Orangutan Behavior Research Articles

Identification of food type and feeding behavior of sumatran orangutans (Pongo abelii) at the Ketambe Research Station in Gunung Leuser National Park

As an endangered animal, sumatran orangutans ( Pongo abelii ) in Indonesia are declining rapidly. The extinction of food sources that formerly supported their diets is one of the factors that has contributed to this predicament. This paper aims to discover sumatran orangutans’ food types and feeding behaviors at the Ketambe Research Station, Aceh Province, Indonesia. Two orangutans, Chris and Kelly, were the subjects of this study, and their behavior and environment were observed and recorded using the focal animal sampling approach. The study uncovered 29 distinct forms of food (27 plant species and 2 insect species). The type of fruit most consumed by sumatran orangutans ( Pongo abelii ) at the Ketambe Research Station is Ficus racemosa, followed by Ficus obscura, Pandanus sp., and Ficus variegata. The type of leaf most consumed by sumatran orangutans ( Pongo abelii ) is Loides cirrosa, followed by Acacia pennata and Sindapsus hederaceus. Then, their eating behavior patterns cover choosing, holding, taking, and eating the food. The orangutans like eating their meal high up in a tree. As they lead semi-solitary, arboreal lifestyles, preserving the forest ecosystems in which they thrive is crucial.

A 50 year decennial survey of male Bornean orangutans (Pongo pygmaeus wurmbii) with supplemental genetic analysis in Tanjung Puting National Park, Indonesia

Abstract. Galdikas BM, Linsky RE, Djojoasmoro R, Lorenz J, Wagner RS. 2023. A 50 year decennial survey of male Bornean orangutans (Pongo pygmaeus wurmbii) with supplemental genetic analysis in Tanjung Puting National Park, Indonesia. Biodiversitas 24: 2587-2595. This study investigates the declining presence of adult males in a protected wild population of Bornean orangutans (Pongo pygmaeus wurmbii) at the Camp Leakey study area in Tanjung Puting National Park (TPNP), Central Kalimantan, Indonesian Borneo. Orangutan populations are in decline due to habitat destruction and fragmentation. Documenting changes within existing orangutan populations over time is important to understand demographic changes that may indicate pre-extinction processes and imminent collapse. Wild orangutan behavior has been studied at Camp Leakey since 1971. Observations of orangutans over the past five decades have documented a greatly decreased number of encounters with flanged adult males. A supplementary six-month genetic study was hindered by the fact that only two adult males briefly appeared in the study area in 2016 as compared to 40 adult male encounters in the same time period in 1976. The decline which appears most visible in data from 1986 to 1996 continues into 2006 and 2016. Genotypes from 24 wild adult orangutans encountered in 2016 were analyzed to assess the expected genetic parameters of a wild orangutan population. Pairwise relatedness was high among and between adult females and subadult males. The only two flanged males present during the genetic survey shared zero pairwise relatednesses. However, both flanged males had non-zero pairwise relatedness with other members of the Camp Leakey community and thus it is likely they were from different local areas. These data show the genetic consequences of the observed demographic changes. As TPNP forests have become disconnected from neighboring habitats, natural orangutan male dispersal may be disrupted. Disruption of male dispersal would increase the risk of accelerated extirpation for the orangutan population in TPNP as well as other orangutan populations, especially those that are remnant and less protected.

Individual Behavior Of Female Sumatran Orangutan (Pongo abelii L.) With Enclosure Management System In Siantar Zoo

Sumatran orangutans (Pongoabelii L.) is an endangered species due to habitat destruction. Conservation strategies need to be done in preventing extinction of orangutans, such as ex-situ conservation in Siantar zoo. This study aims to determine the behavior of individual male orangutan at Siantar Zoo with a management system. The observatuons was conducted for 14 days in August with the Focal Animal Sampling method, data recorded using the Instantaneous method and descriptive data using the Open Ended interview technique. The results showed the overall frequency of individual male orangutan behavior were locomotion (33,43%), resting (27,36%), eating (25,24%), playing (9%), agonistic (3,64%), self care (0,83%) and pooping (0,5%). The behavior of individual male orangutan is influenced by the number of visitors, namely the locomotion behavior of the crowded visitor category (34,37%), medium (30,31%) and quiet (33,18%). The resting behavior of crowded visitor catego ry (25,02%), medium (28,19%) and quiet (27,44%). The eating behavior for crowded, medium and quiet categories was 25,96% ; 25,47% and 26,30%. The playing behavior in crowded, medium and quiet categories is 7,96% ; 7,71% ; 9,75%. Agonistic behavior in crowded categories (5,44%), medium (7,11%) and quiet ( 1,96%). Self-care behavior for crowded,medium and quiet categories was 0,64% ; 0,83% ; 0,88%. The pooping behavior in the crowded category is 0,59%, in the medium category is 0,38% and in the quiet category is 0,49%. Themanagement system for male orangutan at Siantar Zoo already has a fairly good and regular system. The cage management has met the minimum requirements and the male orangutan has a optimal body weight and has never been infected with a serious disease.

Individual Behavior Of Female Sumatran Orangutan (Pongo abelii L.) With Management System In Siantar Zoo

The Sumatran orangutan (Pongo abelii) is an endangered species due to the destruction of its forest habitat and deforestation. Various conservation efforts have been made to prevent the orangutan extinction,such as ex-situ conservation in Siantar Zoo.This study aims to determine the behavior of individual female orangutans at Siantar Zoo with a management system. The observatuons was conducted for 14 days in August with the focal animal sampling method and data recorded using the Instantaneous method.The results showed the overall frequency of individual female orangutan behavior were resting (40%), eating (35%), moving (14%), special (6%), self care (4%) and pooping (1%). The behavior of individual female orangutans is influenced by the number of visitors, namely the resting behavior of the crowded visitor category 39,15%, medium category 41.81% and quiet 39.68%. The eating behavior of the crowded visitor category is 37.80%, the medium category is 33.56% and the quiet category is 34.68%. The moving behavior in the quiet, medium and crowded categories is 14.18%; 12.85%; 11.67%. The specific behavior for the quiet, medium and crowded categories was 6.19%; 5.55%; 5.59%. Self-care behavior in the crowded visitor category is 4.34%, the medium category is 4.60% and the quiet category is 4.01%. The behavior of pooping in the crowded category is 1.45%, in the medium category is 1.62% and in the quiet category is 1.27%.The female orangutan management system at Siantar Zoo is analyzed as having a fairly good and regular system. The cage management has met the minimum requirements and the female orangutan has a good body weight and has never been infected with a serious disease.

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.

After the smoke has cleared: Extended low fruit productivity following forest fires decreased gregariousness and social tolerance among wild female Bornean orangutans (Pongo pygmaeus wurmbii)

As climate change continues to fundamentally alter resource landscapes, the ability to flexibly respond to spatio-temporal changes in the distribution of preferred food sources is increasingly important for the overall health and fitness of animals living in seasonal, variable, and/or changing environments. Here, we investigate the effects of an uncharacteristically long period of fruit scarcity, following widespread thick haze caused by peat and forest fires in 2015, on the behaviour and sociality of female Bornean orangutans (Pongo pygmaeus wurmbii). We collected data from 2010 to 2018 at Tuanan, Central Kalimantan, Indonesia, and compared the activity, diet, and association patterns of adult females during low-fruit periods before the fires, i.e., regular, seasonal periods of low fruit availability (“pre-fire”), and after the fires, i.e., during the extended period of low fruit availability (“post-fire”). First, we found that, post-fire, female orangutans adopted a more extreme energy-saving activity pattern and diet — resting more, travelling less, and diet-switching to less-preferred foods — compared to pre-fire. Second, we found that the probabilities of association between females and their weaned immature offspring, and between related and unrelated adult females were lower, and the probability of agonism between unrelated females was higher, post-fire than pre-fire. This change in energetic strategy, and the general reduction in gregariousness and social tolerance, demonstrates how forest fires can have lasting consequences for orangutans. Fission–fusion species such as orangutans can mitigate the effects of changes in resource landscapes by altering their (sub)grouping patterns; however, this may have long-term indirect consequences on their fitness.

Population Status of Tapanuli Orangutan (Pongo tapanuliensis) within the Renewable Energy Development and its Management Implications

To protect Tapanuli orangutan it is essential to understand the actual situation. It has been studied 15% of its population live outside the protected area facing a density disruption due to forest conversion. Several best management practices have been created and tested for different natural concession types. Yet, the main objective to reduce the impact and increase wildlife survival is far away from the goal. To improve our understanding of the species survival within ongoing project construction, we conducted population density monitoring prior- to post-construction time frames within the hydroelectric dam project. Also, we carried out spatial analysis to understand the land cover change and orangutan’s suitable habitat distribution. This study found that during high construction activities, orangutans were avoiding the threat sources, and returned when the disturbances reduced. These findings indicated orangutans are ecology flexible and have the capability to increase its survival, although the company’s involvement is crucial to facilitate the successes. Our study is based on indirect observation, and spatial modeling, which may lead to an uncertain conclusion. Further research on orangutan ecology and behavior is prioritized.

Habitat fragmentation effect on the characteristics of orangutan nest tree selection

Orangutans are an endemic to Indonesia and Malaysia with an almost extinct with critically endangered status and only found on the islands of Sumatra and Kalimantan/Borneo. Orangutan extinction is mainly threat by habitat loss and fragmentation as well as low reproduction rates. Habitat fragmentation, along with habitat loss, should be clearly considered when assessing implications of landscape change for population extinctions. Environmental changes force species to immediately adapt both behaviourally and physiologically. Forest structure affects the adaptability and nesting behaviour of orangutans. One of the steps to prevent orangutan extinction is by increasing habitat connectivity through corridors and reducing fragmentation of landscapes as well as stopping habitat lost.

The Gunung Palung Orangutan Project: Twenty-five years at the intersection of research and conservation in a critical landscape in Indonesia

The Gunung Palung Orangutan Project has conducted research on critically endangered wild Bornean orangutans (Pongo pygmaeus wurmbii) since 1994 in Gunung Palung National Park, West Kalimantan, Indonesia. A major goal of our broad-ranging research on orangutan behavior and ecology is to understand how the unique rainforest environment of Southeast Asia, characterized by dramatic changes in fruit productivity due to unpredictable mast fruiting, impacts orangutan behavior, physiology, and health. Much of our research has been devoted to the development of non-invasive techniques and an integrated biology approach – using hormonal assays, fecal processing, nutritional analysis, genetics, and behavioral ecology – and has led to an increased understanding of the ecological and evolutionary pressures shaping orangutan adaptations. Our results show that the extended life history and very slow reproductive rate of orangutans are adaptations to their environment. Orangutans in the Gunung Palung landscape, as elsewhere across Borneo and Sumatra, also face a series of conservation challenges, including extensive habitat loss and the illegal pet trade. We highlight how our investigations of orangutan health status, ecosystem requirements, and the assessment of orangutan density using ground and drone nest surveys have been applied to conservation efforts. We describe our project's direct conservation interventions of public education and awareness campaigns, sustainable livelihood development, establishment of village-run customary forests, investigation of the illegal pet trade, and active engagement with Indonesian government organizations. These efforts, in concert with the development of local scientific and conservation capacity, provide a strong foundation for further conservation as orangutans face a challenging future.

An evaluation of interactive projections as digital enrichment for orangutans.

Digital technologies are increasingly being incorporated into the provision of enrichment for captive primates, ranging from the ad-hoc use of iPads to specifically designed hardware installed in the design of new exhibits. In this article, we present a digital enrichment system that utilizes a novel approach with interactive projections, installed in the orangutan exhibit at Melbourne Zoo. While previous research into orangutan enrichment has involved reinforcement using food rewards, this study is the first investigation of digital enrichment for orangutans that does not involve food rewards. Rather, the interactive projections were designed to provide intrinsically rewarding environmental enrichment, instead of a cheaper or more variable way of delivering food. Our observations of orangutans' use of the system supports the approach of using interactive projections, finding that it is more responsive than capacitance or resistive based touch-screen technologies to the variety of ways that orangutans "touch": with whole hands, feet, faces, and with objects. We also present the results from a preliminary study into the effect of this enrichment into orangutan behavior which found presence or use of the device did not affect time spent engaged in the majority of behaviors of the individuals studied.

Dinamika Perilaku Orangutan Kalimantan (Pongo pygmaeus wurmbii) di Taman Nasional Sebangau Kalimantan Tengah

Sebangau National Park represents a relatively intact peatland ecosystem and is one of the pockets of the P.p. ssp. wurmbii crucial in the world. Anthropological studies state that Orangutans have a social unit in a complex structure. The logical consequence of this condition is that many observed behaviors attract and open up new knowledge related to space use patterns. This study aims to uncover the dynamics of orangutan behavior by presenting critical evidence. This research is a descriptive exploratory study, using a non-invasive observation method with a camera trap approach, in the Punggualas area, from January 2012 to January 2014. The results show confirmation of walking on the forest floor as a new part of the orangutan association of behavior. Based on this, the conclusion drawn is that the dynamics of orangutan behavior develop dynamically in response to changes in natural habitat conditions.

Behavior Of Individual Orangutan Sumatera (Pongo Abelii) Before Direintroduction At The Orangutan Quarantine Station, Sibolangit, Deli Serdang, North Sumatera

The individual behavior of orangutan (Pongoabeli) before reintroduction to the wild was studied from March to June 2012 in orangutan quarantine station Batumbelin Sibolangit, Deli Serdang. The research used focal animal sampling method, at the same time the data recording was taken using instantenous method. The result showed that solitary behavior (39.34%) which was dominated by feeding (20.60%). The second highest (35.31%) was resting which was dominating by sitting (16.87%) followed by moving behavior (13.58%) which mostly was branching (7.54%). The least activity was competitive behavior (1.88%) which was dominated by streaking down each other (0.82%). The result also indicated an abnormal behavior among 3 orangutans observed such as eating their own feces.

Proximate mechanisms and relational history: the interdependence of food transfers in socially housed orang-utans (Pongo abelii)

Animals can transfer food between each other through both competition (theft) and cooperation (sharing). Analysing patterns of food transfers can thus yield valuable insights into animals’ social dynamics, e.g. intragroup competition and cooperation. Previous studies on food transfers in our closest living relatives, the great apes, have mainly focused on ultimate explanations for food sharing and analysed food transfers as independent events with a focus on frequencies and types of transfers. In this study, we focus on the influence of contextual variables and the directly preceding interaction on food transfer attempts. We provided one monopolizable food bag per session (10 sessions each in 2010, 2012, 2014 and 2016) to orang-utans housed in the same enclosure ( N = 12) and coded the subsequent transfers and transfer attempts of food items from the bag ( N = 3207). We divided transfer attempts into four different categories (taking, co-feeding, requests, offers) and found comparable frequencies as in previous studies on food sharing in great apes. We present four models that investigate to what extent food transfer attempts influence the subsequent transfer attempt within a dyad with regards to probability of a successful transfer, choice of transfer strategy, time between two transfer attempts and probability of resistance by the food possessor. Our analyses show that characteristics of the previous interactions (e.g. success, resistance by the food possessor) and the current interaction (e.g. being in view of the food possessor, food location) affected both the behaviour of the initiator of a transfer attempt and of the food possessor. These results highlight how the behaviour of orang-utans is influenced by the preceding interaction within a dyad and by several other context-specific cues. This shows that orang-utans keep track of their most recent interaction with the same partner and take that into account towards calibrating their next interactional moves. • Orang-utans flexibly used cooperative and competitive strategies to transfer food. • Proximate mechanisms explain changes in strategies, delays, success and resistance. • Food transfers within a dyad were not independent events. • Food transfers were influenced by the preceding interaction within each dyad. • These results reveal orang-utans’ cognitive flexibility and relational intelligence.

My life among the apes.

I have spent over 40 years studying the behavior of our closest living relatives, the apes. In this paper, I review my research on the spacing, mating, and vocal behavior of gibbons and orangutans (Pongo pygmaeus) and the vocal and social behavior of chimpanzees (Pan troglodytes). I devote special attention to results derived from a 25-year-long study of a remarkable and extraordinarily large group of chimpanzees that has recently fissioned at Ngogo in Kibale National Park, Uganda. I conclude with some advice for the next generation of field primatologists.

PERILAKU MAKAN DAN JENIS PAKAN ORANGUTAN (Pongo pygmaeus) DI HUTAN DESA GURUNG MALI KECAMATAN TEMPUNAK KABUPATEN SINTANG

The condition of orangutan habitat in ex-situ conservation areas is different from the condition of their natural habitat. These different habitat conditions will have an impact on orangutan behavior, especially food behavior and selection of feed types. This study aims to determine the feeding behavior and the food types of orangutans (Pongo pygmaeus) in the Forest Of Gurung Mali Village Tempunak Sub-district Sintang District. Observation of eating behavior is done using the focal animal sampling method. Observation of eating activities is quantitative, namely recording the time taken during orangutan eating activities. Observation of the type of feed is done by observing the remnants of discarded plants found on the forest floor and trees found as a place for orangutans looking for food sources. Based on observations of the eating behavior of each individual orangutan for the food provided shows the behavior of eating while sitting is higher than the percentage of other eating behavior. For the eating behavior that they are looking for themselves, it shows that Oscar, Digo and Putri tanjung individuals have higher hanging behavior compared to other eating behaviors. The percentage of Momo and Jojo individuals sat higher eating behavior compared to the percentage of other eating behaviors. The types of feed found in the study site were found 8 types of feed provided by the Rehabilitation center and 24 types of natural food contained in the enclosure forest.Keywords : Feeding Behavior, Orangutan, Type of Feed.

AKTIVITAS SOSIAL ORANGUTAN (Pongo pygmaeus wurmbii) DI STASIUN PENELITIAN CABANG PANTI TAMAN NASIONAL GUNUNG PALUNG KABUPATEN KAYONG UTARA KALIMANTAN BARAT

Diverse types of habitat were interesting objects which existed in the Cabang Panti Research Station, due to it, the researcher was interested to investigate about Orangutan’s activities in one type of habitat and the researcher focused on Orangutan’s social activities. The purpose of this study was to determine the social behavior of orangutans in the Research Station cabang panti gunung palung national park in Kayong Utara District, West Kalimantan. The used method was focal animal sampling, a method of observing and recording the behavior of one individual over a certain period of time while the object must be visible during observation and the data collection in this study focused on adult male and / or female orangutans as the objects in the study. The length of observation time of the target orangutan in this study was + 13 hours per day for 5 days by concerning the daily activities of orangutans from waking up to sleeping. Based on the results of the observed object, there were 2 individuals namely Walimah which was an adult female and Julian which was an adult male. Overall, during the observations, the two individuals were following each other, the target orangutan “Walimah” had high eating activities throughout the day reaching 41,31% followed by movement activities 25,18%, then resting 23,18%, self-action 9,96%, and social activity 0,37%. While the target orangutan "Julian" carried out high resting activities throughout the day reaching 40,15% followed by eating activities 28,45%, movement 22,71%, self-action 7,73%, and social activity 0,97%.Keywords: Cabang Panti, Orangutan, Social Activity

Erratum to: Development and behavior of wild infant-juvenile East Bornean orangutans (Pongo pygmaeus morio) in Danum Valley.

Orangutans have a long period of immaturity and the longest inter-birth interval (IBI) of all mammals, which can be explained by their solitary life style, preventing the mother from rearing two offspring simultaneously (solitary life hypothesis) [corrected]. We collected data on mother-offspring dyads living in a primary lowland forest in Danum Valley, East Borneo in an effort to examine the developmental and behavioral patterns of the subspecies Pongo pygmaeus morio. We analyzed developmental changes in mother-offspring distance, contact, and activity budgets in orangutans ranging from 1 to 7 years of age. The results indicated decreased resting and playing with increasing age, whereas feeding, traveling and social play all increased significantly. Mothers' feeding and traveling time were good predictors of their offspring's feeding and traveling activities. Mother-offspring contact lasted longer in resting contexts; contact during traveling was almost non-existent after 4 years of age. Comparisons with previously published data on the Sumatran species Pongo abelli revealed no fundamental differences in these behavioral measures. However, a shorter association time with the mother after behavioral independence is documented for this East Bornean population in comparison to Sumatran populations. These results are best explained by the solitary life hypothesis, in agreement with previous studies. We suggest that environmental constraints in Bornean forests, as well as a lower population density, should be considered when interpreting the differences between Sumatran and Bornean orangutans in both the period of association with mother and the IBI.

Caregiver/Orangutan Relationships at Auckland Zoo

Drawing on ethnographic, ethological, and historical data, we examined the relationships between orangutans and caregivers at Auckland Zoo. Caregivers displayed high levels of empathy and adjusted their husbandry routines to their interpretations of the orangutans’ moods. Caregivers experienced conflicts arising from their efforts to empathize. Although they agreed their husbandry approach improved welfare, they worried their interpretations of orangutan behavior were inaccurate anthropomorphic projections. However, caregivers’ interpretations aligned well with ethological observations and with current knowledge of orangutan behavior. Caregivers’ shared view of great apes as moral persons led to personal conflicts about the ethics of sacrificing individual orangutans’ freedom for the greater good of the species. By exploring caregivers’ personal conflicts, we aimed to inform debates about the politics of empathizing with animals, the role of zoos, and the ethics of keeping great apes in captivity. We argue the use of empathy is essential for engaging in intersubjective relationships.

Orangutan behavior in Kutai National Park after drought and fire damage: Adjustments to short- and long-term natural forest regeneration.

This study aimed to develop a long-term picture of orangutan (Pongo pygmaeus morio) behavioral adjustments to damaged masting forest around Mentoko, Kutai National Park, Indonesia. Mentoko is regenerating from two severe burnings and is one of few areas where orangutans were well-studied before and early after damage. We studied orangutans' feeding ecology, diet, and activity budgets 12-15 years after the second burning then compared our findings with earlier pre- and post-damage ones to assess the changes and factors involved. By our study, we predicted (1) improved feeding ecology compared to early in regeneration, (2) behavior diverging from the normal foraging strategy and (3) behavior shifting toward pre-damage patterns with improving feeding ecology. Data were behavioral observations on 42 orangutans (422 full day follows, 3,522 hr) and tree plot measures of feeding ecology. Findings were consistent with the first and third predictions but not the second: (1) feeding ecology had improved (plant food abundance was near per-damage levels, but species composition had changed); (2) foraging strategies showed no divergence from normal (fallback-preferred food switches in diet and activity budget adjustments were both normal, notably travel did not reduce), (3) diet and activity budgets had reverted to near pre-damage values by our study. Differently than post-damage studies on other orangutans but consistent with those on other primates, our comparisons showed behavioral adjustments were flexible, multiple vs. single, and influenced by multiple factors. Factors likely involved at Mentoko include type and spatial configuration of damage, duration of regeneration, and P. p. morio's recognized resilience. Findings have value for orangutan and nature conservation in showing that recovery to near-normal levels from severe habitat damage is possible within ca 15 years and in adding to understanding of the factors and processes that contribute to recovery.

OrangFACS: A Muscle-Based Facial Movement Coding System for Orangutans (Pongo spp.)

Comparing homologous expressions between species can shed light on the phylogenetic and functional changes that have taken place during evolution. To assess homology across species we must approach primate facial expressions in an anatomical, systematic, and standardized way. The Facial Action Coding System (FACS), a widely used muscle-based tool for analyzing human facial expressions, has recently been adapted for chimpanzees (Pan troglodytes: ChimpFACS), rhesus macaques (Macaca mulatta: MaqFACS), and gibbons (GibbonFACS). Here, we present OrangFACS, a FACS adapted for orangutans (Pongo spp.). Orangutans are the most arboreal and the least social great ape, so their visual communication has been assumed to be less important than vocal communication and is little studied. We scrutinized the facial anatomy of orangutans and coded videos of spontaneous orangutan behavior to identify independent movements: Action Units (AUs) and Action Descriptors (ADs). We then compared these facial movements with movements of homologous muscles in humans, chimpanzees, macaques, and gibbons. We also noted differences related to sexual dimorphism and developmental stages in orangutan facial morphology. Our results show 17 AUs and 7 ADs in orangutans, indicating an overall facial mobility similar to that found in chimpanzees, macaques, and gibbons but smaller than that found in humans. This facial movement capacity in orangutans may be the result of several, nonmutually exclusive explanations, including the need for facial communication in specialized contexts, phylogenetic inertia, and allometric effects.