MERCURY IN HERONS, EGRETS, AND THEIR FOODS

Mercury concentration levels were measured in herons and egrets and their food collected in the southwestern Lake Erie region. We analyzed primary wing feathers, breast muscle, liver, and brain tissues from 42 great blue herons (Ardea herodias), 44 black-crowned night herons (Nycticorax nycticorax), and 43 great egrets (Casmerodius albus). Concentrations were higher in island nesting birds than birds collected at the Winous Point Shooting Club, with primary wing feathers the highest, followed by liver, breast muscle, and brain tissues. Mercury levels in breast muscles, liver, and brain tissue of adult birds correlated (P < 0.01) within each population. Tissues of adult birds exhibited higher (P < 0.05) mercury concentrations than did tissues from nestlings of the same population. An importance index for each population of birds showing the significance of individual food items as sources of mercury indicated that birds nesting on West Sister Island acquired mercury from fish species found more frequently in Lake Erie than in marshes. Mercury concentration factors of the Lake Erie marsh ecosystem show a relationship between trophic levels and mercury concentration levels.