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Free keywords:
dexterity, feeding skill, gorillas, great ape, manipulative behaviour, precision grip, thumb
Abstract:
Although gorillas rarely use tools in the wild, their manipulative skills during plant processing may be similar to those of other tool-using great apes. Virunga mountain gorillas (Gorilla beringei beringei) are known for the complexity in their methods of thistle and nettle plant preparation in the wild. However, there are no comparable data on food processing in the population of mountain gorillas from the Bwindi Impenetrable National Park, Uganda. We investigated the manual actions and hand grips used when accessing edible parts of two hard-to-process plants defended by stinging hairs, epidermis or periderm (i.e. peel of Urera hypselodendron and pith of Mimulopsis arborescens), and one undefended plant (i.e. leaves of Momordica foetida) in 11 Bwindi wild mountain gorillas using video records ad libitum. Similar to thistle feeding by Virunga gorillas, Bwindi gorillas used the greatest number of manual actions for the most hard-to-process plant (U. hypselodendron), and the actions were ordered in several key stages and organized hierarchically. The demands of processing plant material elicited 19 different grips and variable thumb postures, of which three grips were new and 16 grips have either been previously reported or show clear similarities to grips used by other wild and captive African apes and by humans. Moreover, our study only partly supports a functional link between diet and hand morphology in mountain gorillas and suggests that the gorilla hand is best adapted to forceful grasping that is required for both manipulation and arboreal locomotion.
