One-trial long-lasting food-aversion learning in wild Japanese monkeys (Macaca fuscata)

We examined how Japanese monkeys in the wild formed an aversion to food which had been paired with poison. Ten monkeys of various ages and both sexes were chosen as subjects from 105 members of the Shiga-A1 troop at Jigokudani in Shiga Heights in Japan. We gave almond nuts to each subject. Once a monkey ate 10-20 almond nuts, he was captured and moved into an injection cage. Seven experimental subjects were injected intravenously with cyclophosphamide (20 mg/kg). Three control subjects received the same treatment except that they were injected with physiological saline. About 1 hour later, all subjects were released into the troop. The tests for conditioned aversions were conducted during the next 2 days. In the tests, the experimental subjects would not eat almond nuts, while the control subjects showed no hesitation in eating them. Five of the seven experimental subjects retained perfectly the aversion to almond nuts in tests conducted 1 month and 3 months later. The one-trial long-lasting food-aversion learning shown by the wild Japanese monkeys is discussed in terms of their feeding strategy. These results also suggest that food-aversion conditioning has potential as a nonlethal method for controlling crop-raiding monkeys.