Terrestrial Positional Behavior of Wild Pongo pygmaeus.

Area of Science:

• Primatology
• Behavioral Ecology
• Biomechanics

Background:

• Orangutan (Pongo pygmaeus) terrestrial behavior is largely unstudied in the wild, with most research conducted in captivity.
• Understanding wild orangutan ground movement is crucial for comprehending their ecological niche and evolutionary adaptations.

Purpose of the Study:

• To investigate the terrestrial locomotor and postural behavior of wild orangutans (Pongo pygmaeus) on natural substrates.
• To provide the first assessment of wild orangutan ground-based positional behavior using camera-trap data.

Main Methods:

• Utilized motion-activated camera footage collected over five years in Gunung Palung National Park, Indonesia.
• Analyzed 100 instances of wild orangutan terrestrial activity, documenting hand/foot postures, locomotion patterns, and hindlimb joint movements.
• Qualitatively assessed orthograde behaviors and hindlimb joint excursions.

Main Results:

• Wild orangutans predominantly used quadrupedal fist-walking with heel-strike for terrestrial locomotion.
• Individuals frequently adopted upright (bipedal/monopedal) postures with fully extended hips and knees.
• Variability in wrist position and overstride patterns was observed during quadrupedal locomotion.

Conclusions:

• Wild orangutan terrestrial locomotion involves fist-walking and upright postures, mirroring arboreal adaptations.
• The observed bipedalism on the ground is consistent with their arboreal locomotion, featuring full hindlimb extension.
• Asymmetrical limb movements suggest intrinsic positional adaptability in orangutans, independent of substrate type.