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 d etermined from 393 blood and 164 growing scapular feathers from 252 great e gret nestlings (Ardea albus). Nestlings came from eight colonies located in Water Conservation Area 3 in the Everglades region in southern Florida. Th e ages of these birds ranged from I to 44 d (bill length 1.1 to 10.2 cm). M ercury concentrations in blood and feathers of first-hatched great egret ne stlings sampled during 1994 averaged 1.2 mu g/g (range = 0.07-3.9) wet weig ht and 16 mu g/g (4.5-40) dry weight, respectively. During 1995, first-hatc hed chicks had blood and feather HE concentrations that averaged 0.8 mu g/g (0.2-1.7) and 9.7 mu g/g (2.3-26), respectively. In both years, Hg concent rations in blood and feathers were significantly correlated, and a signific ant correlation also was found between Hg in blood and age of the chicks. B lood and feather Hg concentrations differed significantly between years, wi th higher concentrations during 1994. Birds from JW1 and L67 colonies had t he highest concentrations of Hg in blood and feathers. Mercury concentratio ns did not differ between chicks of different hatch order. Mercury in feath ers of great egret nestlings from southern Florida are approximately six ti mes higher when compared to feather Hg concentrations of nestling wading bi rds sampled elsewhere.