Abstract # 167:

Scheduled for Friday, August 18, 2006 07:00 PM-09:00 PM: Session 17 (Regency West 1/3 ) Poster Presentation

Kinematics of Nut-cracking in Wild Capuchin Monkeys in Piaui, Brazil

Q. Liu1, D. Fragaszy1 and K. Simpson2
1University of Georgia, Psychology Department, Athens, GA 30602, USA, 2Kinesiology Department, University of Georgia, Athens, GA 30602, USA
     Wild capuchin monkeys (Cebus libidinosus) in Piaui, Brazil crack palm nuts on hard anvil surfaces (logs and large, flat rocks) using large stones. They do so using remarkably ballistic actions of the entire body and erect bipedal posture. We describe the kinematics of movement and postures achieved during five nut-cracking strikes for each of two adult males and two adult females. Spatial coordinates of 13 anatomical landmarks of the monkey, the estimated center of the nut and a reference location of the anvil were digitized from sagittal plane video (60 Hz; Peak Motus™, v.8.3). Magnitudes and times to maxima/minima and other critical events for linear and angular kinematic quantities were calculated. Monkeys lifted the stone (1440 grams) in a consistent movement sequence, starting from a crouched position with both hands holding the stone, followed by rapid extension of the hips, trunk extension, shoulder flexion to raise the arms/rock, and ending with the rock reaching its peak height. In the downward phase, the monkeys guided the stone to fall onto the nuts. Movements are more strenuous than described for other primate foraging actions and indicate flexible use of postural and manipulative resources. Supported by National Geographic Society (774904).