Why do orangutans leave the trees? Terrestrial behavior among wild Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan, Central Kalimantan

Orangutans (genus Pongo) are the largest arboreal mammals, but Bornean orangutans (P. pygmaeus spp.) also spend time on the ground. Here, we investigate ground use among orangutans using 32,000 hr of direct focal animal observations from a well‐habituated wild population of Bornean orangutans (P. p....

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Published in:American journal of primatology 2015-11, Vol.77 (11), p.1216-1229
Main Authors: Ashbury, Alison M., Posa, Mary Rose C., Dunkel, Lynda P., Spillmann, Brigitte, Atmoko, S. Suci Utami, van Schaik, Carel P., van Noordwijk, Maria A.
Format: Article
Language:English
Subjects:
Age Factors
Animal behavior
Animals
Behavior, Animal
Borneo
camera trapping
direct observation
Drinking
Ecosystem
Feeding Behavior
Female
ground travel
Indonesia
Isoptera
Locomotion
Male
Monkeys & apes
orangutan terrestriality
Pongo pygmaeus
Pongo pygmaeus - physiology
Pongo pygmaeus wurmbii
Sex Factors
Studies
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Summary:Orangutans (genus Pongo) are the largest arboreal mammals, but Bornean orangutans (P. pygmaeus spp.) also spend time on the ground. Here, we investigate ground use among orangutans using 32,000 hr of direct focal animal observations from a well‐habituated wild population of Bornean orangutans (P. p. wurmbii) living in a closed‐canopy swamp forest at Tuanan, Central Kalimantan, Indonesia. Ground use did not change with increasing observation time of well‐habituated individuals, suggesting it was not an artifact of observer presence. Flanged males spent the most time on the ground (ca. 5% of active time), weaned immatures the least (around 1%). Females and immatures descended mainly to feed, especially on termites, whereas flanged males traveled more while on the ground. Flanged males may travel more inconspicuously, and perhaps also faster, when moving on the ground. In addition, orangutans engaged in ground‐specific behavior, including drinking from and bathing in swamp pools. Supplementary records from 20 ground‐level camera traps, totaling 3986 trap days, confirmed the observed age‐sex biases in ground use at Tuanan. We conclude that ground use is a natural part of the Bornean orangutan behavioral repertoire, however it remains unclear to what extent food scarcity and canopy structure explain population differences in ground use. Am. J. Primatol. 77:1216–1229, 2015. © 2015 Wiley Periodicals, Inc.
ISSN:0275-2565
1098-2345
DOI:10.1002/ajp.22460