Orangutan Research Articles

Detecting the presence of different Retzius periodicities at the population level from repetitive linear enamel hypoplasia among Lufengpithecus lufengensis and Pongo pygmaeus.

Reconstruction of life histories for fossil and living primates draws on rate of enamel layering, termed Retzius periodicity (RP in days) expressed as surface perikymata, during dental crown formation. Disclosure of RP through thin sectioning is destructive; consequently, sample sizes are inadequate to detect the range of RPs present in discrete taxa. We propose an additional method to detect RPs at the population level based on twice-yearly average recurrence of linear enamel hypoplasia (rLEH) in apes shown by prior studies. Casts of teeth from orangutans (Pongo pygmaeus) (n = 40) and Lufengpithecus lufengensis (n = 57) from Late Miocene Shihuiba, China, (133 and 138 LEH, respectively) were recorded with scanning electron microscope (SEM) and confocal microscopy to yield perikymata counts between episodes of LEH. Frequency distributions of aggregated perikymata counts between LEH were compared to frequency distribution of tooth-specific ratios of perikymata counts between successive LEH (this latter step removes effects of RP differences within a sample). Drawing on prior research, two successive intervals between LEH span 1 year on average. Ratios of successive to previous intervals between LEH show that orangutans and Lufengpithecus exhibit two asymmetric intervals centered on 5.3 and 6.7 months, likely reflecting the effect of axial tilt insolation on phenology. Estimated RPs are not unimodal but show a range from 7 to 12 in Lufenpithecus and 8 to 11 in Pongo, comparable to published values. Repetitive LEH is sufficiently regular to detect additional RPs which, in the case of Lufengpithecus, have yet to be demonstrated histologically.

Complete sequencing of ape genomes.

We present haplotype-resolved reference genomes and comparative analyses of six ape species, namely: chimpanzee, bonobo, gorilla, Bornean orangutan, Sumatran orangutan, and siamang. We achieve chromosome-level contiguity with unparalleled sequence accuracy (<1 error in 500,000 base pairs), completely sequencing 215 gapless chromosomes telomere-to-telomere. We resolve challenging regions, such as the major histocompatibility complex and immunoglobulin loci, providing more in-depth evolutionary insights. Comparative analyses, including human, allow us to investigate the evolution and diversity of regions previously uncharacterized or incompletely studied without bias from mapping to the human reference. This includes newly minted gene families within lineage-specific segmental duplications, centromeric DNA, acrocentric chromosomes, and subterminal heterochromatin. This resource should serve as a definitive baseline for all future evolutionary studies of humans and our closest living ape relatives.

Gastrointestinal parasites of wild Bornean orang-utans (Pongo pygmaeus) in a habitat affected by wildfire smoke

Wildfires are becoming increasingly frequent and severe in the tropical peatlands of Southern Borneo, with major consequences for both wildlife and people that inhabit them. Burning peat releases vast amounts of toxic smoke that, when inhaled, can cause a plethora of health-related issues. With some of the largest remaining populations of Bornean orang-utans (Pongo pygmaeus) being found in peatland forests, wildfires are becoming one of the greatest threats to this Critically Endangered ape, yet the effects of the toxic smoke on their health are unknown. Wildfire has long been known to influence wildlife disease by reducing populations of free-living parasites in the environment (thus altering host exposure), and there is a growing body of evidence to suggest that smoke may affect host susceptibility to such parasites by diminishing physiological condition and immune function. In this study, we investigated parasitic nematode infections in wild Bornean orang-utans inhabiting a drained peatland forest prone to fire and smoke. We identified four gastrointestinal nematode taxa that varied significantly in their prevalence and intensity. Overall prevalence of nematode infection was high, but intensity was relatively low. We present some evidence for an increase the prevalence and intensity of certain nematode taxa after the wildfire smoke event. Namely, an increase in the prevalence of Enterobius spp. and Trichuris spp., and an increase in the intensity of hookworm infections, after the smoke period. We identify the need for multi-year, multi-fire event research to increase sample sizes, along with measuring endocrinological markers of physiological condition, in tandem with parasitological monitoring, to gain a more comprehensive understanding of the impacts of environmental changes on orang-utan health.

Pongo's ecological diversity from dental macrowear analysis

AbstractObjectivesOrangutans are found in tropical rainforests of Borneo (Pongo pygmaeus) and Sumatra (Pongo abelii and Pongo tapanuliensis), and they are primarily considered frugivorous species. However, ecological studies reported differences in feeding behavior between these species. P. pygmaeus spend more time feeding on low‐quality foods, such as bark and tough vegetation than do P. abelii. The aim of this study is to investigate if there is any geographic variation in molar macrowear pattern between the two species.MethodsWe analyzed the macrowear pattern of second mandibular molars of 58 orangutan specimens combining dental topographic measurements (occlusal relief index, percentage of dentine exposure, and percentage of enamel wear) with the occlusal fingerprint analysis method.ResultsThe molar macrowear patterns of P. abelii and P. pygmaeus show no significant differences in most of the variables examined in this study. While P. pygmaeus molars are generally characterized by flatter occlusal morphology with slightly larger crushing and grinding areas than those of P. abelii, these differences are not statistically significant. However, we do observe a more variable wear in P. pygmaeus.ConclusionsSimilarities in molar macrowear patterns between the two species could be linked to overlapping long‐term diets, primarily composed of ripe and pulpy fruits. Dental macrowear is a cumulative process that occurs during the individual's lifetime, and it may be difficult to detect seasonal changes through its examination. Future studies could integrate tooth micro‐ and macrowear data for a better understanding of primate dental ecology.

Phylo-Epigenetics in Phylogeny Analyses and Evolution.

Long-standing, continuous blurring and controversies in the field of phylogenetic interspecies relations, associated with insufficient explanations for dynamics and variability of speeds of evolution in mammals, hint at a crucial missing link. It has been suggested that transgenerational epigenetic inheritance and the concealed mechanisms behind play a distinct role in mammalian evolution. Here, a comprehensive sequence alignment approach in hominid species, i.e., Homo sapiens, Homo neanderthalensis, Denisovan human, Pan troglodytes, Pan paniscus, Gorilla gorilla, and Pongo pygmaeus, comprising conserved CpG islands of housekeeping genes, uncover evidence for a distinct variability of CpG dinucleotides. Applying solely these evolutionary consistent and inconsistent CpG sites in a classic phylogenetic analysis, calibrated by the divergence time point of the common chimpanzee (P. troglodytes) and the bonobo or pygmy chimpanzee (P. paniscus), a "phylo-epigenetic" tree has been generated, which precisely recapitulates branch points and branch lengths, i.e., divergence events and relations, as they have been broadly suggested in the current literature, based on comprehensive molecular phylogenomics and fossil records of many decades. It is suggested here that CpG dinucleotide changes at CpG islands are of superior importance for evolutionary developments. These changes are successfully inherited through the germ line, determining emerging methylation profiles, and they are a central component of transgenerational epigenetic inheritance. It is hidden in the DNA, what will happen on it later.

Comparing cranial suture interdigitation in humans and non-human primates: unearthing links to osteopathic cranial concept.

Since William Garner Sutherland's inception of osteopathic cranial manipulative medicine (OCMM), osteopathic physicians have practiced with the knowledge that cranial sutures exhibit motion. We hypothesize that the complexity of suture interdigitation in humans may provide clues to elucidate the concept of OCMM. We compared the interdigitation of sagittal, coronal (left and right), and lambdoid (left and right) sutures in computed tomography (CT) scans of humans and five nonhuman primate species (Gorilla gorilla, Pongo pygmaeus, Pan troglodytes, Hylobates lar, and Nasalis larvatus). Human ages are evenly distributed between 10 and 65 years of age, with an equal number of males (n=16) and females (n=16) in the sample. Nonhuman primates are all females, and the sample includes juveniles (n=6) and adults (n=34). Sutures were evaluated on a scale ranging from 0 to 3 (0: fused sutures; 1: no interdigitation; 2: low complexity; and 3: representing the highest degree of interdigitation and complexity). Based on ordinary least squares linear regression, we found no significant relationship between suture interdigitation and age in humans. Chi-square tests were utilized to assess sex differences within humans, species-level differences, and differences between humans and nonhuman primates across all five sutures. Humans exhibited a statistically significant greater degree of suture complexity than all five nonhuman species across all five sutures. These findings indicate that human suture interdigitation is more complex than their closest living relatives (African apes) and other primates (Asian monkeys and apes). We theorize that this would enable subtle movement and serve to transmit forces at the cranial sutures from dietary or ethological behaviors, similar to the pattern observed in other mammals. While humans have a softer diet compared to other living primates, the uniqueness of human craniofacial growth and extended developmental period could contribute to the necessity for complex cranial sutures. More studies are needed to understand variation in human and nonhuman sutural complexity and its relationship to cranial motion.

CLINICAL MANAGEMENT OF CHRONIC ORANGUTAN RESPIRATORY DISEASE SYNDROME IN THREE ADULT MALE BORNEAN ORANGUTANS (PONGO PYGMAEUS).

Orangutan respiratory disease syndrome (ORDS) is a disease unique to orangutans (Pongo sp), characterized by chronic bacterial infection and inflammation of any region or combination of regions of the respiratory tract, including the sinuses, air sacs, cranial bones, airways, and lung parenchyma. Aggressive early intervention during a first episode may prevent progression to chronic disease. However, in the setting of an established chronic disease, intermittent acute exacerbations are associated with worsening symptoms and increased infection and inflammation. ORDS is ultimately fatal due to loss of respiratory function resulting from chronic structural damage. Utilizing potentially lifelong medications to slow the progression of chronic, destructive inflammation in the respiratory tract, chronic treatment is aimed at stabilizing the animals' respiratory function, decreasing the frequency of recurrent exacerbations, and improving their general well-being. Three adult male Bornean orangutans (Pongo pygmaeus) housed at an orangutan rehabilitation and reintroduction center in Indonesia have long histories of recurrent respiratory disease. Each underwent CT scans confirming ORDS with chronic airway disease prior to initiation of a long-term treatment protocol. Based on data-driven medical management of bronchiectasis in humans, the three orangutans have been treated with long-term combination regimens of oral azithromycin, nebulized salbutamol, and nebulized hypertonic saline. Follow-up CT scans in all three animals at least 1 yr following treatment initiation showed improvements throughout their respiratory tracts. The duration of each exacerbation period decreased, and the orangutans have longer symptom-free periods compared to before the start of treatment. At an average of 5 yr into the long-term treatment protocol, all three orangutans are thriving. Chronic medical management of ORDS modeled after human treatment of bronchiectasis has been efficacious in these three orangutans and encourages further study of this approach.

Bornean Orangutan Nest Classification using Image Enhancement with Convolutional Neural Network and Kernel Multi Support Vector Machine Classifier

Preserving wildlife habitats is crucial in mitigating climate change. Species like orangutans and monkeys contribute to fruiting and planting in forests. The World Wide Fund Sabah Malaysia faces challenges in manually identifying and classifying orangutan nests for studying their behaviour and conserving their habitats. To address this, we propose automating the classification of captured images using machine learning algorithms. This research involves three key components: image processing, feature extraction, and image classification. Our proposed image processing includes several steps, such as image pre-processing and enhancement techniques like local contrast enhancement, sharpening, intensity adjustment, histogram equalization, and colour thresholding. We applied four different Convolutional Neural Networks (CNNs) to extract and identify orangutan nests’ features. Subsequently, we utilize Support Vector Machine (SVM) for image classification. The results reveal that the Inception Residual Network Version 2 (ResNet-v2) achieves the best performance. This architecture is then combined with a kernel SVM to classify Bornean orangutan nests. Our approach demonstrates impressive results, boasting an accuracy of 96.60%, an F1-score of 96.60%, a precision of 96.59%, and a recall of 96.58%. These metrics underscore the high accuracy and effectiveness of our proposed methodology for classifying Bornean orangutan nests. By reducing the need for extensive human intervention in image analysis, our method presents a valuable tool for conservationists and researchers committed to studying and safeguarding these endangered orangutans and their habitats. In future work, we aim to develop orangutan nest detector, contributing to wildlife conservation research.

Identification of Orangutan Nest Tree Types (Pongo pygmaeus) in KHDTK Mungku Baru, Palangka Raya, Central Kalimantan

Muhammadiyah University of Palangkaraya has a KHDTK covering an area of ​​4,910 ha. However, research on Orangutan is still very minimal and limited to KHDTK Mungku Baru. Therefore, this research aims to determine several trees used for habitat and food for orangutans (Pongo pygmaeus) in KHDTK Mungku Baru, Palangka Raya City, Central Kalimantan. Observations from research on Orangutan (P. pygmaeus) nests showed that there were 19 nests from 27 tree species identified in 9 different tree species, dominated by Meranti (Shorea) and Guava (Syszgium) trees. Characteristics of Orangutan (P. pygmaeus) nests: There are 5 types of nests, namely types A, B, C, D and E.

Identification and antibiotic resistance patterns of Klebsiella sp. isolated from the feces of Bornean Orangutans (Pongo pygmaeus) at Taman Safari Indonesia, Bogor

Orangutans are the only great apes that still survive in the Southeast Asian Region. However, their population in the wild habitat continues to decline, with estimates indicating a 50% decreased over the last 60 years. There is limited microbiological data on the antibiotic resistance of Klebsiella sp. in the feces of Bornean Orangutan (Pongo pygmaeus). This study aimed to identify the presence of Klebsiella sp. and assess its resistance pattern to various antibiotics in the feces of Bornean Orangutans. The research involved isolation, identification, and antibiotic resistance testing. Results showed that three isolates (37.5%) were positive for Klebsiella sp. Sensitivity test revealed two distinct resistance patterns among Klebsiella sp. isolates from the feces of healthy P. pygmaeus in Taman Safari Indonesia, Bogor. These isolates exhibited resistance to β-lactam antibiotics but remained sensitive to aminoglycoside, tetracycline, and fluoroquinolone antibiotics.

Application of Machine Learning for Automating Behavioral Tracking of Captive Bornean Orangutans (Pongo Pygmaeus).

This article applies object detection to CCTV video material to investigate the potential of using machine learning to automate behavior tracking. This study includes video tapings of two captive Bornean orangutans and their behavior. From a 2 min training video containing the selected behaviors, 334 images were extracted and labeled using Rectlabel. The labeled training material was used to construct an object detection model using Create ML. The use of object detection was shown to have potential for automating tracking, especially of locomotion, whilst filtering out false positives. Potential improvements regarding this tool are addressed, and future implementation should take these into consideration. These improvements include using adequately diverse training material and limiting iterations to avoid overfitting the model.

Phylogenetic differences in the morphology and shape of the central sulcus in great apes and humans: implications for the evolution of motor functions.

The central sulcus divides the primary motor and somatosensory cortices in many anthropoid primate brains. Differences exist in the surface area and depth of the central sulcus along the dorso-ventral plane in great apes and humans compared to other primate species. Within hominid species, there are variations in the depth and aspect of their hand motor area, or knob, within the precentral gyrus. In this study, we used post-image analyses on magnetic resonance images to characterize the central sulcus shape of humans, chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), and orangutans (Pongo pygmaeus and Pongo abelii). Using these data, we examined the morphological variability of central sulcus in hominids, focusing on the hand region, a significant change in human evolution. We show that the central sulcus shape differs between great ape species, but all show similar variations in the location of their hand knob. However, the prevalence of the knob location along the dorso-ventral plane and lateralization differs between species and the presence of a second ventral motor knob seems to be unique to humans. Humans and orangutans exhibit the most similar and complex central sulcus shapes. However, their similarities may reflect divergent evolutionary processes related to selection for different positional and habitual locomotor functions.

Systemic AL kappa chain amyloidosis in a captive Bornean orangutan (Pongo pygmaeus)

Systemic amyloid light-chain (AL) amyloidosis is an infrequent disease in which amyloid fibrils derived from the immunoglobulin light chain are deposited in systemic organs, resulting in functional impairment. This disease has been notably uncommon in animals, and nonhuman primates have not been reported to develop it. In this study, we identified the systemic AL kappa chain amyloidosis in a captive Bornean orangutan (Pongo pygmaeus) and analyzed its pathogenesis. Amyloid deposits were found severely in the submucosa of the large intestine, lung, mandibular lymph nodes, and mediastinal lymph nodes, with milder lesions in the liver and kidney. Mass spectrometry-based proteomic analysis revealed an abundant constant domain of the immunoglobulin kappa chain in the amyloid deposits. Immunohistochemistry further confirmed that the amyloid deposits were positive for immunoglobulin kappa chains. In this animal, AL amyloidosis resulted in severe involvement of the gastrointestinal submucosa and lymph nodes, which is consistent with the characteristics of AL amyloidosis in humans, suggesting that AL amyloid may have a similar deposition mechanism across species. This report enhances the pathological understanding of systemic AL amyloidosis in animals by providing a detailed characterization of this disease based on proteomic analysis.

The complete sequence and comparative analysis of ape sex chromosomes

Apes possess two sex chromosomes—the male-specific Y chromosome and the X chromosome, which is present in both males and females. The Y chromosome is crucial for male reproduction, with deletions being linked to infertility1. The X chromosome is vital for reproduction and cognition2. Variation in mating patterns and brain function among apes suggests corresponding differences in their sex chromosomes. However, owing to their repetitive nature and incomplete reference assemblies, ape sex chromosomes have been challenging to study. Here, using the methodology developed for the telomere-to-telomere (T2T) human genome, we produced gapless assemblies of the X and Y chromosomes for five great apes (bonobo (Pan paniscus), chimpanzee (Pan troglodytes), western lowland gorilla (Gorilla gorilla gorilla), Bornean orangutan (Pongo pygmaeus) and Sumatran orangutan (Pongo abelii)) and a lesser ape (the siamang gibbon (Symphalangus syndactylus)), and untangled the intricacies of their evolution. Compared with the X chromosomes, the ape Y chromosomes vary greatly in size and have low alignability and high levels of structural rearrangements—owing to the accumulation of lineage-specific ampliconic regions, palindromes, transposable elements and satellites. Many Y chromosome genes expand in multi-copy families and some evolve under purifying selection. Thus, the Y chromosome exhibits dynamic evolution, whereas the X chromosome is more stable. Mapping short-read sequencing data to these assemblies revealed diversity and selection patterns on sex chromosomes of more than 100 individual great apes. These reference assemblies are expected to inform human evolution and conservation genetics of non-human apes, all of which are endangered species.

No immediate attentional bias towards or choice bias for male secondary sexual characteristics in Bornean orang-utans (Pongo pygmaeus).

Primate faces provide information about a range of variant and invariant traits, including some that are relevant for mate choice. For example, faces of males may convey information about their health or genetic quality through symmetry or facial masculinity. Because perceiving and processing such information may have bearing on the reproductive success of an individual, cognitive systems are expected to be sensitive to facial cues of mate quality. However, few studies have investigated this topic in non-human primate species. Orang-utans are an interesting species to test mate-relevant cognitive biases, because they are characterised by male bimaturism: some adult males are fully developed and bear conspicuous flanges on the side of their face, while other males look relatively similar to females. Here, we describe two non-invasive computerised experiments with Bornean orang-utans (Pongo pygmaeus), testing (i) immediate attention towards large flanges and symmetrical faces using a dot-probe task (N = 3 individuals; 2F) and (ii) choice bias for pictures of flanged males over unflanged males using a preference test (N = 6 individuals; 4F). In contrast with our expectations, we found no immediate attentional bias towards either large flanges or symmetrical faces. In addition, individuals did not show a choice bias for stimuli of flanged males. We did find exploratory evidence for a colour bias and energy efficiency trade-offs in the preference task. We discuss our null results and exploratory results in the context of the evolutionary history of Bornean orang-utans, and provide suggestions for a more biocentric approach to the study oforang-utan cognition.

Capacity for recovery in Bornean orangutan populations when limiting offtake and retaining forest

AbstractAimWe assess the potential long‐term viability of orangutan populations across Borneo, considering the effects of habitat loss, and various forms of population reduction, including hunting, retaliatory killings and capture and translocation.LocationThe study focused on the island of Borneo, a region that has experienced substantial deforestation over the past four decades, resulting in the degradation and fragmentation of its lowland forests, thereby threatening the island's unique biodiversity, including orangutan populations.MethodsTo evaluate the long‐term viability of orangutan populations, we employed a spatially explicit individual‐based model. This model allowed us to simulate various scenarios, including the impact of removing habitat fragments or individuals from the population.ResultsOur findings revealed that small forest fragments facilitate orangutan movement, thereby increasing the number of individuals settling in non‐natal patches. Crucially, orangutan populations proved highly vulnerable to even small levels of offtake. Annual removal rates exceeding 2% diminished the positive role of small forest patches in sustaining population connectivity, the long‐term viability of populations and prospects for recovery.Main ConclusionsOur results suggest that orangutan populations in Borneo could potentially recover from recent declines if removal of orangutans by hunting, retaliatory killings, capture and translocation is reduced, and habitat connectivity is maintained within human‐modified landscapes. These findings emphasize the urgent need for conservation strategies that mitigate negative human–wildlife interactions, and/or help preserve habitat and fragments as stepping stones. Measures could include promoting coexistence with local communities and translocating orangutans only in rare cases where no suitable alternative exists, to ensure the long‐term survival of orangutan populations in Borneo.

Vocal complexity in the long calls of Bornean orangutans.

Vocal complexity is central to many evolutionary hypotheses about animal communication. Yet, quantifying and comparing complexity remains a challenge, particularly when vocal types are highly graded. Male Bornean orangutans (Pongo pygmaeus wurmbii) produce complex and variable "long call" vocalizations comprising multiple sound types that vary within and among individuals. Previous studies described six distinct call (or pulse) types within these complex vocalizations, but none quantified their discreteness or the ability of human observers to reliably classify them. We studied the long calls of 13 individuals to: (1) evaluate and quantify the reliability of audio-visual classification by three well-trained observers, (2) distinguish among call types using supervised classification and unsupervised clustering, and (3) compare the performance of different feature sets. Using 46 acoustic features, we used machine learning (i.e., support vector machines, affinity propagation, and fuzzy c-means) to identify call types and assess their discreteness. We additionally used Uniform Manifold Approximation and Projection (UMAP) to visualize the separation of pulses using both extracted features and spectrogram representations. Supervised approaches showed low inter-observer reliability and poor classification accuracy, indicating that pulse types were not discrete. We propose an updated pulse classification approach that is highly reproducible across observers and exhibits strong classification accuracy using support vector machines. Although the low number of call types suggests long calls are fairly simple, the continuous gradation of sounds seems to greatly boost the complexity of this system. This work responds to calls for more quantitative research to define call types and quantify gradedness in animal vocal systems and highlights the need for a more comprehensive framework for studying vocal complexity vis-à-vis graded repertoires.

The relationship between Bornean orangutans’ (Pongo pygmaeus) population and land cover change in West Kalimantan, Indonesia

The relationship between Bornean orangutans’ (Pongo pygmaeus) population and land cover change in West Kalimantan, Indonesia

Oxygen isotopes in orangutan teeth reveal recent and ancient climate variation

Studies of climate variation commonly rely on chemical and isotopic changes recorded in sequentially produced growth layers, such as in corals, shells, and tree rings, as well as in accretionary deposits—ice and sediment cores, and speleothems. Oxygen isotopic compositions (δ18O) of tooth enamel are a direct method of reconstructing environmental variation experienced by an individual animal. Here, we utilize long-forming orangutan dentitions (Pongo spp.) to probe recent and ancient rainfall trends on a weekly basis over ~3–11 years per individual. We first demonstrate the lack of any consistent isotopic enrichment effect during exclusive nursing, supporting the use of primate first molar teeth as environmental proxies. Comparisons of δ18O values (n=2016) in twelve molars from six modern Bornean and Sumatran orangutans reveal a high degree of overlap, with more consistent annual and bimodal rainfall patterns in the Sumatran individuals. Comparisons with fossil orangutan δ18O values (n=955 measurements from six molars) reveal similarities between modern and late Pleistocene fossil Sumatran individuals, but differences between modern and late Pleistocene/early Holocene Bornean orangutans. These suggest drier and more open environments with reduced monsoon intensity during this earlier period in northern Borneo, consistent with other Niah Caves studies and long-term speleothem δ18O records in the broader region. This approach can be extended to test hypotheses about the paleoenvironments that early humans encountered in southeast Asia.

Oxygen isotopes in orangutan teeth reveal recent and ancient climate variation.

Studies of climate variation commonly rely on chemical and isotopic changes recorded in sequentially produced growth layers, such as in corals, shells, and tree rings, as well as in accretionary deposits-ice and sediment cores, and speleothems. Oxygen isotopic compositions (δ18O) of tooth enamel are a direct method of reconstructing environmental variation experienced by an individual animal. Here, we utilize long-forming orangutan dentitions (Pongo spp.) to probe recent and ancient rainfall trends on a weekly basis over ~3-11 years per individual. We first demonstrate the lack of any consistent isotopic enrichment effect during exclusive nursing, supporting the use of primate first molar teeth as environmental proxies. Comparisons of δ18O values (n=2016) in twelve molars from six modern Bornean and Sumatran orangutans reveal a high degree of overlap, with more consistent annual and bimodal rainfall patterns in the Sumatran individuals. Comparisons with fossil orangutan δ18O values (n=955 measurements from six molars) reveal similarities between modern and late Pleistocene fossil Sumatran individuals, but differences between modern and late Pleistocene/early Holocene Bornean orangutans. These suggest drier and more open environments with reduced monsoon intensity during this earlier period in northern Borneo, consistent with other Niah Caves studies and long-term speleothem δ18O records in the broader region. This approach can be extended to test hypotheses about the paleoenvironments that early humans encountered in southeast Asia.