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Magill's Encyclopedia of Science: Animal Life Orangutans Type of Animal Science: Classification Fields of Study: Anatomy, conservation biology, wildlife ecology, zoology Orangutans are large apes with orange to reddish-brown shaggy hair. They have very long arms and no tail. They survive solely in the jungles of Borneo and Sumatra, where their habitat has been destroyed to the point that they are listed as a threatened species. Principal Terms arboreal: living completely or primarily in the trees bipedal: walking on only two feet, as humans do quadrupedal: walking on all four feet sexual dimorphism: the occurrence of anatomic and physiologic differences that distinguish males from females of a particular species The name “orang-utan,” commonly written in the hyphenated form, comes from two Malay words: orang meaning “person,” and hutan meaning “forest or jungle.” Thus, Malaysian orang-utan means “persons of the jungle.” Since these animals are very humanlike and live secretive lives in the dense jungle, the origin of the name makes sense. Orangutans are considered to be a threatened species. Less than twenty thousand are believed left in the wild. Orangutans are the second largest of the apes, and show marked sexual dimorphism. Males may grow to be 220 pounds (100 kilograms) and females about half that. The arms of a full-grown male may reach a span of 7 to 8 feet (2.1 to 2.4 meters), and their hands are longer than any other primate. These arms and hands are ideally adapted for the arboreal life. Comparatively, the legs are short and weak; there is no external tail. While adult males with arms extended (swinging through the jungle) may appear to be enormous, when standing erect on the ground they rarely exceed 4.5 feet (1.3 meters) in height. Females, by contrast, reach only 3.5 feet (1.1 meters). Habitat Two to three million years ago, orangutans lived as far north as China and as far south as Java. As land bridges formed during the Ice Age, orangutans moved south in search of a warmer climate. Today they can only be found on the Indonesian islands of Borneo and Sumatra. Orangutans are the only truly arboreal apes, spending most of their life in forest trees. Their anatomy is well suited for this lifestyle. They walk up trunks using irregularities in the bark to give a grip to fingers and toes, and proceed silently through the middle stories of the forest. These middle stories are especially well suited for horizontal travel, where densely growing trees poke up into the canopy. Often vines are used for quickly moving up and down to get to the next horizontal branches. Orangutans do not jump; they climb and walk the branches on all four legs. They may also sit, recline, or hang in a variety of positions, including suspended from both feet or from one foot and one hand. On the ground, orangutans are normally quadrupedal, although they occasionally walk in the bipedal position. Their weight is borne by clenched fists with the palm touching the ground (unlike gorillas and chimpanzees). Their walk is similar to that of a dog, with diagonally opposed limbs moving forward together. Orangutans live alone, in pairs, or in small family groupings. They build nests in the trees from groups of small branches, bent or broken and laid across one another, then lined with smaller branches that are patted down into a circle of approximately three feet in diameter. Nests are placed ten to one hundred feet above the ground and are difficult to spot. Nests may be built new each night when animals are moving about, but may remain intact for several months after being built. While moving and at rest in trees, the orangutan grasps vegetable and animal matter within its reach, testing each one as food. It prefers a variety of jungle fruits as its principal diet, but also eats or chews an infinite variety of buds and leaves, flowers, bark, epiphytes, canes and roots, honey, and even fungi. It forages and eats at leisure, picking fruits with cupped hands and spitting seeds and shells back out of its mouth. Orangutans satisfy most of their need for water by taking it in with their moist food. When on the ground they drink from a stream or lake by bending over from a standing position. They have also been seen to squat down and use their hands to spoon the water into their mouths. Reproduction and Development Orangutans reach maturity at about ten years of age, and can begin breeding at any time thereafter. Mating begins with a male singing a song, a low hum that increases to a deep roar before decreasing again. Often playful wrestling, touching, and other acts precede mating. Mating occurs in trees, face to face, usually in a hanging position. Mating may occur repeatedly over a period of several weeks. The pair then separates and each goes its own way. Males play no role in parenting. Female orangutans have a menstrual cycle similar to that of a human female. It lasts twenty-nine days, with a slight flow of blood for three to four days. Pregnancy lasts nearly nine months, and newborns generally weigh 2.25 to 3.25 pounds (1.1 to 1.6 kilograms). The infant clings to the mother’s fur and the mother holds the infant with one arm, usually over the hip. This leaves three limbs for traveling and feeding. The youngster nurses for two to three years, with solid food (chewed up fruit) being added periodically. By the end of the first year the youngster begins to explore away from its mother, but remains within eyesight at all times. By age four, a youngster is pretty much on its own, feeding itself and roaming freely. At that point, the mother is able to mate again. Offspring have only about a 50 to 60 percent survival rate in the jungle, with accidents and disease striking many young orangutans. Orangutans are shy animals that have only one natural enemy: humans. Currently, orangutans are protected by law in all of their territory, but poaching and illegal logging continue to threaten the survival of the species. Unless large areas of undisturbed jungle are set aside as sanctuaries, the orangutan may have a hard time surviving in the future.
Kerry L. Cheesman See AlsoApes to hominids; Baboons; Cannibalism; Chimpanzees; Communication; Communities; Evolution: Animal life; Evolution: Historical perspective; Fauna: Africa; Gorillas; Groups; Hominids; Homo sapiens and human diversification; Human evolution analysis; Infanticide; Learning; Lemurs; Mammalian social systems; Monkeys; Primates. Bibliography Galdikas, Biruté. Reflections of Eden: My Years with the Orangutans of Borneo. Boston: Little, Brown, 1995. An enjoyable, easy-to-read biography of the world’s leading orangutan authority. Filled with pictures and stories of individual animals. Galdikas, Biruté, and Nancy Briggs. Orangutan Odyssey. New York: Harry N. Abrams, 1999. Exquisite photographs of the work at Camp Leakey and beyond. Clear, easy-to-read text. Kaplan, Gisela, and Lesley Rogers. The Orangutans: Their Evolution, Behavior, and Future. Cambridge, Mass.: Perseus, 2000. An inclusive, yet readable summary of what we know about the biology, behavior, and intellectual capacity of orangutans. An excellent source of information. Macdonald, David, ed. The Encyclopedia of Mammals. New York: Facts on File, 1984. Good description of orangutans, with comparison to other primates. Russon, Anne. Orangutans: Wizards of the Rain Forest. Willowdale, Ontario: Firefly Books, 2000. A report of the author’s ten years working with orangutans in Borneo. Good history of orangutans; excellent reference list. |
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