Use of limestone karst forests by Bornean orangutans (Pongo pygmaeus morio) in the Sangkulirang peninsula, east Kalimantan, Indonesia

The Indonesian province of East Kalimantan is home to some of the largest remaining contiguous tracts of lowland Dipterocarp forest on the island of Borneo. Nest surveys recently conducted in these forests indicated the presence of a substantial population of Eastern Bornean orangutans (Pongo pygmaeus morio) in the Berau and East Kutai regencies in the northern half of the province. The Sangkulirang Peninsula contains extensive limestone karst forests in close proximity to the lowland Dipterocarp forests inhabited by orangutans in these regencies. Orangutans have been sighted in these limestone karst forests, but the importance of this forest type for orangutans has been unclear. Therefore, we conducted 49 km of nest surveys in limestone karst forest to obtain the first quantitative estimates of orangutan densities in this habitat, and walked 28 km of surveys in nearby lowland Dipterocarp forests for comparison. We also gathered basic ecological data along our transects in an attempt to identify correlates of orangutan abundance across these habitat types. Undisturbed limestone karst forests showed the lowest orangutan densities (147 nests/km(2), 0.82 indiv/km(2)), disturbed limestone forests had intermediate densities (301 nests/km(2), 1.40 indiv/km(2)), and undisturbed lowland Dipterocarp forests contained the highest density (987 nests/km(2), 5.25 indiv/km(2)), significantly more than the undisturbed limestone karst forests. This difference was not correlated with variation in liana abundance, fig stem density, or stump density (an index of forest disturbance). Therefore, other factors, such as the relatively low tree species diversity of limestone karst forests, may explain why orangutans appear to avoid these areas. We conclude that limestone karst forests are of low relevance for safeguarding the future of orangutans in East Kalimantan.     

Unexpected Ecological Resilience in Bornean Orangutans and Implications for Pulp and Paper Plantation Management

Ecological studies of orangutans have almost exclusively focused on populations living in primary or selectively logged rainforest. The response of orangutans to severe habitat degradation remains therefore poorly understood. Most experts assume that viable populations cannot survive outside undisturbed or slightly disturbed forests. This is a concern because nearly 75% of all orangutans live outside protected areas, where degradation of natural forests is likely to occur, or where these are replaced by planted forests. To improve our understanding of orangutan survival in highly altered forest habitats, we conducted population density surveys in two pulp and paper plantation concessions in East Kalimantan, Indonesia. These plantations consist of areas planted with fast-growing exotics intermixed with stands of highly degraded forests and scrublands. Our rapid surveys indicate unexpectedly high orangutan densities in plantation landscapes dominated by Acacia spp., although it remains unclear whether such landscapes can maintain long-term viable populations. These findings indicate the need to better understand how plantation-dominated landscapes can potentially be incorporated into orangutan conservation planning. Although we emphasize that plantations have less value for overall biodiversity conservation than natural forests, they could potentially boost the chances of orangutan survival. Our findings are based on a relatively short study and various methodological issues need to be addressed, but they suggest that orangutans may be more ecologically flexible than previously thought.     

The reluctant innovator: orangutans and the phylogeny of creativity

Young orangutans are highly neophobic, avoid independent exploration and show a preference for social learning. Accordingly, they acquire virtually all their learned skills through exploration that is socially induced. Adult exploration rates are also low. Comparisons strongly suggest that major innovations, i.e. behaviours that have originally been brought into the population through individual invention, are made where ecological opportunities to do so are propitious. Most populations nonetheless have large innovation repertoires, because innovations, once made, are retained well through social transmission. Wild orangutans are therefore not innovative. In striking contrast, zoo-living orangutans actively seek novelty and are highly exploratory and innovative, probably because of positive reinforcement, active encouragement by human role models, increased sociality and an expectation of safety. The explanation for this contrast most relevant to hominin evolution is that captive apes generally have a highly reduced cognitive load, in particular owing to the absence of predation risk, which strongly reduces the costs of exploration. If the orangutan results generalize to other great apes, this suggests that our ancestors could have become more curious once they had achieved near-immunity to predation on the eve of the explosive increase in creativity characterizing the Upper Palaeolithic Revolution.     

Apes in space: saving an imperilled orangutan population in Sumatra

Deforestation rates in Sumatra are amongst the highest in the tropics. Lowland forests, which support the highest densities of orangutans, are particularly vulnerable to clearance and fragmentation because they are highly accessible. Consequently, many orangutans will, in the future, live in strictly or partially isolated populations. Whilst orangutans have been extensively studied in primary forests, their response to living in human-dominated landscapes remains poorly known, despite it being essential for their future management. Here, we focus on an isolated group of critically endangered Sumatran orangutans (Pongo abelii) that co-exist with farmers in a mixed agroforest system consisting of degraded natural forest, smallholder (predominantly rubber) farms and oil palm plantations. Over 24 months we conducted the first ever spatial assessment of orangutan habitat use in the human-transformed landscape of Batang Serangan, North Sumatra. From 1,204 independent crop-raiding incidents recorded, orangutans showed strong foraging preference for mixed farmland/degraded forest habitat over oil palm patches. The core home range areas of the eight adult orangutans encompassed only 14% of the available study area. Monthly home range sizes averaged 423 ha (±139, SD) for males, and 131 ± 46 ha for females, and were positively influenced by wild and cultivated fruit presence, and by crop consumption. The average daily distance travelled was similar for both adult males (868 m ± 350, SD) and females (866 m ± 195), but increased when orangutans raided crops. These findings show that orangutans can survive, demographically, in certain types of degraded landscapes, foraging on a mixture of crops and wild fruits. However, the poor quality habitat offered to orangutans by oil palm plantations, in terms of low food availability and as a barrier to female movements, is cause for concern since this is the land use type that is most rapidly replacing the preferred forest habitat across both Sumatran and Bornean orangutan ranges.     

Aerial surveys give new estimates for orangutans in Sabah, Malaysia

Great apes are threatened with extinction, but precise information about the distribution and size of most populations is currently lacking. We conducted orangutan nest counts in the Malaysian state of Sabah (North Borneo), using a combination of ground and helicopter surveys, and provided a way to estimate the current distribution and size of the populations living throughout the entire state. We show that the number of nests detected during aerial surveys is directly related to the estimated true animal density and that a helicopter is an efficient tool to provide robust estimates of orangutan numbers. Our results reveal that with a total estimated population size of about 11,000 individuals, Sabah is one of the main strongholds for orangutans in North Borneo. More than 60% of orangutans living in the state occur outside protected areas, in production forests that have been through several rounds of logging extraction and are still exploited for timber. The role of exploited forests clearly merits further investigation for orangutan conservation in Sabah.     

Orangutan Energetics and the Influence of Fruit Availability in the Nonmasting Peat-swamp Forest of Sabangau,Indonesian Borneo

Data on energy intake and the effects of fluctuations in fruit availability on energy intake for African apes, and orangutans in mast-fruiting habitats, indicate that orangutans may face greater energetic challenges than do their African counterparts. Comparable data on orangutans in nonmasting forests, which experience lower fluctuations in fruit availability, have been lacking, however, complicating interpretations. We conducted a 46-mo study of orangutan energetics in the nonmasting Sabangau peat-swamp forest, Indonesian Borneo. Sabangau orangutans experienced periods of negative energy balance apparently even longer than in mast-fruiting habitats, as indicated by comparisons of observed energy intake with theoretical requirements and analysis of urinary ketones. Daily energy intake was positively related to fruit availability in flanged males, but not in adult females or unflanged males. This may represent different foraging strategies between age-sex classes and suggests that fruit availability is not always an accurate indicator of ape energy intake/balance. Urinary ketone levels were not generally related to fruit availability, daily energy intake, day range, or party size. This is probably due to low energy intake, and consequently high ketone production, throughout much of the study period. Comparisons with published results on African apes support the hypothesis that orangutans are unique among hominoids in regularly experiencing prolonged periods of negative energy balance. This has important effects on orangutan behavior and socioecology, and has likely been a key factor driving the evolutionary divergence of orangutans and African apes.     

Raiders of the lost bark: orangutan foraging strategies in a degraded landscape

Deforestation is rapidly transforming primary forests across the tropics into human-dominated landscapes. Consequently, conservationists need to understand how different taxa respond and adapt to these changes in order to develop appropriate management strategies. Our two year study seeks to determine how wild Sumatran orangutans (Pongo abelii) adapt to living in an isolated agroforest landscape by investigating the sex of crop-raiders related to population demographics, and their temporal variations in feeding behaviour and dietary composition. From focal animal sampling we found that nine identified females raided cultivated fruits more than the four males. Seasonal adaptations were shown through orangutan feeding habits that shifted from being predominantly fruit-based (56% of the total feeding time, then 22% on bark) to the fallback food of bark (44%, then 35% on fruits), when key cultivated resources such as jackfruit (Artocarpus integer), were unavailable. Cultivated fruits were mostly consumed in the afternoon and evening, when farmers had returned home. The finding that females take greater crop-raiding risks than males differs from previous human-primate conflict studies, probably because of the low risks associated (as farmers rarely retaliated) and low intraspecific competition between males. Thus, the behavioral ecology of orangutans living in this human-dominated landscape differs markedly from that in primary forest, where orangutans have a strictly wild food diet, even where primary rainforests directly borders farmland. The importance of wild food availability was clearly illustrated in this study with 21% of the total orangutan feeding time being allocated to feeding on cultivated fruits. As forests are increasingly converted to cultivation, humans and orangutans are predicted to come into conflict more frequently. This study reveals orangutan adaptations for coexisting with humans, e.g. changes in temporal foraging patterns, which should be used for guiding the development of specific human-wildlife conflict mitigation strategies to lessen future crop-raiding and conflicts.     

Variables that influence the activity of captive orangutans

It is well known that the environment significantly influences the behavior of captive animals. However, the specific nature of the cues that promote speciestypical behavior patterns is not usually known. This study extends an earlier investigation by Wilson (Zoo Biology 1: 201–209, 1982). The objective was to identify and quantify specific environmental components that influence activity levels in orangutans. Six enclosure variables were quantified, and activity levels measured, for 29 orangutans housed in nine zoological parks. Multiple regression analysis indicated that the combination of the number of animals, amount of usable surface area, number of movable objects, and enclosure volume was the best predictor of activity levels, accounting for 58% of the variance in activity levels. It was concluded that the provision of large enclosures, containing large numbers of movable objects and providing social opportunities, would promote higher levels of activity in captive orangutans. © 1992 Wiley-Liss, Inc.     

Cooperative Problem Solving by Orangutans (Pongo pygmaeus)

A captive pair of subadult male orangutans (Pongo pygmaeus) performed a cooperative task without training. Both partners had to pull a handle simultaneously in order for each to get food. They also learned the importance of the partner at the apparatus to make a successful response. The requirements of the cooperative task appear to have been understood by the orangutans, much like chimpanzees (Pan troglodytes) in the same situation. In contrast, capuchins (Cebus apella) succeeded in the cooperative task with a limited understanding of the requirement of the task and without taking into account the partner's role. These results gives further support to the hypothesis of a proximity of cognitive processes between chimpanzees and orangutans (in contrast to monkeys) though orangutans have not been seen to hunt cooperatively in the wild.     

Orangutan Nesting Behavior in Disturbed Forest of Sabah,Malaysia: Implications for Nest Census

High concentrations of orangutans remain in the multiple-use forests of the Lower Kinabatangan, Sabah, Malaysia. Compared to primary forest, the habitat is highly fragmented, characterized by a low tree density (332 stems/ha), small tree size (83.6% of trees are <20 m high), low basal area (18 m²/ha), abundance of canopy gaps and high level of soil disturbance. The forest structure and composition influence orangutan nesting patterns, and thus directly influence the results of nest surveys used to determine orangutan population size. In logged forests, tall and large trees are the preferred nesting sites of orangutans. The scarcity of suitable nesting sites in the logged-over forests of Kinabatangan, could partly explain the lower daily rate of nest construction (r = 1.00) versus those of other orangutan populations. The nest decay rate t recorded at the study site (average ± SD = 202 ± 151 days) strongly depends on the species of tree in which a nest is built. Our results illustrate that the nest-related parameters used for orangutan censuses fluctuate among habitat types and emphasize the need to determine specific values of r for specific orangutan populations and of t for different tree species in order to achieve accurate analysis of census data.     

Grouping behavior of Sumatran orangutans (Pongo abelii) and Tapanuli orangutans (Pongo tapanuliensis) living in forest with low fruit abundance

In contrast to the African great apes, orangutans (Pongo spp.) are semisolitary: Individuals are often on their own, but form aggregations more often than expected by chance. These temporary aggregations provide social benefits such as mating opportunities. When fruit availability is high, costs of aggregating should be lower, because competition is less pronounced. Therefore, average party size is expected to be higher when fruit availability is high. This hypothesis would also explain why orangutans in highly fruit-productive habitats on Sumatra are more gregarious than in the usually less productive habitats of Borneo. Here, we describe the aggregation behavior of orangutans in less productive Sumatran habitats (Sikundur and Batang Toru), and compare results with those of previously surveyed field sites. Orangutans in Sikundur were more likely to form parties when fruit availability was higher, but the size of daily parties was not significantly affected by fruit availability. With regard to between-site comparisons, average party sizes of females and alone time of parous females in Sikundur and Batang Toru were substantially lower than those for two previously surveyed Sumatran sites, and both fall in the range of values for Bornean sites. Our results indicate that the assessment of orangutans on Sumatra as being more social than those on Borneo needs revision. Instead, between-site differences in sociality seem to reflect differences in average fruit availability.     

Wild-Born Orangutans (Pongo abelii) Engage in Triadic Interactions During Play

It has long been held that triadic interactions, or interactions between individuals that include shared perception and goals concerning an outside entity, require elaborate cognitive processes such as joint attention. With their connection to shared intentionality, triadic interactions have been a key topic of interest for developmental and evolutionary psychologists, notably when making comparisons between humans and other ape species. There is good evidence that chimpanzees and bonobos engage in triadic interactions; however, convincing evidence for orangutans are more limited and so far have been found only in the context of feeding. I engaged 11 wild-born sanctuary orangutans through the medium of a stick, allowing them to decide how to use the object and how to interact with me. The participating orangutans developed idiosyncratic ways of using the stick and engaging with me during the activity, and six of them alternated their gaze between the stick and me. When I interrupted the activity, the participating orangutans displayed more numerous and different behaviors than before the interruption to actively reengage me in the game. Much like human infants, they appeared more interested in the social interaction than in the stick. These findings confirm that triadic interactions occur in nonenculturated orangutans and are consistent with studies of other nonhuman great ape species, which also show triadic interactions, suggesting that joint attention and potentially shared intentionality may have an early origin in our evolutionary history.     

Reproductive success of two male morphs in a free-ranging population of Bornean orangutans

The reproductive success of male primates is not always associated with dominance status. For example, even though male orangutans exhibit intra-sexual dimorphism and clear dominance relationships exist among males, previous studies have reported that both morphs are able to sire offspring. The present study aimed to compare the reproductive success of two male morphs, and to determine whether unflanged males sired offspring in a free-ranging population of Bornean orangutans, using 12 microsatellite loci to determine the paternity of eight infants. A single flanged male sired most of the offspring from parous females, and an unflanged male sired a firstborn. This is consistent with our observation that the dominant flanged male showed little interest in nulliparous females, whereas the unflanged males frequently mated with them. This suggests that the dominant flanged male monopolizes the fertilization of parous females and that unflanged males take advantage of any mating opportunities that arise in the absence of the flanged male, even though the conception probability of nulliparous females is relatively low.     

Orangutan use of vertical space in an innovative habitat

This study measured use of vertical space in an innovative habitat for three adolescent orangutans (Pongo pygmaeus). The indoor habitat was innovative in two main ways: a flooded floor and retractable skylights. It included four large molded trees and interwoven vines throughout 1,620 m³ of space. The exhibit was divided into four vertical levels: skylights, upper canopy, lower canopy, and flooded floor. Five trained observers made instantaneous scans of the exhibit every 5 minutes, in 1‐hour blocks of time over a 10‐month period, logging 180 hours of observations. One location (of 55) and one behavior (of 53) were noted at each interval. Behaviors were collapsed to form five categories: solitary inactivity, solitary activity, social inactivity, social activity, and eating/drinking. Results showed the orangutans favored the upper canopy, which contained many tree limbs for sitting and reclining. The orangutans next favored the lower canopy and the skylights, especially those skylights that were out of public view. The habitat’s flooded floor was avoided (they used it just 1% of the time), as planned by the exhibit designers who intended to showcase these arboreal primates in trees, not on the ground. When compared with wild orangutans, we considered few of their behaviors to be atypical: foraging/eating plastic (vines) and stereotyped behaviors. Overall, the unique design of the habitat provided opportunities for a range of species‐typical behaviors, varying by vertical level, demonstrating the importance of providing sufficient vertical space for orangutans. Zoo Biol 19:239–251, 2000. © 2000 Wiley‐Liss, Inc.     

Food Neophobia and Social Learning Opportunities in Great Apes

Finding food resources and maintaining a balanced diet are major concerns for all animals. A compromise between neophobia and neophilia is hypothesised to enable animals to enlarge their diet while limiting the risk of poisoning. However, little is known about how primates respond to novel food items and whether their use is socially transmitted. By comparing how four different species of great apes respond to novel food items, we investigated how differences in physiology (digestive tract size and microbial content), habitats (predictability of food availability), and social systems (group size and composition) affect their response toward novelty. We presented two familiar foods, one novel fruit, four novel aromatic plants from herbal medicine, and kaolin to captive chimpanzees (Pan troglodytes), western gorillas (Gorilla gorilla), Bornean orangutans (Pongo pygmaeus) and Sumatran orangutans (Pongo abelii). We recorded smelling, approach-taste delays, ingestion, interindividual observations, and food transfers with continuous sampling. We found that behaviors differed between the apes: chimpanzees were the most cautious species and observed their conspecifics handling the items more frequently than the other apes. Close observations and food transfers were extremely rare in gorillas in comparison to orangutans and chimpanzees. We suggest that a low neophobia level reflects an adaptive response to digestive physiological features in gorillas and to unpredictable food availability in orangutans. Social interactions appeared to be predominant in chimpanzees and in both orangutan species to overcome food neophobia. They reflect higher social tolerance and more opportunities for social learning and cultural transmission in a feeding context.     

Comparing the performances of apes (Gorilla gorilla, Pan troglodytes, Pongo pygmaeus) and human children (Homo sapiens) in the floating peanut task

Recently, Mendes et al. [1] described the use of a liquid tool (water) in captive orangutans. Here, we tested chimpanzees and gorillas for the first time with the same "floating peanut task." None of the subjects solved the task. In order to better understand the cognitive demands of the task, we further tested other populations of chimpanzees and orangutans with the variation of the peanut initially floating or not. Twenty percent of the chimpanzees but none of the orangutans were successful. Additional controls revealed that successful subjects added water only if it was necessary to obtain the nut. Another experiment was conducted to investigate the reason for the differences in performance between the unsuccessful (Experiment 1) and the successful (Experiment 2) chimpanzee populations. We found suggestive evidence for the view that functional fixedness might have impaired the chimpanzees' strategies in the first experiment. Finally, we tested how human children of different age classes perform in an analogous experimental setting. Within the oldest group (8 years), 58 percent of the children solved the problem, whereas in the youngest group (4 years), only 8 percent were able to find the solution.     

Determinants of orangutan density in the dryland forests of the Leuser Ecosystem

Orangutans are the only great ape in Asia. Since orangutan densities vary between habitat types within regions and within similar habitat types among regions, it is important to determine areas with high densities for their protection. In this paper we show that orangutan density in old-growth dryland forests in the Leuser Ecosystem, Sumatra is significantly related to the density of large strangling figs and topsoil pH. In addition, large fig density depends on topsoil pH. Provided that orangutans are present and no hunting or logging occur, topsoil pH seems a promising method for rapid assessment of potential orangutan density over large areas.     

Factors Affecting Mortality,Fertility, and Well-being in Relation to Species Differences in Captive Orangutans

For the past 20 years, field biologists have recognized Sumatran and Bornean orangutans as belonging to 2 separate subspecies. Primatologists have recently suggested that they may be full species and that the Bornean species could be divided into 3–5 subspecies. Statistical analyses of factors affecting the mortality, fertility, and well-being of captive orangutans have revealed some important differences between Bornean, Sumatran, and hybrid orangutans that could support the suggestion. Hybrid orangutans appeared to be genetically weaker, with much lower survival rates than pure subspecific individuals. The weakness also may have contributed to their higher rate of infant rejection. In addition, infertility was 3 times higher in Bornean orangutans than in Sumatran and hybrid orangutans.     

Forest Structure and Support Availability Influence Orangutan Locomotion in Sumatra and Borneo

The influence of habitat structure and support availability on support use is an important aspect of understanding locomotor behavior in arboreal primates. We compared habitat structure and support availability in three orangutan study sites—two on Sumatra (Pongo abelii) in the dry‐lowland forest of Ketambe and peat swamp forest of Suaq Balimbing, and one on Borneo (Pongo pygmaeus wurmbii) in the disturbed peat swamp forest of Sabangau—to better understand orangutan habitat use. Our analysis revealed vast differences in tree and liana density between the three sites. Sabangau had a much higher overall tree density, although both Sumatran sites had a higher density of larger trees. The two peat swamp forests were more similar to each other than to Ketambe, particularly with regard to support availability. Ketambe had a wider variety of supports of different sizes and types, and a higher density of larger lianas than the two peat swamps. Orangutans in all three sites did not differ substantially in terms of their preferred supports, although Sumatran orangutans had a strong tendency to use lianas, not observed in Sabangau. Differences in observed frequencies of locomotor behavior suggest the homogeneous structure of Sabangau limits the locomotor repertoire of orangutans, with high frequencies of fewer behaviors, whereas the wider range of supports in Ketambe appears to have facilitated a more varied locomotor repertoire. There were no differences among age‐sex classes in the use of arboreal pathways in Suaq Balimbing, where orangutans selected larger trees than were typically available. This was less apparent in Sabangau, where orangutans generally used trees in relation to their environmental abundance, reflecting the homogeneous nature of disturbed peat swamp forest. These results demonstrate that forest architecture has an important influence on orangutan locomotion, which may become increasingly important as the structure of orangutan habitat continues to be altered through human disturbance. Am. J. Primatol. 74:1128‐1142, 2012. © 2012 Wiley Periodicals, Inc.     

Social organization and the evolution of cumulative technology in apes and hominins

Culturally supported accumulation (or ratcheting) of technological complexity is widely seen as characterizing hominin technology relative to that of the extant great apes, and thus as representing a threshold in cultural evolution. To explain this divide, we modeled the process of cultural accumulation of technology, which we defined as adding new actions to existing ones to create new functional combinations, based on a model for great ape tool use. The model shows that intraspecific and interspecific variation in the presence of simple and cumulative technology among extant orangutans and chimpanzees is largely due to variation in sociability, and hence opportunities for social learning. The model also suggests that the adoption of extensive allomaternal care (cooperative breeding) in early Pleistocene Homo, which led to an increase in sociability and to teaching, and hence increased efficiency of social learning, was enough to facilitate technological ratcheting. Hence, socioecological changes, rather than advances in cognitive abilities, can account for the cumulative cultural changes seen until the origin of the Acheulean. The consequent increase in the reliance on technology could have served as the pacemaker for increased cognitive abilities. Our results also suggest that a more important watershed in cultural evolution was the rise of donated culture (technology or concepts), in which technology or concepts was transferred to naïve individuals, allowing them to skip many learning steps, and specialization arose, which allowed individuals to learn only a subset of the population's skills.