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Orangutan
 

The orangutan is the largest tree-living animal in the world. Males stand approximately 4½ ft. and weigh approximately 90 kg (200 lbs.). Females stand approximately 3½ ft and weigh about 50kg (110 lbs.). The body is covered with a dark rufous or reddish brown, rather thin, shaggy coat. The arms are 1½ times longer than the legs and large adult males can have an armspan as long as 8 feet. The shoulder and hip joints are extremely supple, allowing each limb to move easily in any direction. The feet and hands are almost identical. The thumbs are comparatively much shorter than those of other ape species, as longer thumbs would inhibit swinging through the trees. The feet are also prehensile to aid in grasping. The Sumatran orangutans tend to be lighter in color and have longer thicker hair than the Borneans. The most striking difference between the two are the faces of the adult males. The Bornean male adults develop large cheek flanges as they sexually mature. These grow outward and forward from the skull, giving the face a concave shape. The Sumatran males develop cheek flanges that grow sideways rather than forward, giving the face a more flattened look. The Sumatrans also tend to grow longer beards and moustaches than the Borneans.

Orangutan Facts

Range

Orangutans are currently found on the island of Borneo, which is divided between the nations of Malaysia and Indonesia, and on the northern tip of the Indonesian island of Sumatra. Historically orangutans ranged throughout much of Southeast Asia. The two types of orangutan have been isolated from each other for over one million years, with no route of gene flow between the two. This prompted scientists to re-classify them as two distinct species, Pongo pygmaeus (Bornean) and Pongo abelii (Sumatran).

Habitat

Orangutans inhabit tropical rainforest as well as peat swamp forest. They primarily utilize the middle canopy. Large tracts of mature forests are needed to sustain this species. It is estimated that suitable orangutan habitat in Malaysia and Sumatra has declined by more than 80% in the last two decades.

Diet

There are more than 300 different food items identified in their diet, and most of them are fruits. Some of the fruits that orangutans consume include jackfruit, durian, langsat, mangosteen and breadfruit. Several of these fruits are very spiny and thus require a form of “preparation” beforeDurian fruit in tree eating, which is a procedure that young orangutans must learn from their mothers. In addition, orangutans feed heavily on bark, leaves and other plant parts, as well as termites, caterpillars, ants, crickets and honey. Their dentition differs from other ape species as the back molars contain a thicker layer of enamel. These teeth are capable of cracking even the hardest of nuts. The teeth, strength, and manual dexterity of the orangutan also allow it to feed on some tree barks that are not exploited by other species. These plant parts are high in fiber, which is digested with the aid of fiber-degrading bacteria in the large colon. In turn, fatty acids are secreted that are absorbed and used as a source of energy. A recent nutritional study of captive orangutans has led to the development of a very high fiber dietary gel. It is hoped this will better help meet the high fiber needs of these animals in captivity (St Louis Zoo ZUDUS March/April 2002).

Behavior

Orangutans have complex social relationships and are not as solitary as once believed. While not as social as their African counterparts, they are capable of forming strong social attachments. Their size and arboreal lifestyle make the formation of large groups impractical, since the fruit-bearing trees they inhabit would be able to neither physically support large groups, nor provide enough fruit to sustain a large group. The bond between mother and offspring is strong and the infant stays with its mother for up to ten years. This is the longest childhood of any ape species. Adult females with young often form short-term groups and sub-adult males sometimes associate with adult females. Adolescent females also sometimes travel together when the age difference is minimal. Mature males are generally intolerant of each other. Approximately 60% of the daylight hours are spent in search of, and consuming, food. Each night a new nest is built approximately 40 or 50 feet up in a tree. Although orangutans are almost exclusively arboreal, males will come to the ground to move between stands of trees. Because of their larger bulk, the males tend to stay lower in the canopy than the females, which reduces competition for food when their ranges overlap. Tool use in both wild and captive orangutans has been well documented. This includes making items to scratch with, probe for food with, making umbrellas, and even using sticks to create ladders and bridges. Imitating human behaviors with tools is also documented in captivity and at rehabilitation camps.

Conservation Status

Both species of orangutan are considered endangered, with the Sumatran listed as critically endangered by the IUCN Red List. Both have been covered under Appendix I of the Convention on International Trade in Endangered Species (CITES) since July 1975. Rampant exploitation and conversion of the tropical rainforest for a variety of human interests (primarily for use in the commercial palm oil industry, and logging for industrialized countries), coupled with a booming human population in the area have contributed significantly to the alarming decline. Fires, both unintentional and intentional, have claimed the habitat and lives of many, or have flushed out individuals who are then slaughtered for food. One fire alone, which raged through Borneo in 1997/1998, was thought to have claimed one third of the existing population. In addition, the practice of killing mothers and selling their infants as pets still continues and has led to a staggering number of orphans in captivity. Current estimates put the wild Bornean population at approximately 45,000-50,000 and the Sumatran population at approximately 7,000.

Reproduction

Females reach sexual maturity between the ages of eight and twelve, although in the wild they don't usually give birth until a few years later. The estrus cycle is generally 28 to 32 days. Gestation is 233 to 265 days. The single young is born weighing approximately 1.5 kg (3½ lbs.). Because of the solitary nature of the orangutan, the bond that forms between mother and offspring is very strong. Females do not give birth again for five years, and sometimes it can take as long as eight years. This makes their reproduction rate the slowest of any of the great ape species. Males reach puberty at approximately age seven or nine, but the cheek pads, which are considered secondary sexual traits, may not be fully developed until age 14 or even later. Researchers have reported for some time that females are not receptive to males until the males reach full maturity, with developed cheek pads and a well-developed throat sac capable of emitting loud cries known as long calls. They were also aware, however, that sub-adult males often forcibly copulate with females. Some believed that these males were incapable of impregnating the females but research now disputes this. Researchers have also found that males can stay in a state of arrested development for much longer than was once believed. These findings, regarding the arrested sexual development in male orangutans, have offered a new interesting theory regarding evolutionary strategies for this species. It is now believed that the presence of dominant males in the vicinity causes the arrested development of adolescent males. Since these males are capable of impregnating females it is believed the strategy is one of avoiding conflicts with adult males, while also needing less food to survive. Orangutans in AZA zoos were instrumental in discovering these findings as studies were conducted which tested hormone levels in juveniles, arrested adolescents, developing adolescents, and adult males. The discovery that males in a captive group of orangutans could stay in an arrested state as long as an adult male is still in the group, might have implications for how captive orangutans are managed in the future. (See Scientific American, June 2002).

Lifespan

In captivity orangutans can live upwards of 50 years. Lifespan for wild individuals is probably closer to 40 years.

Sources

 

Orangutan Conservation Issues

Deforestation

As human populations grow larger in Indonesia and Malaysia, the two countries that govern the remaining areas of orangutan habitat, they have begun to place larger demands on their natural resources. For the last few decades, this has resulted in the growth of an ever-increasing timber industry. From the 1960’s onward, the forests were harvested for tropical hardwoods. These particular types of trees grow very slowly so both the trees themselves as well as the ecosystems they support have great difficulty in recovering. As these trees are very large, when they are felled they take out a huge tract of forest around them. During the latter half of the twentieth century, approximately fifty percent of Borneo’s native forest was leveled, primarily for timber production.

More recently, the forests of Borneo have been cut to make way for palm oil plantations. This industry has grown by large leaps over the last few decades. Malaysia is the world’s largest producer of palm oil, having more then 38,000 square km of palm oil plantation. The Island of Borneo alone has 27,000 square km of palm plantation. The slash and burn method often employed in these areas leaves the soil very poor which means its productivity is very short-lived. Once the land becomes infertile, the plantation needs to move on to a new area, and cut down more forest.

As a result of the pressure created by increasing numbers of humans, the timber industry, and the palm oil industry, current estimates put the remaining orangutan habitat at just twenty percent of what it was during the early 20th century. Based on these numbers and the increasing demand for palm oil, some theorize that the entire orangutan habitat on Borneo and Sumatra could be wiped out within the next ten years.

Pet Trade

Although orangutans have been used in the entertainment industry in the past, this practice has slowed considerably. One of the last Hollywood orangutan trainers recently gave up their remaining apes to the Great Ape Trust in Des Moines, Iowa, where they will be permanently retired from their previous “working” life.

A much greater threat to wild orangutans is the pet trade. As babies, they are small, cute, and sociable. This makes them very attractive as pets. What people don’t realize is that they will grow quite large and become potentially dangerous when they reach maturity. This trade is most prolific in Asia. Due to the influence of a popular Taiwanese television show, which featured an orangutan as part of the regular cast, the numbers of pet orangutans went up dramatically in the 1990s. During the height of this fad, the WWF reported that there were more orangutans per square mile in the capital city of Taiwan than in the forests of Borneo and Sumatra.

Though many Asian countries have begun to pass laws about keeping wild orangutans as pets, the trade still occurs. As recently as 2004, a shipment of 100 Bornean orangutans was confiscated in Thailand. It’s estimated that for each orangutan successfully introduced into the pet trade, 4 or 5 others were killed in the process (mothers being killed to simplify the capture and/or babies who simply do not survive the capture and transport process). This one confiscation alone could represent the loss of 1% of the world’s entire population of Bornean orangutans. Stronger laws, harsher penalties, and better enforcement of these laws will be needed to curb this impact to the ape’s dwindling wild population.

Disease

While the threat of disease has not yet accounted for a significant portion of the species’ decline, it has the potential to be devastating. The eco-tourism industry in Borneo and Sumatra is growing. A significant draw for this industry is the opportunity to see orangutans up close. By utilizing the numerous rehabilitation centers (where the apes are habituated to humans), the tourists can be assured of getting a personal encounter. Since orangutans are very closely related to humans, they can typically contract many of the same illnesses that we can. As most of these facilities understand this, the tourists are typically not allowed physical contact with the apes. However, some places choose to ignore that rule with the promise of large tips from wealthy travelers. Even if they adhere to the policies, the close contact can still result in the transmission of airborne pathogens. Since the orangutan population has become so small and so fragmented, any pathogen carried back out into the wild population has the potential to wipe out a significant portion of the world’s remaining orangutans.

Online Resources

AZA Orangutan SSP Status

The Orangutan Species Survival Plan (SSP) guides the management of orangutans living in North American zoos. The SSP plans the strategic captive breeding for both Sumatran and Bornean species of orangutans and oversees many health, behavioral and in-situ studies. Involvement in these studies helps the SSP and zoos understand the needs of orangutans in captivity and wild populations. The SSP also supports the Orangutan Conservancy’s conservation efforts and works to build interest in orangutans by providing zoos with curriculum and materials for school programs.

As of June 2002, there are 73 Bornean orangutans, and 99 Sumatran orangutans held in 54 AZA institutions. (There are also 46 sub specific hybrids in 23 institutions.) The Orangutan SSP not only develops a strategic captive breeding plan for the two species, but also coordinates and oversees many health and behavioral studies. These help us to better understand the needs of this taxon in captivity, as well as to find out how this information might apply to the conservation of wild populations. The Orangutan SSP Field Advisor also keeps the SSP informed regarding the status of projects taking place in-situ. Participating zoos are encouraged to financially or materially support these approved projects. Through specific educational programming, the SSP hopes to coordinate and facilitate education and direct conservation action on an even broader scale in the near future.
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