The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

How do wild gibbons decide where to sleep?


Anthropology, Southern Illinois University

Thursday 3:15-3:30, Galleria South Add to calendar

Where animals choose to sleep depends on a variety of behavioral and ecological factors. Despite sufficient quantitative data on factors defining sleeping site choices, predation avoidance is often regarded superior over food access, avoiding parasites, comfort, and range/resource defense. With a comparative approach, we tested all hypotheses for the selection of sleeping sites in four wild white-handed gibbon groups (Hylobates lar) at Khao Yai National Park, Thailand. From July-November 2010, we recorded 59 sleeping trees for ten adult individuals. The food access hypothesis was supported by a significantly shorter travel distance between the last important feeding tree and the sleeping tree compared to the average distance traveled between important feeding trees visited that day, defined retrospectively as trees in which the gibbons fed longer than the average duration in other important feeding trees. Likewise, they fed significantly longer in the last important source compared to other important sources of that day. The predation avoidance hypothesis was supported by the selection of concealed sleeping locations within trees and cryptic behavior prior to retiring. Defecation never occurred at a sleeping tree, and individuals were at significantly lower heights during defecations than while engaged in other activity perhaps to avoid parasite contamination. We conclude that the selection of sleeping sites in white-handed gibbons is multi-functional. Individuals choose sleeping trees strategically to primarily maximize access to important food trees and avoid predators while factors like comfort and parasite avoidance may also influence where gibbons spend the night.

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