Orangutan Research Articles

Variation in Milk Proteins Across Lactation in Pongo pygmaeus and Gorilla gorilla.

Milk is a critical nutrition source for all neonatal mammals. In addition to nutrition, milk contains a multitude of bioactive molecules that likely affect neonatal physiology, metabolism, and immune function. We suggest that changes in the milk proteome across lactation reflect the changing need of the neonate and juvenile offspring. We used mass spectrometry to characterize the milk proteomes from a Pongo pygmaeus (12 samples) and a Gorilla gorilla (6 samples) housed at the Smithsonian's National Zoo and Conservation Biology Institute and trained to give milk samples. We found a total of 454 proteins from P. pygmaeus and 428 proteins from G. gorilla. We specifically characterized changes across lactation in 13 proteins representing multiple compartments of milk, including the milk fat globule membrane and whey. Additionally, we characterized changes in various immunoglobulin types, finding similarities to previously published studies on primate milks. Despite broad similarities between the milk proteomes of these two apes, we demonstrated that proteomes from samples from 8 to 12 months clustered by species/individual and were distinct. Samples from more individuals are required to distinguish whether our result demonstrates species differences or individual differences. This study represents a baseline study that other zoo-based milk studies can build from. All RAW data, MetaMorpheus search results, and PAW_BLAST results are available on MassIVE at ftp://massive.ucsd.edu/MSV000089723/.

Application of a parallel laser apparatus to measure forearms and flanges of wild Bornean orangutans (Pongo pygmaeus wurmbii).

We constructed a parallel laser photogrammetry apparatus constructed from commercially available parts, and measured forearm lengths and flange widths of 16 wild Bornean orangutans. Our objectives were to validate our method and apparatus, discuss issues encountered, and construct preliminary growth curves. For adult males, we also compared flange width to forearm length as a way to investigate the relationship between body size and flange development. We used a camera cage around a DSLR camera, on top of which we attached two parallel green lasers. We estimated error with repeatability, accuracy, and interobserver reliability measures, and measured forearm lengths in three different ways to see which was most consistent. The longest forearm measure was the most repeatable (CV = 1.64%), and was similar to flange repeatability (3.50%). Accuracy measurements of a known object were high (error = 0.25%), and Interobserver discrepancy low (3.74%). Laser spacing increased with distance to the subject, but we corrected for this using calibration photos after each session. We transparently discuss the issues we encountered with the aim that this accessible method can help expand the use of laser photogrammetry. Preliminary measurements show that male flange widths and forearm length do not reliably increase in tandem, and that female growth plateaus at around the age at first birth (15 years old). We conclude with suggested improvements to the apparatus and method to ensure the lasers remain parallel.

Restoring the orangutan in a Whole- or Half-Earth context

AbstractVarious global-scale proposals exist to reduce the loss of biological diversity. These include the Half-Earth and Whole-Earth visions that respectively seek to set aside half the planet for wildlife conservation or to diversify conservation practices fundamentally and change the economic systems that determine environmental harm. Here we assess these visions in the specific context of Bornean orangutansPongo pygmaeusand their conservation. Using an expert-led process we explored three scenarios over a 10-year time frame: continuation of Current Conditions, a Half-Earth approach and a Whole-Earth approach. In addition, we examined a 100-year population recovery scenario assuming 0% offtake of Bornean orangutans. Current Conditions were predicted to result in a population c. 73% of its current size by 2032. Half-Earth was judged comparatively easy to achieve and predicted to result in an orangutan population of c. 87% of its current size by 2032. Whole-Earth was anticipated to lead to greater forest loss and ape killing, resulting in a prediction of c. 44% of the current orangutan population for 2032. Finally, under the recovery scenario, populations could be c. 148% of their current size by 2122. Although we acknowledge uncertainties in all of these predictions, we conclude that the Half-Earth and Whole-Earth visions operate along different timelines, with the implementation of Whole-Earth requiring too much time to benefit orangutans. None of the theorized proposals provided a complete solution, so drawing elements from each will be required. We provide recommendations for equitable outcomes.

Literature Analysis on the Bornean Orangutan (Pongo Pygmaeus) Conservation Ecotourism in Tanjung Puting National Park, Waringin Barat City, Central Kalimantan

Purpose: The purpose of the study is to analyze the development of orangutans conservation ecotourism in Tanjung Puting National Park based on previous studies.
 Research Methods: The methodology used in this study is a literature review approach. Data collection was carried out by collecting data and information in the form of related journals from previous research.
 Results and Discussion: Synchronization and collaboration between stakeholders is important in improving the management of TPNP and implementing policies so that they are effective and optimal
 Implication: The dynamics of orangutan conservation are not being implemented according to their natural habitat.
 
 Keywords: ecotourism, conservation, Bornean orangutan (pongo pygmaeus).

Host species and habitats shape the bacterial community of gut microbiota of three non-human primates: Siamangs, white-handed gibbons, and Bornean orangutans.

The gut microbiome is essential for a host to digest food, maintain health, and adapt to environments. Bacterial communities of gut microbiota are influenced by diverse factors including host physiology and the environment. Many non-human primates (NHPs), which are physiologically close to humans, are in danger of extinction. In this study, the community structure of the gut microbiota in three NHPs: siamangs (Symphalangus syndactylus, Ss), Bornean orangutans (Pongo pygmaeus, Pp), and white-handed gibbons (Hylobates lar, Hl)—housed at the largest Zoo in Taiwan were analyzed. Pp and Ss were housed in the Asian tropical rainforest area, while Hl was housed in two separate areas, the Asian tropical rainforest area and the conservation area. Bacterial community diversity of Ss, indicated by the Shannon index, was significantly higher compared with that of Hl and Pp, while the richness (Chao 1) and observed operational taxonomic units (OTUs) were similar across the three species of NHPs. Host species was the dominant factor shaping the gut microbial community structure. Beta-diversity analysis including non-metric multidimensional scaling (NMDS) and unweighted pair group method with arithmetic mean (UPGMA) suggested gut bacterial communities of Hl housed in the conservation area were closely related to each other, while the bacterial communities of Hl in the rainforest area were dispersedly positioned. Further analysis revealed significantly higher abundances of Lactobacillus fermentum, L. murinus, and an unclassified species of Lactobacillus, and a lower abundance of Escherichia-Shigella in Hl from the conservation area relative to the rainforest area. The ratio of Lactobacillus to Escherichia-Shigella was 489.35 and 0.013 in Hl inhabiting the conservation and rainforest areas, respectively. High abundances of Lactobacillus and Bifidobacterium and a high ratio of Lactobacillus to Escherichia-Shigella were also observed in one siamang with notable longevity of 53 years. Data from the study reveal that host species acted as the fundamental driving factor in modulating the community structure of gut microbiota, but that habitats also acted as key determinants within species. The presence and high abundance of probiotics, such as Bifidobacterium and Lactobacillus, provide potential indicators for future diet and habitat optimization for NHPs, especially in zoological settings.

Stable isotopic investigation of the feeding ecology of wild Bornean orangutans

AbstractObjectivesWe applied stable carbon and nitrogen isotope analyses to wild Bornean orangutans (Pongo pygmaeus morio) to investigate the feeding ecology of wild orangutans. Compared with African great ape species, orangutans are adapted to environments with chronic lower nutrition. But the usefulness of stable isotope analysis in the study of wild orangutan feeding ecology has not been fully explored.MethodsThe study site was a primary lowland dipterocarp forest in the Danum Valley, Sabah, Malaysia. A total of 164 plant and 94 fecal samples collected across 18 months were analyzed.ResultsCarbon and nitrogen stable isotope ratios of plant food samples do not systematically vary by plant parts (i.e., bark, fruits, and leaves). Elemental composition and stable isotope ratios of orangutan feces do not systematically vary by orangutans' sex and age classes, although fecal stable isotope ratios showed seasonal fluctuations. No isotopic contribution of breast milk was found in fecal samples collected from individuals at 2.7–6.5 years of age.ConclusionsThis study revealed key characteristics of the stable isotope ecology of wild orangutans living in a primary lowland forest. Although there was little isotopic variation among plant foods and orangutan individuals, seasonal fluctuations in baseline isotope ratios or orangutans' diet were found in Danum valley.

Social tolerance and interactional opportunities as drivers of gestural redoings in orang-utans.

Communicative repair is a fundamental and universal element of interactive language use. It has been suggested that the persistence and elaboration after communicative breakdown in nonhuman primates constitute two evolutionary building blocks of this capacity, but the conditions favouring it are poorly understood. Because zoo-housed individuals of some species are more social and more terrestrial than in the wild, they should be more likely to show gestural redoings (i.e. both repetition and elaboration) after communicative failure in the coordination of their joint activities. Using a large comparative sample of wild and zoo-housed orang-utans of two different species, we could confirm this prediction for elaboration, the more flexible form of redoings. Specifically, results showed that gestural redoings in general were best predicted by the specific social action context (i.e. social play) and interaction dyad (i.e. beyond mother-offspring), although they were least frequent in captive Bornean orang-utans. For gestural elaboration, we found the expected differences between captive and wild research settings in Borneans, but not in Sumatrans (the more socially tolerant species). Moreover, we found that the effectiveness of elaboration in eliciting responses was higher in Sumatrans, especially the captive ones, whereas effectiveness of mere repetition was influenced by neither species nor setting. We conclude that the socio-ecological environment plays a central role in the emergence of communicative repair strategies in great apes. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Deforestation projections imply range-wide population decline for critically endangered Bornean orangutan

Assessing where wildlife populations are at risk from future habitat loss is particularly important for land-use planning and avoiding biodiversity declines. Combining projections of future deforestation with species density information provides an improved way to anticipate such declines. Using the critically endangered Bornean orangutan (Pongo pygmaeus) as a case study we applied a spatio-temporally explicit deforestation model to forest loss data from 2001 to 2017 and projected future impacts on orangutans to the 2030s. Our projections point to continued deforestation across the island, amounting to a potential loss of forest habitat for 26,200 orangutans. Populations currently persisting in forests gazetted for industrial timber and oil palm concessions, or unprotected forests outside of concessions, were projected to experience the worst losses within the next 15 years, amounting to 15,400 individuals. Our analysis indicates the importance of protecting orangutan habitat in plantation landscapes, maintaining protected areas and efforts to prevent the conversion of logged forests for the survival of highly vulnerable wildlife. The modeling framework could be expanded to other species with available density or occurrence data. Our findings highlight that species conservation should not only act on the current information, but also anticipate future changes to be effective.

Milk microbiomes of three great ape species vary among host species and over time

In mammalian neonates, milk consumption provides nutrients, growth factors, immune molecules, and microbes. Milk microbiomes are increasingly recognized for their roles in seeding infant gut microbiomes and priming immune development. However, milk microbiome variation within and among individuals remains under investigation. We used 16S rRNA gene sequencing to investigate factors shaping milk microbiomes in three captive great ape species: Gorilla gorilla gorilla (individuals, N = 4; samples, n = 29), Pongo abelii (N = 2; n = 16), and Pongo pygmaeus (N = 1; n = 9). We demonstrate variation among host species, over lactation, and between housing facilities. In phylogenetic community composition, milk microbiomes were distinct among the three ape species. We found only a few shared, abundant bacterial taxa and suggest that they likely serve functional roles. The diversity and community composition of milk microbiomes showed gradual changes over time in gorillas and the Bornean orangutan, which was detectable with our comprehensive sampling over lactation stages (> 300-day span). In gorillas, milk microbiomes differed between housing facilities, but were similar between dams within a facility. These results support the strong influence of evolutionary history in shaping milk microbiomes, but also indicate that more proximate cues from mother, offspring, and the environment affect the distribution of rarer microbial taxa.

Decolonizing Extinction

The now three species of orangutan populating the islands of Borneo and Sumatra represent some of the most threatened primates in the world, and growing global consumption of palm oil is only exacerbating the destruction and continual fragmentation of their habitats. In her book, “Decolonizing Extinction: The Work of Care in Orangutan Rehabilitation,” Dr. Juno Parreñas outlines a new approach to many common conservation concerns surrounding these Great Apes. Parreñas reimagines what it means to decolonize within the context of conservation and rapid extinction threat on both a population and genus level. With specific attention paid to the Bornean orangutans of Sarawak, Malaysia (Pongo pygmaeus pygmaeus), Parreñas argues for thinking outside the traditional aims of most current conservation initiatives, acknowledging the inherent limitations and shortcomings of these approaches, and for looking towards co-habitation and a shared vulnerability with the non-human other. Parreñas expertly crosses disciplinary boundaries by highlighting the complexity of relations and contexts that situate all conservation efforts: the underlying biases inherent to sexual inequality and privilege, which behaviours are considered normal or natural, and the limitations of empathy when wage labour is so depended upon it replaces traditional beliefs and taboos that had previously connected humans to non-human others, like orangutans, quite intimately. This review of her book provides a brief overview of the themes within “Decolonizing Extinction,” summarizing the main points of the chapter sections, and emphasizes the need for thinking outside the box when planning for conservation of the non-human other.

The curious case of great ape curiosity and how it is shaped by sociality

AbstractAlthough curiosity has huge implications for human creativity and learning, its evolutionary roots and function in animals remain poorly understood. Modern humans, who lack natural predators, thrive with curiosity, but our ancestors faced more hazardous environments that would not necessarily favor individual curiosity. Instead, being curious may have undergone selection in interaction with sociality. Our closest living relatives, the great apes (henceforth apes) have evolved facing conditions more like human ancestors and as such, can help us understand the functions of curiosity and its expression in non‐human species. In this study, we defined curiosity as a combination of behavioral traits like neophilia, exploration diversity, and prolonged interest in exploring novelty and compared it, under similar captive environments across four ape species (N = 101):Pan troglodytes,Pan paniscus,Pongo abelii,andPongo pygmaeus. Results revealed that curiosity followed a linear gradient across the four species in accordance with their sociality. We proposethe social curiosity hypothesisto explain the observed pattern, reflecting those individuals in highly social species, like bonobos and chimpanzees, regularly are accompanied by conspecifics, and thereby accustomed to an abundance of social cues, leading to inhibited curiosity when alone, compared to more solitary orangutans. As such, our study implies that ape curiosity evolved interlinked with sociality. Further, a subset of the sample (N = 46) enabled us to examine if curiosity benefits problem‐solving skills, but our data did not support such link.

Assessments made easier: examining the use of a rating-based questionnaire to capture behavioral data in rehabilitant orangutans (Pongo pygmaeus morio)

Rehabilitation and release are commonly used for confiscated, surrendered, and rescued primates. To improve release efficacy it is important to generate accurate behavioral profiles of release candidates. Research on primates traditionally uses observer ratings to measure individual differences. This method is easily implemented, but its validity has been questioned. We evaluated whether observer ratings reflect behavioral data indicating forest adaptation in 18 free-ranging rehabilitant orangutans (Pongo pygmaeus morio). In 2017, we used a species-specific questionnaire to measure how often orangutans engaged in behaviors linked to living successfully in the wild (e.g., nest building) and the extent to which they express personality traits that may influence forest adaptation. We collected 11 months of observational data on 17 of the orangutans concurrently to validate the questionnaire items, and collected further questionnaire data for 16 of the individuals in 2019. We used regularized exploratory factor analysis (REFA) and parallel analysis to condense the ratings and determine that two factors could be reliably extracted. We conducted another REFA using the observational data, and calculated factor congruence coefficients following procrustean rotation. The first of the two factors represented forest skills and human aversion, and was congruent with observational data. The second factor reflected boldness, sociability, and exploration, and was not congruent with observational data. Ratings correlated significantly with observations for all five questionnaire items reflecting adaptation to forest life, and for three of seven items reflecting personality traits. We conclude that ratings can be a valid approach to obtain individual-based behavioral information reflecting forest adaptation in free-ranging rehabilitant orangutans, and may be particularly useful in summarizing behaviors relevant to forest adaptation that are otherwise challenging to gather in primates.

Suitability for salt-lick tourism: A preliminary assessment on the natural salt-licks at Segaliud-Lokan Forest Reserve, Sandakan, Sabah

The natural salt-licks are visited by various species of terrestrial mammals, hence ideal for mammal watching, although the suitability for salt-lick tourism is influenced by other factors. Preliminary research was conducted on the suitability of four natural salt-licks for mammal watching in Segaliud-Lokan Forest Reserve (SLFR), Sabah. The camera trapping survey and field assessment were conducted for eight months, and then the assessment criteria applied in this study included the lick accessibility, detection frequency, species richness, viewable activity sighting probability, reliability and visibility on the terrestrial mammals, at a given lick. A total of 12 different mammal species were recorded, where Sambar Deer, Bearded Pig, Banteng, and Bornean Orang-utan were determined as the main visitor species of this study. Among the four selected salt-licks, the rating score of SL50A (Score=1.71) was significantly lower than those of SL50B, SL56 and SL59 (Score=2.57 respectively, χ2 2 =6.794, p=0.042), hence highlighting that SL50A was not suitable for conducting mammal watching activity, unlike the other three natural licks at SLFR. The assessment on the compatibility between the supply (mammalian physical availability) and demand (highly anticipated species) was excluded from this research, therefore emphasizing the need to fill up this particular research gap in the future.

Preliminary findings of age and male sexual characteristics andand potential effect to semen characteristics and cryopreservation of the critically endangered Bornean orangutan in Malaysia

Bornean orangutan is a critically endangered non-human primate; however, the threat of extinction is not merely from poaching and habitat loss. Orangutan survival is also threatened by the genetic loss and genetic bottleneck due to the low effective population, prompting the dire need for an immediate genetic preservation program through systematic biobanking and assisted reproductive technology (ART). This study aims to provide integral data to the semen characteristics, extension, and cryopreservation of the Bornean orangutan and the potential relationship to male traits. Five captive orangutans from Sepilok Orangutan Rehabilitation Centre (SORC) with a mean body weight of 52.81 ± 7.00kg were used for this study. Semen collection was performed using electroejaculation (EE) under complete general anesthesia. Semen was subjected to macroscopic and microscopic evaluation while testicular measurement was obtained using digital calipers. The semen characteristics of the orangutans are volume (778 ± 250.21µl), pH (7.80 ± 0.25), concentration (32.38 ± 17.40 × 106 sperm/ml), total motility (61.00 ± 12.88%), adjusted motility index (48.76 ± 11.32%), live spermatozoa (77.75 ± 6.94%) and normal spermatozoa (11.48 ± 11.34%). Analysis of variance statistical analysis test was used to compare the significant difference between means, at (p < 0.05). Spermatozoa concentration was the only significant different parameter between individuals. Testes biometry parameters are statistically significant between the flanged and unflanged individuals. Live spermatozoa are different in adult and sub-adult individual while teratospermia was found to be consistently high in all individuals. Chilled and post-thaw quality after cryopreservation suggests promising survivability of spermatozoa. Semen collection with EE yields a consistent and acceptable quality of spermatozoa for cryopreservation, biobanking purposes, and potential application of ART.

“Engaging the Enemy”: Orangutan (Pongo pygmaeus morio) Conservation in Human Modified Environments in the Kinabatangan floodplain of Sabah, Malaysian Borneo

Throughout the equatorial tropics, forest conversion to agriculture often fragments crucial primate habitat. In 30 years, 80% of the alluvial lowland forests along the Kinabatangan River in Sabah, Malaysian Borneo, have been supplanted by oil palm (Elaeis guineensis) plantations. Today, only about 20% of the former orangutan (Pongo pygmaeus morio) population remains in the region. Because most of the land is now under the tenure of agribusiness companies, we used a pragmatic approach of mixed biosocial methods and citizen science engagement of oil palm growers (N = 6) as active conservation partners to study orangutan use of the privately administered landscape between protected forest fragments. We found that 22 of 25 remanent forest patches (0.5 to 242 hectares) surveyed within plantations contained food or shelter resources useful for orangutans. Of these, 20 are in regular transitory use by wider-ranging adult male orangutans, and in 9 patches, females are resident and raising offspring isolated within oil palm plantations. These findings indicate that orangutans retain a measure of normal metapopulation dynamics necessary for viability at the landscape level despite drastic habitat modification. We found that barriers to in situ conservation in these agroforest matrices were due to the following misconceptions across sectors: 1) Good farming practices require exclusion of wildlife; 2) Orangutans seen in plantations must be “rescued” by people; and 3) Translocation is an appropriate conservation strategy, and nondetrimental to orangutans. Our exploratory study exemplifies the value of biosocial methods and collaboration with industrial-scale farmers to support primate resilience in forests fragmented by agriculture.

Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the positions of the nasal tips of Plio-Pleistocene hominids.

By identifying homogeneity in bone and soft tissue covariation patterns in living hominids, it is possible to produce facial approximation methods with interspecies compatibility. These methods may be useful for producing facial approximations of fossil hominids that are more realistic than currently possible. In this study, we conducted an interspecific comparison of the nasomaxillary region in chimpanzees and modern humans with the aim of producing a method for predicting the positions of the nasal tips of Plio-Pleistocene hominids. We addressed this aim by first collecting and performing regression analyses of linear and angular measurements of nasal cavity length and inclination in modern humans (Homo sapiens; n = 72) and chimpanzees (Pan troglodytes; n = 19), and then performing a set of out-of-group tests. The first test was performed on four subjects that belonged to the same genus as the training sample, i.e., Homo (n = 2) and Pan (n = 2), and the second test, which functioned as an interspecies compatibility test, was performed on Pan paniscus (n = 1), Gorilla gorilla (n = 3), Pongo pygmaeus (n = 1), Pongo abelli (n = 1), Symphalangus syndactylus (n = 3), and Papio hamadryas (n = 3). We identified statistically significant correlations in both humans and chimpanzees with slopes that displayed homogeneity of covariation. Prediction formulae combining these data were found to be compatible with humans and chimpanzees as well as all other African great apes, i.e., bonobos and gorillas. The main conclusion that can be drawn from this study is that our set of regression models for approximating the position of the nasal tip are homogenous among humans and African apes, and can thus be reasonably extended to ancestors leading to these clades.

Designing an Android-Based Borneo Orangutan Adventure Game Using Scirra Construct 2

Currently the game is very popular with many people. Because the game is a game that uses a smartphone that is easy to carry everywhere, the game is also a form of multimedia entertainment that is made as attractive as possible. Even game makers make it as interesting and fun as possible so that the general public can use it. In this study, the Borneo orangutan adventure game aims to introduce orangutans in Central Kalimantan and the life of orangutans. The benefits of this research are for entertainment media and the introduction of Bornean orangutans. This game is designed with multimedia software method. From the results of the black box test the application is in accordance with the purpose of making the game while the results of the questionnaire respondents with a Likert scale show that 91.2% are on a very good scale or satisfied in terms of the appearance of the game and the way the game operates.

CardiOvascular examination in awake Orangutans (Pongo pygmaeus pygmaeus): Low-stress Echocardiography including Speckle Tracking imaging (the COOLEST method).

IntroductionCardiovascular diseases have been identified as a major cause of mortality and morbidity in Borneo orangutans (Pongo pygmaeus pygmaeus). Transthoracic echocardiography is usually performed under anesthesia in great apes, which may be stressful and increase risks of peri-anesthetic complications in case of cardiac alteration. The aim of the present pilot study was hence to develop a quick and non-stressful echocardiographic method (i.e., the COOLEST method) in awake Borneo orangutans (CardiOvascular examination in awake Orangutans: Low-stress Echocardiography including Speckle Tracking imaging) and assess the variability of corresponding variables.Materials and methodsFour adult Borneo orangutans trained to present their chest to the trainers were involved. A total of 96 TTE examinations were performed on 4 different days by a trained observer examining each orangutan 6 times per day. Each examination included four two-dimensional views, with offline assessment of 28 variables (i.e., two-dimensional (n = 12), M-mode and anatomic M-mode (n = 6), Doppler (n = 7), and speckle tracking imaging (n = 3)), representing a total of 2,688 measurements. A general linear model was used to determine the within-day and between-day coefficients of variation.ResultsMean±SD (minimum-maximum) images acquisition duration was 3.8±1.6 minutes (1.3–6.3). All within-day and between-day coefficients of variation but one (n = 55/56, 98%) were <15%, and most (51/56, 91%) were <10% including those of speckle tracking systolic strain variables (2.7% to 5.4%).DiscussionHeart morphology as well as global and regional myocardial function can be assessed in awake orangutans with good to excellent repeatability and reproducibility.ConclusionsThis non-stressful method may be used for longitudinal cardiac follow-up in awake orangutans.

Pongo pygmaeus (orang-utan)

This datasheet on Pongo pygmaeus covers Identity, Distribution.

Orangutan (Pongo pygmaeus wurmbii) human-oriented behavior at the Lamandau Wildlife Reserve, Indonesia

Abstract. Amalia N, Fajarallah DP, Atmoko SSU. 2021. Orangutan (Pongo pygmaeus wurmbii) human-oriented behavior at the Lamandau Wildlife Reserve, Indonesia. Biodiversitas 23: 396-402. Unlike other conservation efforts, rehabilitation and reintroduction face different challenges due to humans' role in developing orphaned orangutans. Long-term interactions between orangutans and humans in captivity will gradually encourage orangutans to shape and increase human-oriented behavior (interest in humans). The Lamandau Wildlife Reserve (Lamandau WR) applies the soft-release method for the orangutan release process. Additional feed is provided every day. The correlation between animal-human interactions as part of the conservation efforts evaluation is essential to study. This study aimed to analyze the human-oriented behavior of the orangutan population in the Lamandau WR based on the observation sites (camp, feeding site, and forest) and the age-sex class of orangutans. This study also identified the factors that affected them. The study was conducted for five months (July-November 2019). During the observation, the factor of current age was suspected to affect human-oriented behavior. Human-oriented behavior is divided into three categories based on the orangutans' response: approaching, avoidance, and no response. The highest rates of human-oriented behavior in orangutans were approaching category. The highest promoting behavior was noticed at the camp and feeding site, especially young orangutans and mothers. Interest in humans can be explained by the 'captive effect' phenomenon where captive orangutans are more likely to independently explore the novelty (unfamiliar objects/foods) than their wild counterparts.