Incidence of lethal bird poisoning reduced by regurgitation of pesticide-treated food

Regurgitation by birds feeding on pesticide-treated seed was quantified in two experiments, and its role in reducing the risk of acute poisoning from an organophosphorus pesticide was assessed. Captive feral pigeons (Columba livia) were offered fonofos-treated seed ad libitum on a test day after a 6 -d period in which one group was given free access to untreated seed and an other group was given no food in one experiment or 15% of normal intake in the other. Avoidance of treated seed reduced intake substantially, preventi ng the ingestion of lethal doses for all birds fed ad libitum and some but not all of the food-restricted birds. Some of the latter regurgitated most of the seed taken in (>60%), reducing by similar to 50% the dose of pestici de assimilated and lowering the dose from above to below lethal levels. Reg urgitation was the most likely explanation for the survival of at least 12 and 50% of the food-restricted birds in these experiments. Regurgitation re duced but did not prevent mortality, because some birds died without regurg itating and others despite doing so. This study provides the first clear ev idence that regurgitation can directly reduce mortality of birds exposed to pesticides in their food. Implications for the risk of poisoning wild bird s and avian toxicity testing are discussed.