Effects of dietary PCB exposure on adrenocortical function in captive American kestrels (Falco sparverius)

We experimentally examined the effects of dietary exposure to polychlorinated biphenyls (PCBs) on adrenocortical function in American kestrels (Falco sparverius). Nine captive male American kestrels previously exposed to a PCB mixture (Aroclor 1248:1254:1260; 1:1:1) in their diet were subjected to a standardized capture, handling and restraint protocol designed to produce an increase in circulating corticosterone. A similar protocol has been applied to a wide range of avian species and was used here to evaluate the response of PCB-exposed and control kestrels to a defined physical stressor. Both baseline and stress-induced corticosterone levels were significantly lower in PCB-exposed birds when compared with control birds of the same age. PCB-exposed birds exhibited significantly lower corticosterone levels during the corticosterone response when compared with control birds, independent of body condition. Furthermore, baseline corticosterone concentrations exhibited a hormetic response characterized by an inverted U-shaped dose response in relation to total PCB liver burden. These results support several recent studies which report decreased levels of circulating corticosterone in PCB-exposed wild birds. The results presented here provide the first evidence that exposure to an environmentally relevant level of PCBs (approximately 10 mg/kg body weight) can impair the corticosterone stress response in kestrels, potentially increasing the susceptibility of birds to environmental stressors such as severe weather and predatory and human disturbance.