SENSORIMOTOR COGNITION IN YOUNG FERAL ORANGUTANS (PONGO-PYGMAEUS)

The goal of this study was to describe object manipulation in wild orangutan infants and juveniles. Object manipulation is an important subsistence activity that also reflects cognitive functioning. Orangutans were studied in the field, at the Tanjung Puting Reserve, Kalimantan Tengah, 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 555 hr and for an average of three full dawn-to-dusk ''follows'' each. Young orangutan's manipulations were categorized along a hierarchy of complexity. The least complex manipulations were single sensorimotor actions such as grasping, mouthing, and waving. The most complex manipulations were combinations and coordinations of actions, such as experimentation with objects, tool use, and planning. Manipulative behavior occurred mainly when foraging, i.e. when obtaining and processing food items. Interestingly, complex behavior occurred most often when locomoting. The most complex object manipulations, however, occurred rarely. Infants and juveniles exhibited equivalent levels of complexity. Several 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. This study also highlights the cognitive abilities of young wild orangutans regarding tool use.