Human predation and Kloss's gibbon (Hylobates klossii) sleeping trees in Siberut Island, Indonesia

Abstract

Kloss's gibbons (Hylobates Klossii) and Mentawai langurs (Presbytis potenziani) on Siberut Island, Indonesia, both sleep in emergent trees 34-55m tall, situated on crests and upper slopes of hills. They differ in that 91% of gibbon sleeping trees examined were free of lianas, whereas 89% of langur sleeping trees were draped with thick, woody lianas hanging from the branches to the ground. Because indigenous hunters climb lianas to shoot primates in treetops, gibbons are less susceptible than langurs to nocturnal human predation. Hence, the gibbons' preference for-and apparent control of-the limited supply of vineless trees gives them an advantage over langurs.

Knowledge, attitudes and practices of local people on Siberut Island (West-Sumatra, Indonesia) towards primate hunting and conservation

“…Most likely, the species is hunted because of its tendency to enter the people's ladangs to steal crops and as such would be regarded as a pest (Paciulli 2004). This is also well known for the archipelago's southernmost islands, where macaques (and Presbytis) are regularly poisoned with pesticides for this reason (Tenaza 1991). Conversely, the native gibbon is targeted * -corrected by size range of hunting party (see methods for further description), i.e., size between 4-8 people ** -based on Whittaker 2006 by very few hunters, a finding similar to that of Tenaza & Tilson (1985), who reported that despite living at higher densities compared to the three other species, gibbons constituted a mere 4% of the primate skulls counted in the ceremonial houses inside their study area in central Siberut.…”

Sleeping Site Selection by Agile Gibbons: The Influence of Tree Stability, Fruit Availability and Predation Risk

“…trees which were more exposed rather than those that had crowns contiguous with surrounding trees, possibly in response to the presence of clouded leopards and pythons Cheyne /Höing /Rinear /Sheeran (nocturnal predators) at the site. Tenaza and Tilson [1985] found that humans used lianas to gain access to and kill Kloss' gibbons in their sleeping trees. Kloss' gibbons at their site avoided sleeping in trees with lianas, most likely to avoid human predation.…”

“…Reichard [1998] stated that diurnal primates' predation risk is higher at night, so lar gibbons ( H. lar ) reduced their nighttime activities once a sleeping site had been chosen. Kloss' gibbons (H. klossi) avoided sleeping in trees with lianas, perhaps because these provided a substrate for biting ants [Whitten, 1982b;Uhde and Sommer, 2002;Phoonjampa et al, 2010] and enabled predators such as humans and pythons to access sleeping gibbons [Tenaza and Tilson, 1985]. Anderson [1998] posited that large apes prefer nest trees that offer a comfortable place for the night (e.g.…”

“…For arboreal primates, features of a tree such as height, diameter, stability and safety likely influence its suitability for sleeping [Tenaza and Tilson, 1985;Aquino and Encarnación, 1996;Anderson, 1998;Reichard, 1998;Fan and Jiang, 2008;Lutermann et al, 2010;Phoonjampa et al, 2010]. Various external loads and internal stresses act on trees and may affect stability (for more detail, see Mattheck [1994]).…”

“…the primates are protected and engage in specific behaviours to increase security [Anderson, 1984;Tenaza and Tilson, 1985;Anderson, 1998;Reichard, 1998;Anderson, 2000;Fan and Jiang, 2008;Lutermann et al, 2010;Phoonjampa et al, 2010;Cheyne et al, submitted]. Trade-offs may include sharing a space, increased parasite loads and increased risk should the sleeping site be attacked as the primates are grouped [Anderson, 1998[Anderson, , 2000Lutermann et al, 2010].…”