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Among known mammals, orangutans have the longest period of dependence and exclusive association between mother and offspring before a younger sibling is born. Comparison of available data on wild Sumatran and Bornean orangutans reveals a similar development of essential survival skills up to c. 5 years of age, but among Bornean orangutans earlier complete weaning and start of independent ranging through cessation of the association between mother and offspring, despite reported higher food availability in Sumatra. It is suggested that this difference is related to the assumed difference in main cause of mortality: starvation during irregular periods of widespread drought in Borneo vs predation in Sumatra. The benefits of association to both mother and offspring are likely to be different under these different selection pressures. To understand fully the differences between and variation among Bornean and Sumatran orangutans more high quality long-term demographic data on several populations are needed.

This chapter examines spontaneous innovation in orangutans using prevalence-based methods for identifying potential innovations in free-ranging populations and comparisons between rehabilitant and wild orangutans. Aims were to update the list of innovations, validate potential wild innovations, and estimate the innovative processes involved. Findings derive from systematic observations at one wild orangutan site (Tuanan) and four rehabilitant sites plus findings from eight other wild orangutan sites. Wild orangutan evidence identified 56 potential innovations. Validation using rehabilitant data suggests dropping some entries, adding others, and lumping or splitting others. An approximation on what was innovated was made by comparing potential wild innovations with similar species-typical and rehabilitant variants. These comparisons suggest that orangutans innovate by making small extensions to existing skills: combining old skills in new ways, adding a tool, applying old skills to new functions, and changing the items used. All are consistent with findings on great ape intelligence.

Projects for rehabilitating then releasing ex-captive orangutans to free forest life have operated continuously, throughout the orangutan’s modern range, on both Borneo and Sumatra, since the 1960s. This chapter assesses the role of rehabilitation in the conservation of orangutan populations in their natural habitat in light of over 40 years of operation. The chapter reviews the history of orangutan rehabilitation efforts, including its priorities, politics, and practicalities relative to conservation. The chapter also reviews available empirical data on survival rates, activity budgets, diet, and reproduction in an effort to assess the success of orangutan rehabilitation empirically, as a basis for responding to persistent criticisms that orangutan rehabilitation is not successful and does not contribute to conservation. Finally, the chapter discusses how orangutan rehabilitation operates today, as a basis for understanding the complexities involved, modern approaches to programming, remaining limitations, and continuing challenges.

This chapter provides an overview of the sounds and vocalizations that Sumatran and Bornean orangutans produce. The current data set indicates that there are at least 32 different orangutan sounds and vocalizations that can be distinguished. Interestingly enough not all of these are produced by all individuals in all populations and several occur only in certain populations, but not in others. These preliminary findings indicate that there might be socially learned variation in orangutan sounds and that the cultural domain includes sounds. Future studies should examine such possibilities in detail.

Knowledge of the density and distribution of the endangered orangutan is essential both for their conservation and to identify ecological factors that limit their population size. The authors of this chapter collated orangutan density estimates from 110 locations throughout their range, standardized these for differences in survey design and categorized each location using broad descriptions of the habitats present and the degree of logging disturbance. They found that orangutan density is higher in Sumatra than Borneo, as expected, but found no difference in density between subspecies in Borneo, which suggests that Pongo pygmaeus morio has evolved adaptations to cope with food scarcity in eastern Borneo. The authors of this chapter found support for the hypothesis that orangutan densities are higher in sites with less extreme periods of food shortage, by demonstrating that sites with a mosaic of different habitat types support significantly higher densities than those with only a single habitat type present. Orangutan density declines significantly with altitude in Borneo but the authors of this chapter did not find this relationship for Sumatra, although this may be due to other underlying factors. Heavy logging disturbance has a severe negative effect on density but light logging carried out by well-managed selective logging operations appears to have no effect on orangutan density. The chapter discusses the implications of these findings for orangutan conservation.

Good health results from homeostasis: the balancing, through continuous interaction, of an organism’s myriad dynamic physiological processes. Parasitology allows us to gain important information not only about the types of parasites which are infecting individuals but also about their general condition. By comparing the health of wild and semi-wild orangutans, at different sites under varying degrees of human pressure, this chapter builds a picture of the factors affecting health in these two equally important populations. Our unique approach enables us to investigate whether complex aspects of ethology and ecology influence parasite infections and how parasites may have an impact on whole ecosystems, out of all proportion to their relative size. It is hoped that these efforts will lead to an improved understanding of how best to promote the long-term survival of all orangutans.

Recent comparative work has claimed the presence of socially transmitted behavioral innovations, ranging from tool use to sounds produced during nest building, i.e. culture, among wild orangutans. Much independent information is corroborating this interpretation. Here, after discussing the possible sources of error in this geographic approach, the chapter updates the estimate of the orangutan’s cultural repertoire by presenting the most recent table of locally varying (i.e. non-universal) orangutan behaviors found after exhaustive comparisons of records from eight sites with long-term orangutan field studies. There now is a minimum of between 26 and 35 of such cultural variants, depending on how one assesses the risk that some of them may in fact be hidden universals, missed by some observers or performed too rarely to be reliably recorded. There was little evidence for the alternative models explaining the geographic variation as an outcome of broad reaction norms toward variable ecology or demography, or of genetic differences between populations, both indicating an absence of social learning.

Orangutan populations are particularly susceptible to local extinction due to hunting, habitat loss, and fragmentation because they live at low population densities, grow slowly, and reproduce rarely. This chapter uses Population Viability Analysis (PVA) to consider the conservation implications of orangutan life history and population biology. First, a baseline model that incorporates the best available orangutan life-history data is presented. This model is then used to examine how plausible variation in model parameters, changes in the intensity of human-induced threats, and different conservation and management interventions would affect the probability of orangutan population persistence. The effects of existing threats on the extinction risk of specific orangutan populations on Borneo and Sumatra are also modelled. Finally, the conservation and management implications of this modeling exercise are considered.

African apes and orangutans experience temporal and spatial fluctuations in fruit availability with similar behavioral consequences. Relying on the African apes as a comparative ecogeographic model, this chapter examines jaw form among Pongo pygmaeus morio, P.p. wurmbii, and P. abelii to determine if these populations differ predictably in ways that reflect their ecological profiles. Pongo p. morio is characterized by the longest lean fruiting periods and relies to the greatest extent on resistant and hard foods. These orangutans are found to exhibit the relatively most robust mandible, and thus display the relatively greatest capacity to counter large and repetitive jaw loads. Pongo abelii, which maintains a fruit-dominated diet even in times of fruit scarcity, displays the relatively least robust mandible. Orangutans are further shown to display a relationship between variance in energy intake, feeding efficacy, and relative brain size, suggesting a link among morphological divergence, behavioral ecology, and life history.

Successful foraging, reproductive, and predator avoidance strategies in orangutans rely on their ability to navigate the complex three-dimensional habitat of tropical rainforest canopy. This chapter assimilates a broad collection of published studies, complemented by unpublished results to present a comprehensive interspecific comparison of the locomotion and postures employed by wild orangutans and the supports they use to travel and feed in the canopy. Despite methodological differences between studies, results imply that, while P. abelii and P. p. morio have the capacity to perform the same gross range of positional behaviors, they actually exhibit quantitatively different positional behavior repertoires and show distinct patterns of association between positional behavior and support use. However further research is necessary to establish whether the largest differences in positional behavior exist at the species- or habitat-level.

It has long been assumed that Sumatran forests are of higher quality for orangutans than Bornean forests, and that this is both the proximate and ultimate cause of many of the differences in socio-ecology between the two orangutan species. Yet this hypothesis has remained untested. This chapter presents data on the phenology and floristics of eight Bornean and three Sumatran forest sites where orangutans have been studied to examine the effects of floristic composition, habitat productivity, and seasonality on orangutan population density. The alternative hypotheses that higher orangutan densities in Sumatra are due to overall higher levels of plant productivity, the increased availability of preferred foods, the presence of more fallback foods, or differences in floristic composition between the two islands are tested empirically.

The chapter examines differences in the activity budgets of wild orangutans (Pongo spp.) within and between a large number of study sites in Sumatra and Borneo. The authors of the chapter found that each orangutan population appeared to follow one of two distinct foraging strategies: either (1) ‘sit and wait’, in which orangutans aim to minimize their energy expenditure by spending long periods of time resting and relatively short periods feeding and travelling; or (2) ‘search and find’ in which orangutans aim to maximize their energy intake by resting little and mainly feeding or moving in search of food. Orangutans adopt the first strategy in mixed-dipterocarp forests characterized by mast-fruiting events and irregular fruit availability; and adopt the second strategy in swamp forests with a regular supply of fruit, or in dryland forests with high strangling-fig density. The chapter proposes that the determining factor for which strategy is adopted is the temporal availability of fruit in the habitat, as opposed to other possibilities such as orangutan taxonomy.

This chapter explores variation in orangutan diets across their range, based on food lists. The authors of the chapter consolidated orangutan food lists from all available long-term field sites (N = 15). They represent both islands, multiple habitat types, varied degrees of degradation, and wild and rehabilitant populations. The chapter assesses the effects of habitat productivity (island, habitat type, habitat degradation) and rehabilitant–wild status on food lists. Findings suggest inverse relationships between habitat productivity and total plant taxa eaten at a site, the intensity at which individual food taxa are used, and the proportion of plant food species from which important food types are eaten. Analyses also explore food lists to suggest medical plant use, cultural influences on food knowledge, and the relationship between orangutan and other great ape diets. Discussion concerns conceptual implications of findings, methodological limitations to using food lists in the study of diet, and conservation applications.

Three groups of socially and cognitively complex nonhuman animals are discussed: elephants, cetaceans (whales and dolphins), and nonhuman great apes (gorillas, orangutans, bonobos, and chimpanzees). These are assessed in terms of a constellation of general characteristics that lead to rich social relationships among complex individuals, which in turn leads to ethical importance or considerability. The limits of epistemology and sociology of knowledge regarding factual realities are analyzed. The central place of language in ethical debates is assessed.

This chapter addresses some difficult theoretical issues which, up to this point, have been gingerly sidestepped. First, it offers an account of how chimpanzees interpret the interactions between the objects they use as tools and the effects that these objects produce. It illustrates the nature of this understanding by detailing one example of what is considered a ‘principle’ of the chimpanzees' folk physics. Second, it compares and contrasts a general theoretical stance with those of several previous theorists. Third, it outlines a number of potential objections to researcher'conclusions, and assesses each one in turn. The chapter concludes by offering a theory which may help to explain why chimpanzees and orangutans seem to make and use tools more than other nonhuman primates.

This chapter asserts that the fictional orangutans discussed in Chapter 5 offer commentary on Western society, either by directly addressing a human audience or by behaving in ways that highlight human shortcomings. Most of these apes have been removed from their original environment, and even Pierre Boulle's advanced apes live in a world that is functionally similar to the human world of the twentieth century rather than the jungle world of their ancestors. Other orangutans in fictional works either remain in their original habitats or bring their jungle wildness into contact with human society, often with catastrophic consequences for both. These orangutans are presented as clever creatures, but for the most part not as near-humans.

Social cognition covers a wide range of abilities such as empathy, joint attention, intentions, the understanding of beliefs and other mental states, cooperation, moral judgements, and the capacity for altruism. Hermann et al compared chimpanzees and orang-utans with children of two-and-a-half years old on six aspects of social cognition — space, quantities, causality, social learning, communication, and theory of mind — and found that the children surpassed the chimpanzees and orang-utans on five out of the six tests that they were presented with. This chapter discuses the specialized ability of the human brain to perform social cognition functions and explores several explanations for the limited ability of apes to carry out social cognition functions despite having the same ancestry and sharing certain physical attributes.

This chapter discusses the need to describe and measure the intelligence of various animals in order to use the comparative method to reconstruct cognitive evolution in humans. Especially, information on the relative intelligence of strepsirhines, New and Old World monkeys, gibbons, orangutans, gorillas, and the two species of chimpanzees is needed to cover the succession of early ancestors of humans that must have existed. It sounds straightforward, put like that, but it is not.