Opportunistic behaviour or desperate measure? Logging impacts may only partially explain terrestriality in the Bornean orang-utan Pongo pygmaeus morio

Abstract

There is a lack of information on how the Endangered Bornean orang-utan Pongo pygmaeus morio moves through its environment. Here we report on a camera-trapping study carried out over 2.5 years to investigate the orang-utan's terrestrial behaviour in Wehea Forest, East Kalimantan, Indonesia. We set 41 camera trap stations in an area of secondary forest, 36 in recently logged forest immediately adjacent to Wehea Forest, and 20 in an area of primary forest in the heart of Wehea Forest. A combined sampling effort of 28,485 trap nights yielded 296 independent captures of orang-utans. Of the three study sites, orang-utans were most terrestrial in recently logged forest, which may be only partially explained by breaks in the canopy as a result of logging activity. However, orang-utans were also terrestrial in primary forest, where there was a closed canopy and ample opportunity for moving through the trees. Our results indicate that orang-utans may be more terrestrial than previously thought and demonstrate opportunistic behaviour when moving through their environment, including using newly constructed logging roads for locomotion, possibly indicating some degree of resilience to human disturbance. This finding is important because of the potential role of sustainably logged forests for orang-utan conservation.

Neck function in early hominins and suspensory primates: Insights from the uncinate process

“…In addition to suspensory postures, the great ape behavioral repertoire includes a significant terrestrial component, including bouts of bipedal walking (Crompton, Vereecke, & Thorpe, ). Even when the effects of intensive logging are controlled for, both male and female Pongo naturally engage in habitual terrestrial locomotion (Ancrenaz et al, ; Loken, Boer, & Kasyanto, ; Loken, Spehar, & Rayadin, ). Although roughly 80% of locomotor behavior in Pongo is performed in suspension (Cant ), unlike the mode of true brachiation in Hylobates , Pongo most often employs two unique suspensory‐related locomotor modes known as “clamber” and “sway” to locomote (Cant, ; Hunt, ).…”

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

“…Three recent studies have sought to investigate and quantify orangutan terrestrial behavior using indirect observation through ground‐level camera traps. Loken et al [], Ancrenaz et al [], and Loken et al [] reported frequent detection by camera traps of Bornean orangutans on the ground at several sites, including varying types of forest subjected to varying degrees of human disturbance. These camera‐trap studies have convincingly shown that in the absence of human observers, (flanged) males use the ground rather frequently.…”

“…These camera‐trap studies have convincingly shown that in the absence of human observers, (flanged) males use the ground rather frequently. However, the other age‐sex classes were also recorded to be on the ground, albeit less frequently in most [Ancrenaz et al, ; Loken et al, ], but not all sites [Loken et al, ].…”

Comparing spatial capture–recapture modeling and nest count methods to estimate orangutan densities in the Wehea Forest, East Kalimantan, Indonesia

“…Orangutans do not have unique stripe patterns or markings, but individuals are identifiable based on facial characteristics and other features that can be recognized from photographs. Secondly, recent studies indicate that Bornean orangutans may move on the ground more than previously thought, although Sumatran orangutans seem to engage in terrestrial behavior less often, perhaps because of the presence of a potential terrestrial predator, the tiger (Loken et al, 2013(Loken et al, , 2015Ancrenaz et al, 2014). This increases the likelihood of capture by camera traps for at least Bornean orangutans.…”

“…Despite its promise and wide application in wildlife studies, camera trapping has only recently been embraced by primatologists (Head et al, 2012;Olson et al, 2012;Tan et al, 2013;Loken et al, 2013Loken et al, , 2015Galvis et al, 2014;Gregory et al, 2014). Most notably, a recent study simultaneously used nest surveys and camera trapping to estimate the relative abundance and distribution of chimpanzees (Pan troglodytes troglodytes) and gorillas (Gorilla gorilla gorilla) across different habitat types in West Africa, and found that the two methods produced roughly comparable results (Nakashima et al, 2013).…”