Use of a homing pigeon (Columba livia) model to assess the effects of cholinesterase inhibiting pesticides on non-target avian species

Cholinesterase inhibiting compounds such as carbamates and organophosphate insecticides have been widely used in agriculture since the ban on organochlorines in the 1970s. Although these compounds are very effective against target insects and other pests, incidental morbidity and mortality on non-target species has also been well documented. Among the most vulnerable non-target species are birds. Despite efforts to minimize non-target exposure to these pesticides, birds continue to be exposed. These studies were designed to investigate the impact of sub-lethal exposures to carbamate or organophosphate pesticides on avian species. In the studies, homing pigeons (Columba livia) were used as surrogate species to assess the differences in the effect of low-level and environmentally relevant doses of aldicarb, a carbamate, and chlorpyrifos, an organophosphate, two of the most widely used pesticides in California and the nation as a whole. Time of flight analyses were performed and results indicated a significant increase in flight times after aldicarb exposure at 0-0.5 mg/kg and a slight effect from chlorpyrifos at 0-5 mg/kg. In a second experiment, the pigeons were utilized for trials on reproductive effects looking at fertility measurements, egg shell thickness, and post-hatch weight measurements. After exposure to either compound egg numbers were minimally affected, but aldicarb dosed birds resulted in fewer healthy offspring and smaller chicks. Exposure to chlorpyrifos increased egg shell thickness, and exposure to aldicarb decreased it. A final study was designed to compare the effects of the compounds on plasma cholinesterase activity over a time course. The results indicated a dose-dependent decrease in activity associated with chlorpyrifos exposure at 0-7.5 mg/kg and a decrease to 10 percent of normal activity after aldicarb exposure at 0-1.0 mg/kg. These studies suggest that low-dose exposure to these chemicals can have population level effects in these birds, and the results validate the homing pigeon as a good subject for comparative studies of cholinesterase inhibitors in birds and the need for further research on repeated low-level exposures on populations of avian species.