Locomotor Kinematics of Two Semi-Wild Macaque Species (Macaca assamensis and Macaca arctoides) in Thailand.

ABSTRACT

This project aimed to investigate primate locomotor kinematics noninvasively in the wild. Semi-wild Assamese and stump-tailed macaques were selected for the study, which was performed in Thailand. We investigated their locomotor kinematics and its relationship to habitat use. The macaques' positional behavior was recorded with two video cameras, and kinematic parameters were estimated during terrestrial quadrupedal locomotion, using the markerless method. The data analyzed so far revealed that stump-tailed macaques walk with longer, less frequent strides than Assamese macaques. Although stump-tailed macaques present a smaller angular excursion of the shoulder joint than Assamese macaques, they exhibited a relatively large shoulder girdle motion and anteroposterior translation of the shoulder, which increased their stride length. Additionally, stump-tailed macaques exhibited a digitigrade gait and elbow extension, suggesting a good adaptation to terrestrial locomotion. Assamese macaques, on the other hand, exhibited a gait that did not seem optimized for terrestrial locomotion, using the hands in a palmigrade posture and frequently flexing the fingers at varying degrees. The kinematic characteristics of the two species studied is consistent with previous field observations reporting that Assamese macaques are highly arboreal, whereas stump-tailed macaques are more terrestrial.