Eggshell modifications in captive American kestrels resulting from Aroclor 1248 in the diet

American kestrels (Falco sparverius) were fed diets containing 3 μg/g Aroclor^® 1 1248 or control diets from mid-January until July. Eggs were removed from first clutches 2 to 4 days after laying ceased and shell thickness and shell dimensions were measured. Contents of the third egg of each clutch, the carcasses of all adults that received Aroclor^® 1248 and of three males and three females that received the control diet were analyzed for DDE, Aroclors^® 1248, 1254 and 1260, and dieldrin. Concentrations of PCBs, DDE and dieldrin were significantly higher (P < 0.03) in eggs and carcasses from treated adults than in controls. Shell thickness and shell thickness index of eggs from treated adults were reduced 5.0% (P < 0.0001) and 4.8% (P < 0.0001), respectively, from those of controls.