Positional Behavior of Delacour's Langurs (Trachypithecus delacouri) in Northern Vietnam
Information on positional behavior can help elucidate relationships between a species' morphology, behavior, and environment. Delacour's langurs (Trachypithecus delacouri) are similar to other colobines in body mass and intermembral index, yet inhabit a limestone karst environment. From August 2007 to July 2008, we collected 372 h of positional behavior and substrate use data from 8 groups of Trachypithecus delacouri in Van Long Nature Reserve, Vietnam to address questions about how the distinct -and potentially dangerous- features of karst influence colobine positional behavior. Results show that Trachypithecus delacouri is predominantly quadrupedal (66%). However, they exhibit differences that set them apart from many other colobines. Nearly 80% of locomotor and postural behaviors were performed on rocks. Leaping was remarkably infrequent, representing only 6% of overall locomotion. They leapt 3 times more frequently on trees (13%) than on rocks (4%) and more frequently used trees as a landing substrate than rocks (38% vs. 23%), both significant differences. We argue that rock (and cliff) travel is altogether different from terrestrial and arboreal travel and propose using the term petrous to indicate the substrate and incorporate the implications of its precise sharpness and verticality that lead to the complexities and risk of locomotion on rock surfaces. Trachypithecus delacouri does not show specific adaptations for limestone karst. Instead they appear to be a behaviorally flexible species and, owing to the generalized locomotor capabilities that characterize cercopithecids, capable of locomoting through and living in the limestone rock environment to which they have relatively recently been restricted. © 2011 Springer Science+Business Media, LLC.
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