Golden snub-nosed monkey

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TAXONOMY

Suborder: Haplorrhini
Infraorder: Simiiformes
Superfamily: Hominoidea
Family: Hominidae
Genus: Pongo
Species: P. abelii, P. pygmaeus, P. tapanuliensis
Subspecies: P. p. morio, P. p. pygmaeus, P. p. wurmbii

Other names: orangutan (English, principally American); Orang Utan (German); orangoutan (French); orango (Italian); maias or mawas (Malay); orangután (Spanish); orangutang (Swedish).

MORPHOLOGY

Genetically diverging 1.5 million years ago, phenotypic differences between the two species of orangutan are apparent. Sumatran orangutans are thinner than their Bornean relatives, have paler red coats, longer hair, and longer faces. Adult males have mustaches and prominent cheek pads, called flanges, that are covered with fine, white hair. Both sexes have long beards (Courtenay et al. 1988; Rowe 1996). Bornean orangutans have coarse, long hair that can be orange, brown, or maroon. Infants are born with pink faces but as they age, the pigment changes to dark brown or almost black skin. Males have large, pendulous throat pouches and, compared to the Sumatran species, their cheek pads are markedly larger, covered in short bristly hair (Courtenay et al. 1988; Rowe 1996). Males and females of both species are highly sexually dimorphic, with males weighing, on average, 87 kg (192 lb) and measuring 970 mm (3.18 ft) and females weighing, on average, 37 kg (81.6 lb) and measuring 780 mm (2.56 ft) (Markham & Groves 1990; Rowe 1996).

Orangutans climb using both hands and both feet to hold onto branches as they move horizontally through the rain forest canopy (Rodman 1993). The position of their thumbs and big toes makes it possible to move hand over hand through the trees grasping branches with their feet as well; their fingers and toes act like hooks (Galdikas & Briggs 1999). When they move along the ground, orangutans walk quadrupedally on their fists, not their knuckles as is seen in the other great apes, and they are occasionally seen moving bipedally (Rowe 1996).

Orangutans can live between 50 and 60 years in the wild (Rowe 1996).

RANGE

The two species of orangutan are geographically separated and found only on the islands of Borneo and Sumatra. While the whole of Sumatra is part of Indonesia, the island of Borneo is divided into federal states of Malaysia (Sarawak and Sabah) and provinces of Indonesia (Kalimantan), and is partly comprised of the independent sultanate of Brunei (Kaplan & Rogers 1994). Borneo is the third largest island in the world and orangutans occur at low density in all suitable habitat in eight regions of Borneo: Sabah, Kutai region, central Borneo, Bukit Raya/Bukit Baka, Tanjung Puting, Kendawangan, Gunung Palung, and Gunung Nyuit (Rijksen et al. 1995). Orangutans are mainly found in northwestern Sumatra in the Leuser Ecosystem (formerly Gunung Leuser National Park) and the surrounding area, and may be thinly spread down the west coast of the island (van Schaik et al. 1995; Rijksen & Meijaard 1999). Estimates of the orangutan population on Borneo suggest that there are about 55,000 in the wild, while the Sumatran orangutan is thought to number 7,000 individuals (Singleton et al. 2004). There are about 350 orangutans in captivity in the United States (Rijksen & Meijaard 1999).

Studies on wild orangutans have been on-going for more than 30 years. One of the most important field sites is Tanjung Puting National Park on Borneo, made famous by Biruté Galdikas who, like Jane Goodall (chimpanzees) and Dian Fossey (gorillas), was sponsored by Louis Leakey, to study wild orangutans in the early 1970s. More than just a field study site, Galdikas established a rehabilitation center and tourist program for the area, bringing international attention to the plight of wild orangutans (Rijksen & Meijaard 1999). Bornean orangutans are also studied at Kutai and Sebangau National Parks and Mawas Reserve in Kalimantan and at Kinibatanga in Sabah (Husson pers. comm). The Leuser Ecosystem on Sumatra has several key study sites including Suaq Balimbing, Renun, and Ketambe, though serious habitat loss has compromised research in these forests (Delgado & van Schaik 2000; Husson pers. comm.). Pioneering ecological and behavioral research on wild orangutans at the Ketambe study site in Gunung Leuser was conducted by H.D. Rijksen.

HABITAT

Bornean orangutans live in isolated fragments of the oldest forests on Earth in a total area of 150,000 km² (57,915 mi²) comprised of hilly or mountainous areas as well as lowland swampy areas (Kaplan & Rogers 1994; Rijksen & Meijaard 1999; Rijksen 2001). The two major types of forest on Borneo are peat swamp forest and lowland dipterocarp forest (Rodman 1988). Dipterocarps are members of a family of trees (Dipterocarpaceae) that characterize this area of the world and are highly valued as timber resources (Kaplan & Rogers 1994). Orangutans utilize primary tropical rain forest and old secondary forest at low elevations, though they may also venture into grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes (Galdikas 1988). Rainfall, averaging 4300 mm (14.1 ft) annually, is relatively uniform across the area and is heavy from December through May as well as in September, while June through August is dry. Temperatures range from 18° C (64.4° F) to 37.5° C (99.5° F) (Galdikas 1988; Knott 1998). Orangutans on Borneo occupy all forested habitat except for northern Sarawak and Brunei and the region east of Sungai Barito and south of Sungai Mahakam. They are also thought to be restricted by elevation and are not found in forests at elevations greater than 1000 m (3281 ft) (Husson pers. comm.).

Sumatran orangutans range across a total area of 26,000 km² (10,039 mi²) comprised of wide plateaus and mountainous regions, at elevations up to 1500 m (4921 ft), as well as lowland swamps at sea level (Rijksen & Meijaard 1999). They are found in lower population densities at higher elevations, and lowland dipterocarp, freshwater, and peat swamp forests are of primary importance. Annual rainfall is about 3000 mm (9.84 ft) with the wet seasons ranging from March to June and September to December. Average annual temperature is 29.2° C (84.5° F) but ranges from 17° C (62.6° F) to 34.2° C (93.5° F) and humidity is near 100 % year-round (Rijksen 1978).

ECOLOGY

Orangutans are found in the highest densities in areas which have a mosaic of habitat types that provide high quantities of food throughout the year such as lowland swamp forests, where tree diversity is much higher, than in hilly or mountainous regions (Rodman 1988; Kaplan & Rogers 1994; Russon et al. 2001). Peat swamps support medium-densities of orangutans and they are found in the lowest densities in dipterocarp forests (Husson pers. comm.). They eat a wide variety of plant species but are mainly frugivores 61% of their diet). They have been recorded eating buds, open flowers, young leaves, bark, sap, vines, orchids, reed roots, bird eggs, spider webs, termites, caterpillars, ants, fungi, honey, and other various plant parts (Rijksen 1978; Galdikas 1988). Extreme variability in the abundance of fruit from season to season and year to year is typical of dipterocarp rainforests. Mast fruiting occurs every two to 10 years and is a phenomenon in which large numbers of trees fruit simultaneously despite no seasonal change in temperature or rainfall (Knott 1998). During this time, orangutans engorge themselves with fruit, greatly exceeding their daily caloric intake requirements and putting on additional fat stores. In periods of high fruit abundance, males consume more calories and spend more time feeding per day than females. This propensity to overeat during times of food abundance and efficiency of storing fat reserves may be why captive orangutans often struggle with obesity (Knott 1998). When mast fruiting does not occur during a year, there is still an annual fruit peak. Fruit is widely available during the beginning and end of the rainy season (December and May) and is scarce by the end of the dry season (August) (Galdikas 1988; Knott 1998). Fruit is always preferentially eaten, but when fruits are in short supply, orangutans forage opportunistically and depend more heavily on other plant foods such as bark, pith, leaves, flowers, and insects (Knott 1998). Sumatran orangutans heavily prefer figs over any fruits, especially Ficus species, though figs are largely unavailable to lowland ranging Bornean orangutans (Rijksen 1978; Galdikas 1988).

Orangutans spend more than 95% of their daily activity budgets feeding, resting, and moving between feeding and resting sites (Rodman 1988; 1993). Their daily activity patterns show two peaks, one in the morning and another in late afternoon. After leaving their night nest, orangutans spend two to three hours vigorously feeding in the morning, then rest during the midday hours, travel during the late afternoon, and, in the early evening, prepare their night nests (Rijksen 1978; Galdikas 1988). Day ranges vary between 90 and 3050 m (.056 and 1.90 mi), with an average of 790 m (.491 mi), though males generally travel further than females each day (Galdikas 1988). Day range length is directly proportional to home range size; orangutans with larger home ranges have larger day ranges and those with smaller ones have smaller day ranges (Rodman 1993). In the peat and lowland swamp forests of Borneo, where faunal diversity is great, home ranges for females are between 3.5 and 6 km² (1.35 and 2.32 mi²) (Galdikas 1988). On Sumatra, where orangutans inhabit higher elevations and swamp forests with less diversity, average female home ranges tend to be larger, closer to 8.5 km² (3.28 mi²) Singleton & van Schaik 2001). There is little data on male home ranges because they are likely larger than any study sites, but it is inferred that male home ranges are several times larger than those of females, and as such are neither exclusive nor particularly stable (van Schaik & van Hooff 1996).

Sumatran orangutans are subject to predation by tigers, clouded leopards, hunting dogs, and crocodiles, but tigers constitute the major predatory threat. Clouded leopards are capable of killing Sumatran orangutan adolescents and small adult females, but have not been known to kill adult males (Rijksen 1978). The presence of predators is probably the reason that Sumatran orangutans are rarely seen venturing onto the ground. Bornean orangutans, on the other hand, are not subject to predation by large felids, and are seen more frequently on the ground than the Sumatran species (Rijksen 1978; Galdikas 1988).

SOCIAL ORGANIZATION AND BEHAVIOR

The semi-solitary social organization and behavior of orangutans is highly unusual among the great apes. Adult males and independent adolescents of both sexes range alone while adult females range with their dependent and weaned offspring (te Boekhorst et al. 1990). As subadults, transient males and females may travel in very small groups together, but this does not extend into adulthood. Referred to as resident females, adult females and their infant and juvenile offspring live in discrete home ranges that overlap with other adult females (that may be their mothers or sisters) and within the larger home ranges of an adult male with which they preferentially mate (te Boekhorst et al. 1990; Rodman 1993; Singleton & van Schaik 2002). A resident male is one that has a home range that envelops the ranges of one to several adult females and he is considered the primary breeder for those females within his range. Non-resident males (both subadult and adult) and females range broadly either alone or in groups of a few individuals (Rijksen 1978; te Boekhorst et al. 1990; Mitani et al. 1991; Rodman 1993). The overlap of the home ranges of males and females means that orangutans of both sexes encounter each other while traveling and feeding, and may have brief social interactions (te Boekhorst et al. 1990; Mitani et al. 1991). Adult females that encounter one another can be aggressive, mutually avoid each other, or have seemingly affable relationships (Rijksen 1978; Galdikas 1984). Adult males also have overlap in their ranges and when they meet, encounters between them are usually characterized by agonistic displays. One type of orangutan social group is formed when resident adult males and adult females form a consortship group for a few days, weeks, or even months after copulation. It usually consists of the breeding pair and the adult female’s infant or juvenile offspring (Utami et al. 2002). It is perhaps a better description of orangutan social organization and behavior to say that they are solitary but social rather than semi-solitary (Galdikas 1984).

Dispersal patterns of orangutans revolve, to some degree, around female philopatry. Females settle in home ranges that overlap with their mothers’, though they do not interact with them more frequently than other adult females and there is little to no evidence of female bonding through affiliation, grooming, or agonistic support (Galdikas 1984; van Schaik & van Hooff 1996; Singleton & van Schaik 2002). There is no evidence that females exhibit territoriality. Males disperse over long distances from the home ranges of their mothers and have a seemingly nomadic phase until they can secure a home range, displacing the dominant, resident adult male (Delgado & van Schaik 2000). Male-male competition for mates is quite intense because of constraints on female reproductive potential and wide spatial distribution (Mitani 1989; Rodman 1993). Dominance hierarchies are formed and maintained between adult males that regularly encounter one another and the more dominant males are usually the largest and have the best body condition (van Schaik et al. 2004). Adult males are always dominant over subadult males (Fox 2002).

The social structure of orangutans is related, in some capacity, to their body size and diet. Because of their large size, they have high caloric needs and fruit is not uniformly available, spatially or temporally, in large enough amounts to permit permanent social groups (Delgado & van Schaik 2000). As a result, there is evidence for individual-based fission-fusion grouping where animals associate in parties on a fairly regular basis, but mean party size tends to remain very small (van Schaik 1999). The two types of social parties seen in orangutans are feeding aggregations and travel bands.

Orangutans gather and feed in large fruiting trees with abundant fruit crops (van Schaik & van Hooff 1996). These feeding aggregations include both resident (adult males and females) and non-resident (subadult males and females) orangutans, and individuals arrive and leave independently. Because of the large quantity of fruit available in a single location, competition for resources is decreased and individuals may benefit from social contact (e.g. gain access to mates or socialize infants) (Mitani et al. 1991; van Schaik 1999; van Schaik et al. 2004).

Orangutans also form travel bands, in which individuals coordinate travel between food sources for a few days at a time (Mitani et al. 1991; Delgado & van Schaik 2000). They are seen doing this only when there is a high density of fruit patches, during a mast fruiting for example, and travel bands usually only consist of a few individuals (Sugardjito et al. 1987; van Schaik & van Hooff 1996). Most commonly, these groups are mating consortships, comprised of one adult male and female traveling together and mating (van Schaik et al. 2004).

REPRODUCTION

Most information about reproductive parameters of orangutans comes from captive animals because of the difficulty of assessing reproductive capabilities in the wild (Knott 2001). Among female orangutans, menarche occurs between 5.8 and 11.1 years, and it occurs earlier in larger females with more body fat than in thinner females (Kaplan & Rogers 1994; Knott 2001). Menarche seemingly occurs earlier in captive orangutans than in wild orangutans, though the absence of a sexual swelling may affect estimates in the wild (Knott 2001). There is a period of adolescent infertility, as is seen in the other great apes, but it is unknown how long this lasts among female orangutans. There is some evidence that it persists for one to four years (Galdikas 1995; Knott 2001). The menstrual cycle lasts between 22 and 30 days and menopause has been recorded among captive orangutans at about 48 years old (Kaplan & Rogers 1994; Knott 2001). Gestation is about nine months and wild female orangutans usually give birth for the first time between ages 14 and 15, though they may be younger in captivity (Kaplan & Rogers 1994; Galdikas 1995). Orangutans exhibit the longest interbirth intervals of all great apes with about eight years between births (Galdikas 1995). Though there is no breeding season, female orangutans show significant seasonal differences in ovarian function during periods of food abundance and scarcity and are therefore less likely to conceive during times of ecological stress (Muller & Wrangham 2001). Because of this sensitivity to ecological conditions, females with overlapping home ranges exhibit rough reproductive synchrony (Galdikas 1995).

Male orangutans have a particularly interesting bimodal physical development, referred to as bimaturism or arrested development, which is influenced by the social context in which they live. Sexual maturity occurs between eight and 15 years in males, though they do not exhibit the secondary sexual characteristics or characteristic long-calls of a socially mature adult males (also called flanged males) until they are between 15 and 20 years (Rijksen 1978). Subadult, or unflanged, males (ages eight to 15) have fully descended testicles and are capable of reproducing but remain in a morphological state quite similar to adult females. When the proper social conditions arise, mainly in the absence of a resident male, they begin to develop the characteristic cheek pads, throat pouch, long fur, and behaviors of resident adult males (Rijksen 1978; Schürmann & van Hoof 1986). The shift from unflanged to flanged appearance can occur rapidly, within a few months. Along with the shift in physical appearance comes a shift in mating strategy. Unflanged males do not have a secure territory and are transient, roaming over wide areas and searching for receptive adult females. When they encounter a female in estrus, they force copulation and successfully impregnate her. This rape behavior is different than the strategy of a flanged male that uses long-calls to advertise his location and waits for receptive females to find him (Utami et al. 2002; Setchell 2003). Because females preferentially mate with flanged males, this process of sit-and-wait is effective for fully developed males. Females may also seek out flanged males for protection from sexual harassment by unflanged males (Fox 2002). Both male strategies are successful and frequently observed in and ex situ; in one study, about half of the infants born in one study group were sired by unflanged males (Utami et al. 2002). The mechanisms behind the evolution of this unusual characteristic of orangutan development are not yet fully understood.

PARENTAL CARE

Because of the semi-solitary nature of orangutans, adult males have no contact with infants and therefore no parental investment in the wild. The orangutan mother is the primary care provider and instrument of socialization for her offspring. The strongest, most salient social group among orangutans involves an adult female and her dependent offspring. Because an adult female is likely to have more than one offspring with her (an older adolescent and an infant), older siblings can be very important in socializing infants and juveniles (Munn & Fernandez 1997). From birth to about two years, an infant orangutan is completely dependent on its mother, always being carried during travel, depending on her for food, and sleeping in the same night nest as her (Rijksen 1978). For the first four months, the two never break contact and the infant is carried ventro-ventral. The amount of physical contact wanes over the following months such that by age one the infant is usually only in contact with its mother 25 percent of the time (Munn & Fernandez 1997). By two years of age, climbing and swinging skills are more markedly developed and a common travel form seen is “buddy travel” in which the young orangutan holds the hand of another animal while moving through the canopy (Munn & Fernandez 1997). The juvenile period lasts from about two to five years of age and the young orangutan begins to take short exploratory trips from its mother, but is always in visual contact with her, and play becomes increasingly important (with peers and with its mother) (Rijksen 1978). While a juvenile still sleep in the same nest as its mother, one form of play is to practice building nests, and by the end of this period of development, a juvenile may be sleeping in its own night nest (Rijksen 1978; Munn & Fernandez 1997). This is also the age range in which mothers allow less frequent nursing. By age four, orangutan juveniles are usually weaned, though they may still nurse during periods of stress until they are seven years old (Munn & Fernandez 1997). The adolescent stage starts about age five and lasts until age eight. While adolescents still have frequent contact with their mothers, they actively seek peers and play and travel with peer groups (Rijksen 1978). At this point in development, females are starting to show some sexual behavior, especially towards the resident male, and will begin to establish their own home ranges that overlap with, but do not encompass, their mothers’ ranges (Galdikas 1995). The adolescent male orangutan remains socially immature, though sexually mature, and actively avoids contact with adult males. Once it leaves its mother, it begins its transient stage which lasts until it is able to displace a resident, flanged male, at which point it will develop the flanged appearance and will be considered socially adult.

COMMUNICATION

Orangutan call repertoires (For more information and sonograms, see: M.E. Hardus, A.R. Lameira, I. Singleton, H.C. Morrogh-Bernard, C.D. Knott, M. Ancrenaz, S.S. Utami Atmoko and S.A. Wich, “A description of the orangutan’s vocal and sound repertoire, with a focus on geographic variation.” In. Orangutans: Geographic Variation in Behavioral Ecology and Conservation, ed. by S.A Wich, S.S. Urami Atmoko, T.M. Setia, and C.P. van Schaik. Oxford University Press, 2009.; UniversitÃ¥t Zurich; May 9, 2012)
The most important and easily distinguished vocal communication between orangutans is the long-call. This is only performed by flanged males, lasts for one to two minutes, and can be heard over several kilometers when conditions are right (Mitani 1985; Galdikas & Insley 1988). A flanged male uses this call primarily to alert other males (both subadult and adult) to his presence as well as advertise his presence and location to sexually receptive females (Galdikas & Insley 1988). There is some evidence that the long-call plays an important role in the suppression of development among adolescent and subadult males. When adolescent males hear long-calls, stress hormones are induced and rather than developing secondary sexual characteristics, development is arrested resulting in the unflanged appearance (Delgado & van Schaik 2000). While subadults flee from the sound of long-calls, sexually receptive females use it as a tracking device for flanged males and respond accordingly (Delgado & van Schaik 2000). Long-calls are made spontaneously by males, unlike the other characteristic call of adult males which is used under very specific conditions. The fast-call is elicited post-contact or post-conflict. For example, after hearing a long-call, crashing branches or trees (circumstantial evidence of another male in the vicinity), or seeing another male fleeing, a flanged male will respond with a fast call (Mitani 1985; Galdikas & Insley 1988). There is little information on other orangutan vocalizations; because of their semi-solitary lifestyle, vocal communication may not as important as it is for other apes.

Like the other great apes, orangutans are highly intelligent and closely related to humans and as such they have been the focus of language acquisition studies as researchers try to understand the origins of human language. Fewer attempts have been made to teach orangutans American Sign Language than chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). An orangutan named Chantek learned about 140 signs and was able to use them spontaneously, though most of his interest remained on signing about foods (Miles 1990).

SPECIAL NOTES

Sumatran orangutans of all ages and sex classes use and manufacture tools. While tool use was first seen and studied among captive orangutans, subsequent field work at Suaq Balimbing, Sumatra revealed that wild orangutans are also quite deft at using and making tools, but the behavior is rarely seen among Bornean orangutans (Commitante et al. 2003). In the wild, orangutans are seen using found objects as tools: leaves as “toilet paper,” leafy branches as flyswatters, large leaves as umbrellas, and branches used in displays (Fox et al. 1999). They also manufacture tools: modifying sticks for collection of insects and to pry open large fruit and seed pods, and using stacks of leaves to hold spiny fruit as they open it (Fox et al. 1999). Captive orangutans are also capable of manufacturing tools for a variety of uses and situations: connecting short sticks to make one long stick to reach desired object, stacking boxes to make a ladder, using sticks to dig holes, making swings from ropes, and containing water by using objects as cups (Lethmate 1982). In some instances, orangutans score higher on tool-using tests in captivity than do chimpanzees by, for example, using one tool to make another. (Lethmate 1982).

INTERNATIONAL STATUS

CITES: Appendix I
IUCN Red List: P. abelii: CR; P. pygmaeus: EN
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The total population of Pongo pygmaeus is estimated to be no more than 15,000 individuals, though the inaccessibility of much of their range, poor visibility in dense forests, and the cryptic nature of the animals makes it difficult to survey with precision (Sugardjito 1995; Sodaro 1997; Rijksen & Meijaard 1999).

The same difficulties assessing the population size that plague researchers on Bornean orangutans apply to the Sumatran orangutan as well. On Sumatra, the orangutan population is approximately 12,000 individuals, though this is the upper limit of the estimate (Rijksen & Meijaard 1999). In some areas, the rate of loss during the 1990s was about 1,000 orangutans per year leaving some estimates of the Sumatran population between 3,500 and 5,000 individuals (Delgado & van Schaik 2000; van Schaik et al. 2001; Wich et al. 2003).

The most serious threat to orangutan viability is the unsustainable practice of timber extraction in Indonesia and Malaysia. Habitat destruction and the subsequent degradation, either from commercial timber harvesting or conversion of land to agriculture poses a very serious threat to these arboreal apes. Moreover, the illegal pet trade is booming in Southeast Asia and infant orangutans are very popular pets (Sodaro 1997). The low densities, small population size, and increasing pressure on their habitat coupled with certain factors of orangutan behavioral ecology including diet, low reproductive rates, extensive period of development, and the longest interbirth interval of any great ape, make the orangutan extremely vulnerable to extinction in the near future if threats are not minimized (Morrogh-Bernard et al. 2003).

CONSERVATION THREATS & POTENTIAL SOLUTIONS

Threat: Human-Induced Habitat Loss and Degradation

The single largest threat to orangutan populations is the ongoing loss of habitat (Sugardjito & van Schaik 1993; Sugardjito 1995; Rijksen & Meijaard 1999). During the second half of the twentieth century, more than half of the forest cover on Borneo disappeared and more than 80% of the orangutan habitat was destroyed. Poorly managed timber extraction coupled with conversion of forest to agricultural land (both subsistence and commercial) continue to threaten these apes (Rijksen 2001). Sumatran orangutans did not fare much better in the twentieth century, but because of the nature of their habitat (steep, mountainous terrain) human encroachment and agricultural opportunities have been limited. Thus while their numbers are lower and the area of occupancy smaller than their Bornean counterparts, Sumatran orangutans live in less degraded habitats (van Schaik 2000; Rijksen 2001).

Because all orangutans are exclusively reliant on trees for their existence, this makes the destruction of forests devastating to every aspect of their lives (Sugardjito 1995). Though fruiting trees are not generally coveted timber trees, the collateral damage from the removal of dipterocarps negatively impacts the surrounding habitat for other plant species and fruiting trees and vines are damaged (Sugardjito 1995; van Schaik et al. 2001). Moreover, because of the patchy distribution of orangutan food supply (fruiting trees dot the landscape rather than dominate it), the loss of any of these ecologically important plant species makes it difficult to forage efficiently and intraspecies competition may heighten (Sugardjito 1995; Felton et al. 2003). Another factor of tropical timber harvesting that threatens orangutans, especially in Borneo, is extraction of trees in peat swamp forests. These forests support the highest observed population densities of orangutans in any forest type as well as support commercially valuable timber (Russon et al. 2001; Felton et al. 2003; Morrogh-Bernard et al. 2003). As trees are extracted, peat swamp forests lose their value to orangutans and these pockets of dense orangutan populations decline or are eliminated (Felton 2003). Displaced orangutans do not generally survive and succumb to disease, hunting, or capture for trade (Delgado & van Schaik 2000; van Schaik et al. 2001).

Compounding the problem of commercial timber harvest is illegal logging. Rather than following a mandated 30- to 40-year rest period before felling more trees in an area, logging generally continues until all of the commercially valuable timber has been extracted (van Schaik et al. 2001). The natural processes of regeneration do not occur and the booming human population can take advantage of the cleared land, moving in and planting agricultural crops (Delgado & van Schaik 2000). Illegal logging may also be responsible for higher levels of collateral damage as well. Unskilled laborers working unsupervised cause unnecessary damage to the surrounding ecosystem (Felton et al. 2003). Roads built by logging companies and access via rivers together with the complete lack of law enforcement make formerly isolated patches of forest vulnerable to exploitation by timber poachers and commercial agriculturalists (van Schaik et al. 2001). Oil palm plantations are an increasingly serious threat to orangutan habitat as land is completely converted from recovering logged forest to monoculture plantations (Robertson & van Schaik 2001). Weak compliance with regulations, weak law enforcement, and weak legal environment all contribute to illegal timber harvesting and agriculture (Robertson & van Schaik 2001).

Potential Solutions

If orangutan populations are to recover, habitat destruction must be halted and sufficient protection must be extended to them (Yeager 1999; Robertson & van Schaik 2001; Felton et al. 2003). Even hand-logging, which has been considered less disruptive than mechanized logging, does significant damage to orangutan habitat because of the haphazard practices implemented by illegal logging crews (Felton et al. 2003). Adequate funding is necessary to ensure that the laws and restrictions against timber extraction in national parks and reserves are enforced (Robertson & van Schaik 2001). Some of this funding could come from logging companies themselves. Each time part of their concession is illegally harvested, they lose potential profit to poachers therefore the companies have some incentive to protect the land. Revoking licenses of concessionaires or fining logging companies for not adhering to approved logging practices in designated areas could decrease impact while also increasing revenue for conservation. Saw mills could also be subject to review, requiring permits to operate and implementing fines for processing illegal timber.

Other options for enforcement are community-based protection initiatives in which local communities living around national parks and protected areas are responsible for guarding the forests from timber poachers. Coupled with education programs, these orangutan protection units could be potential income earning opportunities for local people as well as create a sense of pride for endemic natural resources (Rosen & Byers 2002). These community-based programs will only be successful, though, if corruption at higher levels can be abated (Robertson & van Schaik 2001). Alternative income opportunities could also be developed in buffer areas surrounding national parks and preserves and would alleviate some pressure on the natural resources within parks (Yeager 1999).

Though enforcing regulations in legally protected areas is challenging, existing protected areas need to be expanded and new areas must be created if orangutan populations are to remain viable. Currently, no more than 16% of the range of Bornean orangutans is protected, while Sumatran orangutans are protected in 73% of their range (though their range is much smaller than that of their Bornean relatives) (Rijksen 2001). Where logging has occurred and forests are fragmented, measures must be taken to create corridors and allow gene flow between geographically separated populations. Money from international loans can be used to implement these projects and local people can become involved in application of these principles. Because of the rampant corruption, though, these loans must be linked to tangible conservation accomplishments subject to third-party review (Robertson & van Schaik 2001).

Certifying lumber that has been extracted properly and is “orangutan-friendly” is another option to decrease impact on habitat. Timber companies can sell this lumber for a higher price and increase their revenues if the certified wood is designated as such. Encouraging users of tropical hardwood and palm oil to decrease consumption or only purchase those products that have been certified may also decrease demand for “unfriendly” products on the global market and decrease their value.

Translocating displaced orangutans from logged forests to less disturbed habitats may decrease mortality associated with severely degraded habitats (Wich et al. 2003). If patches are too small or too severely logged, occupant orangutans could be moved to more appropriate areas and supplemented with food, if necessary, until isolated fragments are connected with forest corridors (Wich et al. 2003). Translocation is considered an emergency measure, though, and funding should be directed toward preventing the causes of displacement (Yeager 1999).

Threat: Invasive Alien Species

Ape-based ecotourism is an important source of revenue for orangutan conservation organizations. These programs revolve around rescue and rehabilitation centers that care for and sometimes release orangutans that have been seized from illegal sources (Sugardjito & van Schaik 1993; Delgado & van Schaik 2000). As a result, orangutans come into frequent close contact with tourists, caregivers, guards, and guides and potentially are exposed to zoonotic diseases. Because of their phylogenetic closeness to humans, all great apes are subject to some human diseases (Woodford et al. 2002). Orangutans that come into close contact with humans through ecotourism and rehabilitation centers are exposed to a myriad of pathogens that may decrease their viability or, even worse, could have catastrophic consequences if the infectious disease is transmitted to an entire population. Because wild orangutan populations are so small and fragmented to begin with, any added stress such as pathogens or parasites could be cataclysmic (woodford et al. 2002). Potential risks include aerosol/inhalation transmission, fecal/oral transmission, and indirect routes of transmission such as intermediate hosts (eg. insects). Diseases that have been known to affect great apes include paralytic poliomyelitis, pneumonia, measles, and tuberculosis and wild orangutans have had diagnoses including hepatitis A,B,C, D, and E, leptospirosis, cholera, malaria, HIV, and tuberculosis (Smits et al. 1995; Kilbourn et al. 1998; Woodford et al. 2002).

Potential Solutions

Proper protocol should be followed to minimize the possibility of disease transmission to habituated orangutans in rehabilitation centers, especially those that come into frequent, close contact with tourists. Health checks (simple questionnaires) for tourists should be prerequisite for any visit to orangutan centers. Proper distance should be kept and good sanitation should be practiced before and after coming in contact with these apes. It is also important for personnel of orangutan centers to have current vaccinations and practice good hygiene in order to minimize disease transmission on a daily basis (Woodford et al. 2002).

Threat: Harvesting (hunting/gathering)

Another significant threat to orangutan survival is hunting as meat and subsequent capture of wild orangutans for sale into the pet trade (Rijksen 2001). This practice is closely tied to swidden agriculture; as local people burn fires to clear forested areas, orangutans within those areas flee from the conflagration and are captured for meat or sale (Rijksen 2001).

It is also directly linked to forest destruction because as timber harvests, both legal and illegal, increase and food sources become more intermittent, orangutans venture out of the forests into surrounding plantations and fields, stealing food and acting as agricultural pests. When this occurs, local people have little tolerance for the apes. As conflicts arise, orangutans are shot or poisoned and surviving infants and juveniles are taken and sold (Rijksen 2001). It is estimated that about two orangutans per week are smuggled off of Borneo and are taken to Singapore for distribution (Rosen & Byers 2002). Many illegal pet orangutans are seized en route to or in Taiwan, a principal destination for illegally trafficked wild orangutans. A popular Taiwanese television show featuring an orangutan as an ideal pet and companion is likely responsible for the popular idea of orangutans as pets (Lee et al. 1993).

Orangutans are also hunted for their meat in some areas, especially in the interior of Borneo. Because of their deliberate and slow locomotion, orangutans are easy targets for hunters even from a distance (Sugardjito 1995). Though the indigenous people in much of this area are Muslim and therefore have religious taboos against eating any meat, including orangutan, the ape population is dwindling because even the slightest hunting pressure on areas of precariously low population densities has significant effects (Sugardjito 1995). Moreover, adult females are usually found in the highest population densities of any demographic and are therefore more vulnerable to poaching. In addition, they usually travel with at least one dependent offspring, probably two. If the adult female is killed for food, her offspring are seized and sold as pets (Yeager 1999).

Potential Solutions

A long-time solution to the pet trade has been rescue and rehabilitation programs for orangutans seized from poachers and pet dealers, coupled with law enforcement and strict regulation to prevent the illegal trade (Delgado & van Schaik 2000). The main rehabilitation centers include Sepilok in Sabah, Semonggok in Sarawak, Wanariset in East Kalimantan, and Bohorok on Sumatra (Yeager 1999). Though it is generally acknowledged that rehabilitation is a necessary, temporary measure, these centers and policies have been met with some criticism about their mediocre success of preventing poaching and illegal trade while subjecting orphaned orangutans to questionable social and ecological environments (Smits et al. 1995; Rijksen 2001). This practice has become commercialized and tourists can pay to visit rehabilitation centers for an up-close encounter with orangutans. More recently, there has been a shift in which orangutans are involved in ecotourism ventures. Rather than viewing and interacting with all orangutans, tourists are introduced to orangutans that are not candidates for reintroduction due to chronic illness or permanent disability (Rosen & Byers 2001). The focus in the centers should remain on rehabilitation — returning apes to a proper state for feral existence. In the broader context, more financial and administrative effort should be focused on preventing poaching and habitat conservation (Rijksen 2001). Funding for education of local communities should be increased if orangutan poaching is to stop in and around national parks. Reintroduction of rehabilitated orangutans should therefore not garner the same amount of funding and effort as reducing the source of orangutans in need of rehabilitation (Yeager 1999).

Protocol has been developed to meet the needs of orangutans in rescue and rehabilitation centers. Measures to ensure the health of orangutans in rehabilitation programs have been put in place and include a quarantine period for newcomers, routine healthcare and screenings while in captivity, and complete diagnostic testing before reintroducing rehabilitated animals to conditions where they have the opportunity to interact with wild orangutans (Rosen & Byers 2001).

Policies regarding diet, social grouping, amount of interaction with caregivers and other humans, as well as preparedness training (social and ecological) have all been implemented. Captive breeding is also discouraged and is avoided by management techniques. Very specific recommendations for the reintroduction of captive orangutans have also been outlined and include reintroduction into suitable environment with adequate protection, area free of wild orangutans (to reduce spread of non-endemic diseases to already precarious populations), geographic isolation from other populations to decrease risk of disease transmission, and follow-up research to monitor the progress of reintroduced animals (Rosen & Byers 2001).

Reintroduced orangutans usually spend some amount of time remaining in the vicinity of their release cage (days to weeks) and very young orangutans have difficulty moving about in trees, instead staying on the ground, huddled with their conspecifics (Grundmann et al. 2000). Other skills that have been noticeably absent in newly released orangutans also include nest building and fruit acquisition and processing. One way to counter this lack of appropriate skills is to pair the youngest orangutans with older, more knowledgeable orangutans and allow the natural transfer of knowledge that would occur in a normal orangutan family (Grundmann et al. 2000). Obviously supplementing newly reintroduced orangutans is essential to their survival, but it is also important to closely monitor their progress and possibly remove them if attempts to assimilate are unsuccessful.

Threat: Persecution

Orangutans are subject to persecution because in some areas they become pests. In altered ecosystems, orangutans compete with people for fruit where it is scarce (van Schaik et al. 2001). Moreover, as food sources become increasingly sporadic in severely degraded habitats, orangutans are forced to venture into surrounding agricultural areas and steal food. They are often shot or poisoned if they are caught. (Rijksen 2001).

Potential Solutions

Shifting the attitudes of local people is essential to conserving orangutans. Increasing tolerance of these apes is necessary if persecution is to end, especially because it is likely to continue as more habitat is destroyed and orangutans are forced to forage in plantations and fields. Local people could receive payment for crop damage or losses caused by orangutans or they could be advised on which crops are less attractive to orangutan raiders, such as sugarcane (Rosen & Byers 2001).

Threat: Natural Disasters

Climate change has played a significant role in the loss of Bornean orangutans and could have significant effects on both species in the future. Widespread drought following the El Niño/Southern Oscillation of 1997-98 led to the largest fire disaster ever observed and resulted in the burning of millions of acres. Though normally not vulnerable to fires even during drought, tropical forests that are severely logged are at high risk for destruction by wildfires (Siegert et al. 2001). The use of fire is widely employed as a tool to clear land for commercial and subsistence agriculture as well as hunting in some areas of Indonesia. During periods of severe drought brought on by El Niño, the logged forests were particularly sensitive to fire activity and many fires started by local people resulted in uncontrollable forest fires that burned over 12 million acres and killed thousands of orangutans (Delgado & van Schaik 2000; Siegert et al. 2001). In fact, it is estimated that 33 % of the orangutan population on Borneo was lost during the massive fires in the 1990s (Rijksen & Meijaard 1999).

Potential Solutions

Though there is no solution to drought or its underlying causes, some important management techniques can be implemented to decrease the likelihood of another El Niño event decimating the orangutan population. As discussed above, decreasing logging activity in prime orangutan habitat is necessary and would decrease the chance of fire affecting the forests. Furthermore, giving incentives to corporations and local people to change their land clearing techniques would reduce the opportunity for fires to get out of control. Another management option is to plant fire resistant trees as buffers surrounding orangutan habitats (Rosen & Byers 2002).

Threat: Intrinsic Factors

There are some characteristics that make orangutans particularly susceptible to environmental change and lead to more rapid disappearance of both species. Orangutans are poor dispersers and where their habitats are severely disturbed or fragmented and they travel with great reluctance across open areas (Delgado & van Schaik 2000). This creates stressful situations for orangutans, which, in all likelihood, are already experiencing high stress levels because of the lack of foraging opportunities in their degraded home ranges (van Schaik et al. 2001). Furthermore, female orangutans that have limited access to high quality foods such as fruit (caused by seasonal changes or habitat destruction) have lower reproductive output (Knott 1998; Yeager 1999). Because of the extensive period of development and already long interbirth intervals, any decrease in reproductive capabilities caused by ecological factors may cause negative growth in the overall population of orangutans. This would be disastrous for animals that are already living precariously.

Potential Solutions

Habitat loss and destruction are at the root of the orangutan conservation crisis. Ecological factors are intrinsically linked to behavioral characteristics in all primate species, but in the instance of the orangutan, changing the ecological environment has quite far reaching effects. Halting habitat destruction will mitigate the demographic effects that make the orangutan populations in Borneo and Sumatra so unstable.

Threat: Human Disturbance

Economic and political instability in the region has been a contributing factor to habitat loss in recent years. The Asian financial crisis had serious effects on Indonesia’s economy and violent demonstrations led to the resignation of long-term president Suharto (Robertson & van Schaik 2001). The fall of this regime translated to political upheaval and mass anarchy eventually leading to increases in illegal logging and orangutan poaching (Delgado & van Schaik 2000; Robertson & van Schaik 2001). On Sumatra, armed conflict involving separatists added to the chaotic atmosphere and lawlessness there and contributed to existing problems of illegal logging and poaching (Robertson & van Schaik 2001).

Potential Solutions

Corruption has long been rampant in Indonesia’s government and while democratic elections have ensued since Suharto was overthrown, the problem seems to remain common (Robertson & van Schaik 2001). The connection between conservation and political will cannot be underestimated and human rights groups for democracy as well as Indonesian NGOs must be willing to further the cause on Borneo and Sumatra. Transitioning from a corrupt, nepotistic government is certainly no easy task and one that will take efforts from multiple organizations and concerned individuals.

REFERENCES

Commitante R, Husson S, Morrogh-Bernard H, Chivers DJ. 2003. Where the wild things are not- the plight of the wild orangutan. Biologist 50(2): 75-80.

Courtenay J, Groves C, Andrews P. 1988. Inter- or intra-island variation? An assessment of the differences between Bornean and Sumatran orang-utans. In: Schwartz JH, editor. Orang-utan biology. p 19-29.

Delgado RA Jr., van Schaik CP. 2000. The behavioral ecology and conservation of the orangutan (Pongo pygmaeus): a tale of two islands. Evol Anthro 9(1): 201-18.

Felton AM, Engrström LM, Felton A, Knott CD. 2003. Orangutan population density, forest structure and fruit availability in hand-logged and unlogged peat swamp forests in West Kalimantan, Indonesia. Biol Cons 114: 91-101.

Fox EA. 2002. Female tactics to reduce sexual harassment in the Sumatran orangutan (Pongo pygmaeus abelii). Behav Ecol Sociobiol 52: 93-101.

Fox EA, Sitompul AF, van Schaik CP. 1999. Intelligent tool use in wild Sumatran orangutans. In: Parker ST, Mitchell RW, Miles HL, editors. The mentalities of gorillas and orangutans: comparative perspectives. Cambridge (England): Cambridge Univ Pr. p 99-116.

Galdikas BMF. 1984. Adult female sociality among wild orangutans at Tanjung Puting Reserve. In: Small MF, editor. Female primates: studies by women primatologists. New York: Alan R. Liss. p 217-35.

Galdikas BMF. 1988. Orangutan diet, range, and activity at Tanjung Puting, Central Borneo. Int J Primatol 9(1): 1-35.

Galdikas BMF. 1995. Social and reproductive behavior of wild adolescent female orangutans. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Pr. p 163-82.

Galdikas BMF, Briggs N. 1999. Orangutan odyssey. New York: Harry N. Abrams. 144 p.

Galdikas BMF, Insley SJ. 1988. The fast call of the adult male orangutan. J Mammal 69(2): 371-82.

Groves C. 2001. Primate taxonomy. Smithsonian Inst Pr. 350 p.

Grundmann E, Lestel D, Boestani AN, Bomsel M-C. 2000. Learning to survive in the forest: what every orangutan should know. In: The apes: challenges for the 21st century. Conference proceedings; 2000 May 10-13; Brookfield, IL. Chicago: Chicago Zoo Soc. p 300-4.

Kaplan G, Rogers LJ. 1994. Orang-utans in Borneo. Armidale (Australia): Univ New England. 196 p.

Kilbourn AM, Karesh WB, Bosi EJ, Cook RA, Andau M, Woolfe ND. 1998. Disease evaluation of free-ranging orangutans (Pongo pygmaeus pygmaeus) in Sabah, Malaysia. In: Baer CK, editor. Proceedings American Association of Zoo Veterinarians and American Association of Wildlife Veterinarians Joint Conference; 1998 Oct 17-22; Omaha, NE. p 417-21.

Knott CD. 1998. Changes in orangutan caloric intake, energy balance, and ketones in response to fluctuating fruit availability. Int J Primatol 19(6): 1061-79.

Knott C. 2001. Female reproductive ecology of the apes: implications for human evolution. In: Ellison PT, editor. Reproductive ecology and human evolution. New York: Aldine de Gruyter. p 429-63.

Lee LL, Phipps M, Chen PC. 1993. The orangutan in Taiwan. In: Tilson R, Traylor-Holzer K, Seal U, editors. Orangutan population and habitat viability analysis workshop: briefing book; 1993 Jan 18-20; Medan, North Sumatra, Indonesia. Apple Valley (MN): IUCN/SSC Captive Breeding Specialist Group. p 105-11.

Lethmate J. 1982. Tool-using skills of orang-utans. J Hum Evol 11: 49-64.

Markham RM, Groves CP. Brief communication: weights of wild orang utans. Am J Phys Anthro 81: 1-3.

Miles HLW. 1990. The cognitive foundations for reference in a signing orangutan. In: Parker ST, Gibson KR, editors. “Language” and intelligence in monkeys and apes. Cambridge (England): Cambridge Univ Pr. p 511-39.

Mitani JC. 1985. Sexual selection and adult male orangutan long calls. Anim Behav 33: 272-83.

Mitani JC. 1989. Orangutan activity budgets: monthly variations and the effects of body size, parturition, and sociality. Am J Primatol 18: 87-100.

Mitani JC, Grether GF, Rodman PS, Priatna D. 1991. Associations among wild orang-utans: sociality, passive aggregations or chance? Anim Behav 42(1): 33-46.

Morrogh-Bernard H, Husson S, Page SE, Rieley JO. 2003. Population status of the Bornean orang-utan (Pongo pygmaeus) in the Sebangau peat swamp forest, Central Kalimantan, Indonesia. Biol Cons 110(1): 141-52.

Muller MN, Wrangham RW. 2001. Reproductive ecology of male hominoids. In: Ellison PT, editor. Reproductive ecology and human evolution. New York: Aldine de Gruyter. p 397- 427.

Munn C, Fernandez M. 1997. Infant development. In: Sodara C, editor. Orangutan species survival plan husbandry manual. Chicago (IL): Orangutan Species Survival Plan. p 59-66.

Rijksen HD. 1978. A field study on Sumatran orang utans (Pongo pygmaeus abelii Lesson 1827): ecology, behaviour and conservation. Wageningen (The Netherlands): H. Veenman Zonen BV. 420 p.

Rijksen HD. 1993. How to save the mysterious “man of the rain forest”?. In: Tilson R, Traylor-Holzer K, Seal U, editors. Orangutan population and habitat viability analysis workshop: briefing book; 1993 Jan 18-20; Medan, North Sumatra, Indonesia. Apple Valley (MN): IUCN/SSC Captive Breeding Specialist Group. p 317-41.

Rijksen HD. 1995. The neglected ape? NATO and the imminent extinction of our close relative. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Pr. p 13-21.

Rijksen HD. 2001. The orangutan and the conservation battle in Indonesia. In: Beck BB, Stoinski TS, Hutchins M, Maple TL, Norton B, Rowan A, Stevens EF, Arluke A, editors. Great apes & humans: the ethics of coexistence. Washington DC: Smithsonian Inst Pr. p 57-70.

Rijksen HD, Meijaard E. 1999. Our vanishing relative: the status of wild orang-utans at the close of the twentieth century. Dordrecht (The Netherlands): Kluwer Acad. 480 p.

Rijksen HD, Ramono W, Sugardjito J, Lelana A, Leighton M, Karesh W, Shapiro G, Seal US, Traylor-Holzer K, Tilson R. 1995. Estimates of orangutan distribution and status in Borneo. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Pr. p 117-22.

Robertson JMY, van Schaik CP. 2001. Causal factors underlying the dramatic decline of the Sumatran orang-utan. Oryx 35(1): 26-38.

Rodman PS. 1988. Diversity and consistency in ecology and behavior. In: Schwartz JH, editor. Orang-utan biology. p 31-51.

Rodman PS. 1993. Diversity and consistency in ecology and behavior. In: Tilson R, Traylor-Holzer K, Seal U, editors. Orangutan population and habitat viability analysis workshop: briefing book; 1993 Jan 18-20; Medan, North Sumatra, Indonesia. Apple Valley (MN): IUCN/SSC Captive Breeding Specialist Group. p 31-51.

Rosen N, Byers O, editors. 2002. Orangutan conservation and reintroduction workshop: final report; 2002 June 19-22; Palangka Raya, Kalimantan, Indonesia. Apple Valley (MN): IUCN/SSC Captive Breeding Specialist Group. 138 p.

Rowe N. 1996. The pictorial guide to the living primates. East Hampton (NY): Pogonias Pr. 263 p.

Russon AE, Erman A, Dennis R. 2001. The population and distribution of orangutans (Pongo pygmaeus pygmaeus) in and around the Danau Sentarum Wildlife Reserve, West Kalimantan, Indonesia. Biol Cons 97(1): 21-8.

Schürmann CL, van Hooff JARAM. 1986. Reproductive strategies of the orang-utan: new data and a reconsideration of existing sociosexual models. Int J Primatol 7(3): 265-87.

Setchell JM. 2003. The evolution of alternative reproductive morphs in male primates. In: Jones CB, editor. Sexual selection and reproductive competition in primates: new perspectives and directions. Volume 3, Special topics in primatology. Norman (OK): American Society of Primatologists. p 410-35.

Siegert F, Ruecker G, Hinrichs A, Hoffmann AA. Increased damage from fires in logged forests during droughts caused by El Niño. Nature 414(6862): 437-40.

Singleton I, van Schaik CP. 2001. Orangutan home range size and its determinants in a Sumatran swamp forest. Int J Primatol 22(6): 877-911.

Singleton I, van Schaik CP. 2002. The social organisation of a population of Sumatran orang-utans. Folia Primatol 73: 1-20.

Singleton I, Wich S, Husson S, Stephens S, Utami Atmoko S, Leighton M, Rosen N, Traylor-Holzer K, Lacy R, Byers O, editors. 2004. Orangutan population and habitat viability assessment: final report. Apple Valley (MN): IUCN/SSC Cons Breed Spec Group. 257 p.

Smits WTM, Heriyanto, Ramono WS. 1995. A new method for rehabilitation of orangutans in Indonesia. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Pr. p 69-77.

Sodaro V. 1997. Distribution, conservation status, and causes of population decline. In: Sodara C, editor. Orangutan species survival plan husbandry manual. Chicago (IL): Orangutan Species Survival Plan. p 12-4.

Sugardjito J. 1995. Conservation of orangutans: threats and prospects. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Pr. p 45-9.

Sugardjito J, te Boekhorst IJA, van Hooff JARAM. 1987. Ecological constraints on the grouping of wild orang-utans (Pongo pygmaeus) in the Gunung Leuser National Park, Sumatra, Indonesia. Int J Primatol 8(1): 17-41.

Sugardjito J, van Schaik CP. 1993. Orangutans: current population status, threats, and conservation measures. In: Tilson R, Traylor-Holzer K, Seal U, editors. Orangutan population and habitat viability analysis workshop: briefing book; 1993 Jan 18-20; Medan, North Sumatra, Indonesia. Apple Valley (MN): IUCN/SSC Captive Breeding Specialist Group. p 142-52.

te Boekhorst IJA, Schürmann CL, Sugardjito J. 1990. Residential status and seasonal movements of wild orang-utans in the Gunung Leuser Reserve (Sumatera, Indonesia). Anim Behav 39(6): 1098-1109.

Utami SS, Goossens B, Bruford MW, de Ruiter JR, van Hooff JARAM. 2002. Male bimaturism and reproductive success in Sumatran orang-utans. Behav Ecol 13(5): 643-52.

van Schaik CP. 1999. The socioecology of fission-fusion sociality in orangutans. Primates 40(1): 69-86.

van Schaik CP, Monk KA, Robertson JMY. 2001. Dramatic decline in orang-utan numbers in the Leuser Ecosystem, Northern Sumatra. Oryx 35(1): 14-25.

van Schaik CP, Poniran S, Utami S, Griffiths M, Djojosudharmo S, Nitra Setia T, Sugardjito J, Rijksen HD, Seal US, Fast T, et al. 1995. Estimates of orangutan distribution and status in Sumatra. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Pr. p 109-16.

van Schaik CP, Preuschoft S, Watts DP. 2004. Great ape social systems. In: Russon AE, Begun DR, editors. The evolution of thought: evolutionary origins of great ape intelligence. Cambridge (England): Cambridge Univ Pr. p 190-209.

van Schaik, CP, van Hooff JARAM. 1996. Toward an understanding of the orangutan’s social system. In: McGrew WC, Marchant LF, Nishida T, editors. Great ape societies. Cambridge (England): Cambridge Univ Pr. p 3-15.

Wich SA, Singleton I, Utami-Atmoko SS, Geurts ML, Rijksen HD, van Schaik CP. 2003. The status of the Sumatran orang-utan Pongo abelii: an update. Oryx 37(1): 49-54.

Woodford MH, Butynski TM, Karesh WB. 2002. Habituating the great apes: the disease risks. Oryx 36(2): 153-60.

Yeager C, editor. 1999. Orangutan Action Plan. Jakarta (Indonesia): WWF-Indonesia. 34 p.

IMAGES

Rhinopithecus roxellana
Photo: A. S. Clarke
Rhinopithecus roxellana
Photo: A. S. Clarke
Rhinopithecus roxellana
Photo: A. S. Clarke
Rhinopithecus roxellana
Photo: A. S. Clarke
Rhinopithecus roxellana
Photo: A. S. Clarke
Rhinopithecus roxellana
Photo: Anne Savage
Rhinopithecus roxellana
Photo: Anne Savage
Rhinopithecus roxellana
Photo: Anne Savage
Rhinopithecus roxellana
Photo: Cyril Grueter
Rhinopithecus roxellana
Photo: Cyril Grueter
Rhinopithecus roxellana
Photo: Cyril Grueter
Rhinopithecus roxellana
Photo: Frans de Waal
Rhinopithecus roxellana
Photo: Nancy Staley
Rhinopithecus roxellana
Photo: R. Garrison
Rhinopithecus roxellana
Photo: Yan Kanghui
Rhinopithecus roxellana
Photo: Yan Kanghui
Rhinopithecus roxellana
Photo: Yan Kanghui
Rhinopithecus roxellana
Photo: Yan Kanghui
Rhinopithecus roxellana
Photo: Yan Kanghui

 

Cite this page as: Cawthon Lang KA. 2005 June 13. Primate Factsheets: Orangutan (Pongo) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/orangutan/taxon>. Authored June 13, 2005 by Kristina Cawthon Lang. Reviewed by Simon Husson. Updated June 13, 2005.

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