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

Abstract

AbstractRegurgitation 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 another group was given no food in one experiment or 15% of normal intake in the other. Avoidance of treated seed reduced intake substantially, preventing 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 ∼50% the dose of pesticide assimilated and lowering the dose from above to below lethal levels. Regurgitation was the most likely explanation for the survival of at least 12 and 50% of the food‐restricted birds in these experiments. Regurgitation reduced but did not prevent mortality, because some birds died without regurgitating and others despite doing so. This study provides the first clear evidence that regurgitation can directly reduce mortality of birds exposed to pesticides in their food. Implications for the risk of poisoning wild birds and avian toxicity testing are discussed.