Changes in egg composition of American kestrels exposed to dietary polychlorinated biphenyls

Changes in the quality of eggs of birds exposed to polychlorinated biphenyl s (PCBs) have been described, but have never been directly attributed to PC Bs. Polychlorinated biphenyl residues in eggs have been associated with red uced reproductive success and embryonic deformities in wild birds. Egg size and composition, specifically the amount of albumen, yolk, and water in an egg, also influence the growth and viability of embryos and hatchlings, an d consequently the reproductive success of birds. To determine whether PCB exposure of adult birds affected the size and composition of their eggs, 25 pain of captive American kestrels (Falco sparverius) were fed a mixture of PCB-spiked (1248:1254:1260) food to give an approximate exposure of 7 mg/k g body weight/d, beginning 1 mo prior to pairing, and continuing throughout the courtship, egg-laying, and incubation periods. This dietary level in t he adult female kestrels resulted in mean total PCB residues in the eggs of 34.1 mu g/g wet weight (geometric mean), which is environmentally relevant . PCB residues in eggs increased with the time of female exposure to the co ntaminated diet and laying dare. Variation in Egg size within PCB clutches was significantly greater than within control clutches, although absolute e gg mass and volume did not differ markedly by treatment. Only infertile egg s and only one egg per clutch were used for egg composition analysis. Yolks in the PCB-contaminated eggs were heavier, with less wet and dry albumen r elative to control eggs. Water content and eggshell thickness were not sign ificantly affected by PCB exposure. These results suggest that eggs from th e PCB treatment have relatively more lipid and less protein available for e mbryonic development. Changes in egg composition were not associated with e gg size, lay date, ambient temperature, humidity, or precipitation, which a re factors known to affect these variables in bird eggs. The PCB-induced ch anges in egg composition described here provide insight into possible mecha nisms contributing to reduced reproductive performance in wild birds expose d to PCBs.