Evidence of Imitation in Trained Gorillas (Gorilla gorilla gorilla).

Imitation is a social learning mechanism in humans but its relevance in nonhuman primates is controversial. Studies have suggested that some ape species, such chimpanzees and orangutans, may be able to imitate. However, records of true imitation in gorillas are scarce. This study was designed to evaluate the imitation ability of two female western lowland gorillas (Gorilla gorilla gorilla) by using the "do as I do" method, after 15 months of training. For the final evaluation, we tested the gorillas with 52 novel actions classified in four categories (Gestures, Object, Object-Object, and Object-Subject). To assess the difficulty of the novel actions, the lead researcher and two independent observers scored the responses from 0 to 3 based on how well they were done. During the training period, the two gorillas obtained similar success rates for imitation. During the evaluation, they achieved true imitation in 46% of transparent actions and 58% of the opaque actions. We identified "Gestures" as the easiest actions for one gorilla and "Object-Subject" for the other. "Object-Object" were the most difficult actions for both gorillas. Our findings show that female western lowland gorillas can imitate after a training period. [ABSTRACT FROM AUTHOR]