Mercury contamination in free-ranging great egret nestlings (Ardea albus) from Southern Florida, USA


Between March and June of 1994 and 1995, mercury (Hg) concentrations were determined from 393 blood and 164 growing scapular feathers from 252 great egret nestlings (Ardea albus). Nestlings came from eight colonies located in Water Conservation Area 3 in the Everglades region in southern Florida. The ages of these birds ranged from 1 to 44 d (bill length 1.1 to 10.2 cm). Mercury concentrations in blood and feathers of first-hatched great egret nestlings sampled during 1994 averaged 1.2 μg/g (range = 0.07–3.9) wet weight and 16 μg/g (4.5–40) dry weight, respectively. During 1995, first-hatched chicks had blood and feather Hg concentrations that averaged 0.8 μg/g (0.2–1.7) and 9.7 μg/g (2.3–26), respectively. In both years, Hg concentrations in blood and feathers were significantly correlated, and a significant correlation also was found between Hg in blood and age of the chicks. Blood and feather Hg concentrations differed significantly between years, with higher concentrations during 1994. Birds from JW1 and L67 colonies had the highest concentrations of Hg in blood and feathers. Mercury concentrations did not differ between chicks of different hatch order. Mercury in feathers of great egret nestlings from southern Florida are approximately six times higher when compared to feather Hg concentrations of nestling wading birds sampled elsewhere.

Environmental Toxicology and Chemistry