Abstract

Behavioural tradition has been an active topic in animal behaviour since the renowned Japanese macaque studies of half a century ago, yet controlled field experiments to clearly identify social learning began only recently. In a field experiment inspired by this famous food cleaning study we found that naïve infants copy in details how their mother handle sandy fruits. Then we used an established laboratory experimental paradigm, employing ‘artificial fruits’ to test for copying of different actions by wild vervet monkeys. We demonstrated social learning from high ranking female models as well as matching of the movement used to access the reward inside. In another experiment, we show that vervet monkeys will abandon personal foraging preferences in favour of group norms new to them. Groups first learned to avoid the bitter-tasting alternative of two foods. Presentations of these options untreated revealed all new naïve infants adopting maternal preferences. Males migrating between groups where the alternative food was eaten switched to the new local norm. Observing two group splits of low-ranking females we found significant change in their foraging preference, converging on that of the previous dominant monkeys in their origin group, demonstrating how biased transmission may lead to population level traditions.