True imitation in marmosets

Marmosets, Callithrix jacchus, observed a demonstrator removing the lids from a series of plastic canisters to obtain a mealworm. When subsequently allowed access to the canisters, marmosets that observed a demonstrator using its hands to remove the lids used only their hands. In contrast, marmosets that observed a demonstrator using its mouth also used their mouth to remove the lids. Since hand and mouth demonstrators brought about identical changes in the canisters, the differential test behaviour of the observer groups suggests that they learned about the demonstrator's behaviour. Furthermore, marmosets that had not been given the opportunity to observe a demonstrator prior to testing had a low probability of mouth opening, even if the canisters were previously opened by a mouth-opening demonstrator in an olfactory control experiment. Corroborating Bugnyar & Huber's (1997, Animal Behaviour, 54, 817-831) earlier findings, our results provide further evidence that marmosets can imitate. (C) 2000 The Association for the Study of Animal Behaviour.