Organochlorine Residues in Three Species as Related to Diet and Age

Levels of organochlorine residues were determined in whole body and tissue samples of three heron species collected in northeastern Louisiana. Residue levels were assessed in relation to differences in diets and ages. Every bird analysed contained at least one organochlorine contaminant; DDT and its metabolites and PCBs were the principal residues detected. DDE, DDT, and other residues were higher in green-backed than in little blue herons, which in turn contained higher chemical levels than those of yellow-crowned night herons. These concentrations reflect contamination levels of their foods. Mean concentrations tended to be lower in immature herons than adults of the same species. ( 13 references, 4 tables, )