Adult Male Orangutan Research Articles

“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.

Wild Bornean orangutans experience muscle catabolism during episodes of fruit scarcity

Pronounced temporal and spatial variation in the availability of food resources can produce energetic deficits in organisms. Fruit-dependent Bornean orangutans face extreme variation in fruit availability and experience negative energy and protein balance during episodes of fruit scarcity. We evaluate the possibility that orangutans of different sexes and ages catabolize muscle tissue when the availability of fruit is low. We assess variation in muscle mass by examining the relationship between urinary creatinine and specific gravity and use the residuals as a non-invasive measure of estimated lean body mass (ELBM). Despite orangutans having a suite of adaptations to buffer them from fruit scarcity and associated caloric deficits, ELBM was lower during low fruit periods in all age-sex classes. As predicted, adult male orangutans had higher ELBM than adult females and immatures. Contrary to expectation, flanged and unflanged males did not differ significantly in ELBM. These findings highlight the precarity of orangutan health in the face of rapid environmental change and add to a growing body of evidence that orangutans are characterized by unique metabolic traits shaped by their unpredictable forest environment.

Morphometric, Behavioral, and Genomic Evidence for a New Orangutan Species

Six extant species of non-human great apes are currently recognized: Sumatran and Bornean orangutans, eastern and western gorillas, and chimpanzees and bonobos [1]. However, large gaps remain in our knowledge of fine-scale variation in hominoid morphology, behavior, and genetics, and aspects of great ape taxonomy remain in flux. This is particularly true for orangutans (genus: Pongo), the only Asian great apes and phylogenetically our most distant relatives among extant hominids [1]. Designation of Bornean and Sumatran orangutans, P.pygmaeus (Linnaeus 1760) and P.abelii (Lesson 1827), as distinct species occurred in 2001 [1, 2]. Here, we show that an isolated population from Batang Toru, at the southernmost range limit of extant Sumatran orangutans south of Lake Toba, is distinct from other northern Sumatran and Bornean populations. By comparing cranio-mandibular and dental characters of an orangutan killed in a human-animal conflict to those of 33 adult male orangutans of a similar developmental stage, we found consistent differences between the Batang Toru individual andother extant Ponginae. Our analyses of 37 orangutan genomes provided a second line of evidence. Model-based approaches revealed that the deepestsplit in the evolutionary history of extant orangutans occurred ∼3.38 mya between the Batang Toru population and those to the north of Lake Toba,whereas both currently recognized species separated much later, about 674 kya. Our combinedanalyses support a new classification of orangutans into three extant species. The new species, Pongo tapanuliensis, encompasses the Batang Toru population, of which fewer than 800 individuals survive. VIDEO ABSTRACT.

Quantity matching by an orangutan (Pongo abelii)

An adult male orangutan (Pongo abelii) was presented with a series of delayed matching-to-sample (DMTS) tasks in which he was to match images based on (a) the number of individual animals depicted in the photograph (from 1 to 4), (b) the number of abstract shapes presented in the stimulus (from 1 to 4), or (c) the number of dots presented in the stimulus (from 1 to 4, 4-7, or 7-10). The spatial arrangement of the dots and the background color of the stimuli varied, and the size of the dots was manipulated to control for overall ratio of foreground to background. The subject's performance was not affected by these perceptual features, but was affected by the absolute difference and ratio between number of elements in the comparison stimuli. However, the relationship between these variables and his performance was not always linear as predicted by the analog magnitude model. In addition, the subject showed a high degree of transfer to novel numerosities up to ten, indicating that orangutans are capable of estimating quantity for a greater number of items than can presumably be subtilized by humans.

Vergesellschaftung als Verhaltensbereicherung im Zoo – Soziale Interaktion und Raumnutzung bei Orang-Utans, Hulmans und Kurzkrallenottern in der Zoom Erlebniswelt Gelsenkirchen

Keeping different species together is getting more and more common in zoos, because it can entail several behavioural enrichment factors for the animals as long as the enclosure meets the requirements of all species and a suitable composition of animals is living in the mix. The aim of this study is to evaluate a community of Sumatran orangutans (Pongo abelii), northern plains grey langurs (Semnopithecus entellus) and Asian small-clawed otters (Aonyx cinerea) in the Zoological Garden of Gelsenkirchen.The behavioural monitoring of the animals reveals that the orangutans spend less time with feeding behaviour and locomotion than free ranging orangutans, whereas the percentage of resting periods is much higher. This difference is probably caused by the easy availability of food. The northern plains grey langurs show ethograms whose proportions are very similar to those of free ranging grey langurs in literature. In both species the juvenile individuals have higher activity levels than the adult animals.The analysis of the spatial use of the enclosure by the orangutans reveals that they use about half of the area and prefer places at the ground for resting. On an average the orangutans spend around 50% of the monitored situations on the ground which is a high level for an arboreal living species. The time spent on the ground is distinctly lower in orangutans reared by their parents than in hand reared individuals which are probably affected by humans. Another influencing point is the sex. Adult male orangutans spend more time on the ground. This is a fact which is also known from free ranging animals. Related to their environment free ranging northern plains grey langurs show a high adaptability and the individuals in the zoo use about 70% of the enclosure and use frequently all structuring elements like trees, roots and ropes. Like the orangutans the grey langurs have preferred areas in the enclosure where they spend their resting periods with grooming, lactating and the feeding periods. Generally, the Asian small-clawed otters spend less time in the enclosure than the monkeys and use less than one third of the area.Most of the time free ranging orangutans live solitarily and thus it was predictable that there is only a fraction of intraspecific interactions between orangutans whereas the percentage of interactions between langurs is higher. The northern plains grey langurs live in harem troops and social interactions are more than 40% of the zoo langur's ethogram on an average. Asian small-clawed otters are also highly social animals and intraspecific contacts take place very often.The analysis of the monitored interspecific interactions between all species reveals that the juvenile animals of both primate species have distinct more interspecific contacts than the adult animals. In most cases the interactions are positive or playful contacts. Especially between a 12-year-old female orang-utan and one of the juvenile langurs friendly interactions with body contact were monitored often. Between the adult animals agonistic contacts or submission are most common. The Asian small-clawed otters are very interested in the orangutans and often approach towards them to have a sniff or pull their hair.The community of all three species is quite harmonious and serves as behavioural enrichment for all individuals. For the visitors the mixed enclosure is a benefit as well.

Functional Anatomy and Adaptation of Male Gorillas (Gorilla gorilla gorilla) With Comparison to Male Orangutans (Pongo pygmaeus)

Great apes diversified during the Miocene in Old World forests. Two lineages, gorillas in Africa and orangutans in Asia, have sexual dimorphisms of super-sized males, though they presumably diverged from a smaller common ancestor. We test the hypothesis that they increased in body mass independently and convergently, and that their many postcranial differences reflect locomotor differences. Whole body dissections of five adult male gorillas and four adult male orangutans allowed quantification of body mass distribution to limb segments, of body composition (muscle, bone, skin, and fat relative to total body mass), and of muscle distribution and proportions. Results demonstrate that gorilla forelimb anatomy accommodates shoulder joint mobility for vertical climbing and reaching while maintaining joint stability during quadrupedal locomotion. The heavily muscled hind limbs are equipped for propulsion and weight-bearing over relatively stable substrates on the forest floor. In contrast, orangutan forelimb length, muscle mass, and joint construction are modified for strength and mobility in climbing, bridging, and traveling over flexible supports through the forest canopy. Muscles of hip, knee, and ankle joints provide rotational and prehensile strength essential for moving on unstable and discontinuous branches. We conclude that anatomical similarities are due to common ancestry and that differences in postcranial anatomy reflect powerful selection for divergent locomotor adaptations. These data further support the evolutionary conclusion that gorillas fall with chimpanzees and humans as part of the African hominoid radiation; orangutans are a specialized outlier.

Nerve Fibre Tracing of Branches to the Coracobrachialis Muscle in a Bornean Orangutan (Pongo pygmaeus pygmaeus)

A detailed anatomical analysis of the left brachial plexus, composed of the fourth cervical to first thoracic spinal nerve roots, was performed in an adult male orangutan obtained from the Osaka Museum of Natural History. Although the medial and posterior cords fused into a common trunk, a nerve fibre analysis revealed that the cords were not actually connected. A superficial branch (Rs) running ventral to the musculocutaneous nerve (MC) and a deep branch (Rp) running dorsal to the MC innervated the coracobrachialis muscle, which was also innervated by coracobrachialis branches (Rmc) from the MC. Koizumi (1989: Acta Anat. Nippon, 64, 18) reported that the Rmc and Rs innervated the superficial region of the coracobrachialis muscle corresponding to superficial coracobrachialis muscle in prosimians, whereas the Rp innervated the deep region. However, the detailed innervation of the coracobrachialis muscle in orangutans was not included in Koizumi and Sakai's (1995: J. Anat. 186, 395) report. Our observations in an orangutan did not seem to support generalisation, because the common trunk of the Rp and Rmc appeared to innervate both the superficial and deep regions of the coracobrachialis muscle. Therefore, a nerve fibre analysis of the common trunk was performed as a detailed examination. The analysis confirmed that the Rp in the orangutan only innervated the deep region of the coracobrachialis muscle, similar to the innervation pattern seen in other apes and humans.

Male bimaturism and reproductive success in Sumatran orang-utans

Although orang-utans live solitary lives most of the time, they have a complex social structure and are characterized by extreme sexual dimorphism. However, whereas some adult male orang-utans develop full secondary sexual characteristics, such as cheek flanges, others may stay in an “ arrested” unflanged condition for up to 20 years after reaching sexual maturity. The result is a marked bimaturism among adult males. Flanged males allow females to overlap with their home range and often tolerate the presence of unflanged males. However, wherever possible flanged males actively prevent unflanged males from copulating with females. Two competing hypotheses, previously untested, have been advanced to explain male reproductive behavior and bimaturism in orang-utans: (1) the “ range-guardian” hypothesis, which asserts that the flanged males are postreproductive and defend a range in which they tolerate sexually active, unflanged male relatives; and (2) the “female choice” hypothesis, which asserts that flanged males tolerate unflanged males in their range because they rely on female preference to favor flanged males. We investigated these hypotheses and a third hypothesis that the two male morphs represent co-existing alternative male reproductive strategies (“sitting, calling, and waiting” for flanged males versus “ going, searching, and finding” for unflanged males). Fecal samples were collected from a well-studied population in Indonesia, and eight human microsatellites were analyzed for 30 individuals that have been behaviorally monitored for up to 27 years. By carrying out paternity analysis on 11 offspring born over 15 years, we found that unflanged males fathered about half (6) of the offspring. Relatedness between successful unflanged males and resident dominant males was significantly lower than 0.5, and for some unflanged/flanged male pairs, relatedness values were negative, indicating that unflanged males are not offspring of the flanged males.

Brief communication: Weights of wild orang utans

Exact records of the weight of wild primates are of great value, even more so nowadays than formerly because of the extensive use of such data in allometric studies (see, for example, Kay, 1981; Pilbeam and Gould, 1974). Too few accurate records exist, and, in the case of a large ape like the orang utan (Pongo pygmaeus), it is difficult to obtain data on living examples and would be inappropriate, for both conservation and ethical reasons, to obtain any new data on further wild-killed specimens. It is, therefore, imperative to use what data we already have in the most accurate possible way. The only accurate weights for wild orang utans appear to be those of Abbott, as reported by Lyon (1907, 1908, 1911). These were analysed by Eckhardt (19751, who pointed out that a failure to transform avoirdupois to metric in the case of the Bornean specimens had resulted in a spurious disparity in subsequent literature between reported weights of Bornean and Sumatran subspecies ofP. pygmaeus. According to Eckhardt’s re-analysis, adult male orang utans (both subspecies together) range in weight from 32 to 91 kg and females from 32 to 46 kg (in rounded figures). His conclusions have been widely cited and have been utilised by such authors as Fooden and Izor (1983) in important growth studies. What is missing from Eckhardt’s study, and subsequent utilisation of it, is an appreciation of the degree to which orang utans, especially males, grow after achievement of formal maturity. According to Fooden and Izor (19831, the third molars erupt at about age 9 to 10 years; this being the traditional criterion of maturity, both Schultz (1941) and Eckhardt (1975) include as “adult” all specimens in which third molars are reported by Lyon (1908,1911) to have the third molars at least visible in their alveoli. From Fooden and Izor’s data (19831, however, it is clear that males continue to grow well into their teen years and females perhaps somewhat beyond 10 years of age. This we can confirm in a growth study in preparation. The delay in physical maturity beyond the apparently correlated achievement of sexual maturity has important behavioural consequences in this species (Galdikas, 1985). The question, then, is which of Abbott’s orangs, “adult” though they may formally have been, were actually fully grown? Lyon (especially in his 1908 paper) gives quite detailed information on the maturity of the skull, as well as the stage of dental eruption. One of us (C.P.G.) has examined the specimens in question, in the Smithsonian Institution (Natural History), Washington D.C., and independently verified these assessments. It is absolutely clear that Lyon’s sample included many that are far from mature and ought to be excluded from any sample purporting to represent the sizes of fully grown animals:

Morphology and relationships of the orangutan fatty cheek pads

The present paper examines the anatomical relationships as well as possible developmental and functional relationships of the fatty cheek pad characteristic of the adult male orangutan. The research involves the dissection of 11 orangutans of both sexes in a variety of age categories. All specimens possess either a fat pad or a subcutaneous connective tissue fascial compartment in the lateral face extending superiorly from slightly above the inferior border of the mandible to the temporal region. In immature specimens as well as adult females, fat deposits within the connective tissue compartment are scarce or nonexistent, whereas pubescent male specimens or older possess accumulations of fibro-fatty tissues in this region. The extensive fat accumulations of the adult male cheek flange are related to age and sex and to modifications in related facial musculature, especially mm. platysma, zygomaticus, orbicularis oculi, and orbitotemporalis and frontalis. These muscles are clearly related to the cheek pad structures in both sexes but appear to assume a supportive role in the males. The cheek pad has no direct bony attachments, but its mass may have a significant effect on facial morphology. The development of the cheek pad is temporally variable and its function remains speculative although the presence of a fully developed flange may be related to behavioral modifications.

Orangutan activity budgets: Monthly variations and the effects of body size, parturition, and sociality

The activity budgets of individual orangutans were investigated at the Kutai Reserve, Indonesia. Activity profiles within and between individuals were compared to examine monthly variations in feeding patterns, potential energetic constraints imposed by large body size and parturition, and the costs of sociality. Animals showed monthly changes in travelling, feeding, and resting patterns. Monthly increases in travelling and feeding were associated with marked reductions in the time spent resting. Inter-individual variations in activity budgets did not exist among animals of the same age-sex class. Activity patterns differed, however, as a function of age and sex. Adult females and subadult males travelled and fed significantly longer than an adult male. Parturition had predictable effects on activity; one female reduced her feeding and travelling immediately following parturition. Adult male orangutan sociality appears to be limited by travel costs. Associations with females forced a male orangutan to travel significantly more compared with periods in which he was solitary. The male did not lose an appreciable amount of time feeding when accompanying a female.

Control of intragroup aggression by a captive male orangutan

AbstractAn adult male orangutan, housed with two adult females, intervened in female‐female aggressive interactions at least seven times over a 4.5‐year period. Five of these seven episodes involved multiple interventions rather than a single act. One series of interventions was directly observed during an ongoing study of spatial relationships, and six other episodes were described in the zoo records. The intervention that was observed directly began with one female displacing the other, after which the male located himself between the two females. He remained nearer the displaced female than he did to the other female. These seven episodes demonstrate the male's mediation and regulation of intragroup aggression. Whereas the opportunities for the control of aggression are limited in the wild, the conditions of captivity likely allowed for the expression of this behavior pattern.

Adult Male Sociality and Reproductive Tactics among Orangutans at Tanjung Puting

During a 4-year period at Tanjung Puting Reserve, Central Indonesian Borneo, adult male orangutans were observed for 2,670 observation hours as focal individuals. Adult male sociality centered around females. Almost the entirety (90%) of adult male participation in social groupings consisted of consortships. If time spent with recent consort partners is included, then adult males spent 95 % of the time that they were in social groups with consorts. Otherwise adult males were quite asocial. Adult males were totally intolerant of each other. Only two brief encounters between lone adult males occurred although avoidance of contact was seen 14 times. Another two encounters between adult males in the presence of females involved much aggression and included a lengthy combat in which the male consort defeated another adult male. Thirty copulations involving adult males were seen; only one copulation was a resisted mating. The other copulations all occurred in consortship. Ten consortships were seen; three involving adult females. While subadult male reproductive tactics predominantly consist of sneak/’rape’, adult male sexual strategy consists primarily of consort/combat tactics. Thus, adult males are interested in attracting and guarding receptive, fertile females. For this reason, wild adult males are relatively selective in choice of consort partner and may reject small proceptive adolescent females.

Sexual selection and adult male orangutan long calls

Long calls given by adult male orangutans ( Pongo pygmaeus) have been hypothesized to mediate interindividual spacing among male orangutans and to attract female orangutans, to high-ranking mates over long distances. To test these two hypotheses I conducted observations of calling behaviour and a series of experimental playbacks of recorded long calls. The findings were consistent with the male-spacing hypothesis but did not support the mate-attraction hypothesis. Experimental playbacks demonstrate that long calls regulate spacing between males through an approach-avoidance system based on dominance relationships: the highest-ranking adult male approaches calls, while lower-ranking, males avoid calls. The results of playbacks also reveal that sexually active females do not move toward long calls, and therefore do not indicate that long calls function in attracting mates. This latter finding suggests that female mate choice may not have been an important selective factor during the evolution of long calls.

Facultative terrestrial hand postures in an orangutan (Pongo pygmaeus) and pongid evolution.

AbstractAn adult male orangutan at the Chicago Zoological Park utilizes various knuckle‐walking hand postures in terrestrial bipedal‐squatting and quadrupedal diagonal‐sequence, diagonal‐couplet gaits. A study was conducted in order to discern the circumstances surrounding the subject's terrestrial locomotor modes. It was found that various locomotor behaviors correlate with specific conditions of the substrate and the subject's motivation. Biomechanical properties of orangutan knuckle‐walking are discussed in terms of their relevance for modelling hominoid phylogeny.

A rare dental abnormality in an adult male Orang‐utan (Pongo pygmaeus): bilateral supernumerary maxillary premolars

A rare dental abnormality in an adult male Orang‐utan (Pongo pygmaeus): bilateral supernumerary maxillary premolars