Hg concentration levels were measured in herons and egrets and their foods collected in the southwestern Lake Erie region. 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) were analyzed. 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. Hg levels in breast muscle, liver and brain tissue of adult birds correlated (P < 0.01) within each population. Tissues of adult birds exhibited higher (P < 0.05) Hg 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 Hg indicated that birds nesting on West Sister Island acquired Hg from fish spp. found more frequently in Lake Erie than in marshes. Hg concentration factors of the Lake Erie marsh ecosystem show a relationship between trophic levels and Hg concentration levels.