Hand preference for a bimanual coordinated task in captive hatinh langurs (Trachypithecus hatinhensis) and grey-shanked douc langurs (Pygathrix cinerea)

•We evaluated hand preferences in hatinh and grey-shanked douc langurs for the first time.•Both species present clear individual lateralisation.•No group level hand preferences were detected.•The strength of hand preferences was greater in hatinh than in douc langurs.•No sex differences were detected within species. 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.