Hand use in tufted capuchins (Cebus apella) for extracting a small food item from a tube: digit movements, hand preference and performance

The aim of this study is to analyze the manual patterns used by tufted capuchin monkeys (Cebus apella) to retrieve a small food item from a narrow tube, with special attention focused on the independent use of single fingers, fine digit movements, hand preference and inter-manual differences in the time the monkeys took to obtain the food. Capuchins (n = 20) mainly used their forefinger to extract the food from the tube. The simultaneous use of the index and the middle finger was less frequent, whereas the use of the forefinger in combination with other digits was rare. Capuchins demonstrated a capacity to move single digits independently when the fingers were locating the food inside the tube and displayed a high mobility of the distal phalanx joints. However, they possessed only a limited capacity to coordinate single fingers in space and displayed only a slight degree of manual preshaping when approaching the tube. Hand preference analysis failed to reveal any significant lateral bias for the group: both adults („d 5 years) and immature individuals (< 5 years) of both sexes used either hand with the same frequency. Conversely, latency analysis showed a significant interaction between the subject¡¦s age and performance difference between hands: in adults, but not in immature individuals, the left hand was faster than the right hand in food retrieval.