INTERACTIVE MORTALITY FACTORS IN COMMON LOONS FROM MARITIME CANADA

Between August 1992 and November 1995, 31 moribund or dead common loon s (Gavia immer) found in the three Maritime provinces of Canada (New B runswick, Nova Scotia, Prince Edward Island) were necropsied. Eight of these birds were in good body condition and died acutely from drownin g or trauma. The remaining 23 birds were in poor body condition and ha d either chronic lead poisoning, respiratory mycosis, or oil contamina tion of their plumage. Loons in poor body condition had significantly higher numbers of intestinal trematodes and significantly higher level s of total renal mercury than loons in good body condition. Therefore, poor body condition in many loons was associated with two or more con current potential disease processes, although we could not establish a cause-effect relationship among these processes in individual birds. These results suggest that mortality in chronically ill wild animals c an result from synergism among several potentially debilitating agents present in their environment.