some importance, is the proven fact that ducks may act as reservoir hosts 580