Right-handedness in humans reflects the functional brain specialisation of the left hemisphere. To better understand the origins of this population-level tendency, it is crucial to understand manual lateralisation in other non-human primate species. The aim of this article is to present a first approach to the hand preference of two primates from Vietnam, the endangered hatinh langur (Trachypithecus hatinhensis) and the critically endangered grey-shanked douc langur (Pygathrix cinerea). Eighteen individuals from each species (N = 36) were evaluated by means of the bimanual coordinated tube task and their responses were recorded in terms of manual events and bouts. Our results showed that subjects presented strong individual-level preferences but not lateralisation at the group-level. No sex differences were detected within species. The index finger was used in all of the extractions during this bimanual task, alone (86 %) or in combination with other fingers (14 %). In addition, hatinh langurs exhibited a greater strength of hand preferences than grey-shanked douc langurs, pointing to a possible higher manual specialisation during the leaf-eating process. These findings help to broaden our scarce knowledge of manual laterality in Asian colobine monkeys and confirm the bimanual tube task as a sensitive measure for assessing manual laterality in non-human primates.

人类的惯用右手反映了左半球的大脑功能。为了更好地了解这种种群水平趋势的起源，了解其他非人类灵长类物种的人工侧枝化至关重要。本文的目的是针对来自越南的两个灵长类动物，即濒危的Hatinh叶猴（Trachypithecus hatinhensis）和极度濒临灭绝的灰胫杜克叶猴（Pygathrix cinerea）的手部偏爱提出第一种方法。）。通过双向协调管任务评估了来自每个物种的18个个体（N = 36），并根据手动事件和回合记录了他们的反应。我们的结果表明，受试者表现出强烈的个人偏好，但在团体层面没有偏向。在物种内未检测到性别差异。在此双向任务中，食指单独（86％）或与其他手指（14％）组合用于所有提取中。此外，哈蒂叶猴的手型喜好度高于灰柄杜克叶猴，这表明在叶食过程中可能需要更高的手工专业化水平。