SENSORIMOTOR COGNITION IN YOUNG FERAL ORANGUTANS (PONGO-PYGMAEUS)

The goal of this study was to describe object manipulation in wild ora ngutan infants and juveniles. Object manipulation is an important subs istence activity that also reflects cognitive functioning. Orangutans were studied in the field, at the Tanjung Puting Reserve, Kalimantan T engah, Indonesia. Fourteen orangutans, grouped by age (infants 2.5 to 4.6 years; juveniles 5 to 8.5 years), were observed over a total of 55 5 hr and for an average of three full dawn-to-dusk ''follows'' each. Y oung orangutan's manipulations were categorized along a hierarchy of c omplexity. The least complex manipulations were single sensorimotor ac tions such as grasping, mouthing, and waving. The most complex manipul ations were combinations and coordinations of actions, such as experim entation with objects, tool use, and planning. Manipulative behavior o ccurred mainly when foraging, i.e. when obtaining and processing food items. Interestingly, complex behavior occurred most often when locomo ting. The most complex object manipulations, however, occurred rarely. Infants and juveniles exhibited equivalent levels of complexity. Seve ral aspects of this study point to the importance of social assistance provided by competent mothers for the development of young orangutans ' ability to locomote and to locate, obtain, and process food items. T his study also highlights the cognitive abilities of young wild orangu tans regarding tool use.