MERCURY IN LIVERS OF WADING BIRDS (CICONIIFORMES) IN SOUTHERN FLORIDA

Mercury was measured in livers from 144 wading birds representing seve n species collected from four different areas in southern Flordia, inc luding the Everglades National Park. Significant differences in hepati c mercury concentrations were identified between birds collected from different geographic locations, birds of different ages, dietary facto rs, and relative amounts of body fat. Birds collected from an area enc ompassing the central Everglades and eastern Florida Bay had significa ntly greater concentrations of hepatic mercury than did birds from oth er collection areas. Livers from fledgling and young adult birds conta ined approximately three times the concentration of mercury as livers from nestling birds. Bird species whose prey base consists of larger f ish were found to have approximately four times the hepatic concentrat ion of mercury as did those species which consume smaller fish or crus taceans. Birds with minimal to moderate amounts of body fat had two to three times the concentration of hepatic mercury as birds with relati vely abundant body fat reserves. Four great blue herons collected from the central Everglades contained liver mercury at concentrations typi cally associated with overt neurologic signs (greater than or equal to 30 mu g/g). Between 30% and 80% of potential breeding-age birds colle cted from this area contained hepatic mercury at concentrations associ ated with reproductive impairment in ducks and pheasants. These data s uggest that declining numbers of nesting ciconiiform birds in Florida may be due, in part, to mercury contamination of their food supply.