Imitation in free-ranging rehabilitant orangutans (Pongo pygmaeus).

We made an observational study of spontaneous imitation in orangutans (Pongo pygmaeus). Previous studies may have underestimated great apes' imitative capacities by studying subjects under inhibiting conditions. We used subjects living in enriched environments, namely, rehabilitation. We collected a sample of spontaneous imitations and analyzed the most complex incidents for the likelihood that true imitation, learning new actions by observing rather than by doing, was involved in their acquisition. From 395 hr of observation and other reports on 26 orangutans, we identified 354 incidents of imitation. Of these, 54 complex incidents were difficult to explain by forms of imitation based on associative processes grounded in experimental learning alone; they were, however, congruent with acquisition processes that include true imitation. These findings suggest that orangutans may be capable of true imitation and point to critical eliciting factors.