Metazoan Parasites

Abstract

A plethora of metazoa have been described from wild waterfowl (Lapage, 1961; McDonald, 1969a,b, 1974a,b, 1981, 1988; McLaughlin, 1990). The significance and actual effects of most of these are unclear; however, “the host must pay a ‘price’ for harbouring parasites that live, grow, and reproduce at the expense of the host” (Yuill, 1987). Discussion here is limited to parasites that have been reported to be pathogenic. Most parasites are of greatest significance in young naive hosts, and this is the group among which one would expect the greatest occurrence of parasitic disease. Waterfowl breed in inaccessible regions or spread diffusely over very large areas, so there has been little research on the diseases of newly hatched or premigratory birds. Most studies of disease and parasitism have dealt with populations in which all birds were at least several months of age. Conclusions reached about the significance of parasites in such studies may be misleading. The Common Eider is one of the few species in which posthatching disease has been studied intensively; parasitic disease due to protozoa and metazoa appears to be common and important in that species. Unfortunately, comparable data are lacking for other waterfowl.