An experimental study of nettle feeding in captive gorillas.

Mountain gorillas (Gorilla beringei beringei) in Karisoke, Rwanda, feed on the stinging nettle Laportea alatipes by means of elaborate processing skills. Byrne [e.g. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 358:529-536, 2003] has claimed that individuals acquire these skills by means of the so-called program-level imitation, in which the overall sequence of problem-solving steps (not the precise actions) is reproduced. In this study we present western lowland gorillas (Gorilla gorilla gorilla) with highly similar nettles. Twelve gorillas in three different groups (including also one nettle-naïve gorilla) used the same program-level technique as wild mountain gorillas (with differences mainly on the action level). Chimpanzees, orangutans, and bonobos did not show these program-level patterns, nor did the gorillas when presented with a plant similar in structural design but lacking stinging defenses. We conclude that although certain aspects (i.e. single actions) of this complex skill may be owing to social learning, at the program level gorilla nettle feeding derives mostly from genetic predispositions and individual learning of plant affordances.