Proceedings of the Vertebrate Pest Conference

In 2008, approximately 70 Canada geese were recovered dead in the Moro Cojo Slough area of Monterey County, California. Birds were necropsied and showed signs of abnormal internal bleeding. A total of 37 livers were analyzed for anticoagulants and 36 of these livers contained chlorophacinone. Death was attributable to chlorophacinone poisoning. Two turkey vultures and a barn owl also died, probably as a result of secondary chlorophacinone poisoning. The source of the chlorophacinone was not obvious, as chlorophacinone is used in several different forms on many different crops and also in commensal use. In addition, there often are several days between exposure and death, allowing the movement of the animal from the site of exposure. The ensuing investigations, which lasted several months, suggested that the exposure was due to expanded use of chlorophacinone pellets on artichokes used to control California voles. Subsequently, the label of the rodenticide product was modified to restrict its use when conditions favor goose presence in artichoke fields. No deaths have occurred since the label modification.