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Tim Sanderson Anth 111 In Orangutans Orangutans Tim Sanderson Anth 111 In Malay orang means person and utan is defined as forest. Thus Orangutan literally means Person of the Forest. Orangutans are found in the tropical forests of Sumatra and Borneo. They are the most arboreal of the great apes and move amongst the safety of the trees from one feeding site to the next. They are so well adapted to arboreal life that they cannot place their feet on the ground, instead they walk on the outside of their curved foot. There is a scattered population of orangutan in Indonesian Borneo, Malaysia Borneo and northern Sumatra.
The different habitats have isolated the orangutan reproductively and geographically from one another creating a degree of difference or two subspecies. There are several different characteristics between the two subspecies of orangutans and it has recently been suggested that they may be a separate species. The Borneo male has relatively large cheek pads, a tremendous laryngeal sac and a square shaped face. The Sumatran male has small pads and laryngeal sac, a ginger coloured moustache, a pronounced beard, and a diamond shaped face. Individuals can also be distinguished chromosomal ly, biochemically, and by their cranial characteristics.
There is a great deal of individual variety in the orangutan. Each orang-utan had a distinct personality and in dealing with such highly intelligent animals in captivity, the keepers knowledge of the individual was probably more important than the knowledge of the overall behaviour patterns (Markham, 1980). Orangutan males, however, appear to be totally intolerant of one another, especially the Borneo males who are even aggressive towards females and infants. Male orangutans participation in social groups is limited to sexual consort ship with females.
However, the Sumatran males tend to stay with females for a longer period of time usually until the birth of the infant. They may stay longer with their partner because of the presence of large predators absent in the Borneo habitat. The orangutan has a menstrual cycle of 29 - 30 days, menstruation lasting 3 - 4 days. The Gestation period lasts slightly less than nine months. Offspring pass through three stages, infancy (0 - 4), juvenile (4 - 7), and adolescents (7 - 10). Mother young relationship lasts for a long time, the young usually stay with their mother until they are mature.
Female Orangutans are not sexually mature or fully grown until the age of twelve and will not have their first offspring until they are at least fourteen. Males become sexually mature and fully grown at the age of fifteen. The cheek flanges of the male easily recognize the differences between adults and semi-adults. The flanges in the Boreal male curve out ward from the face and develop around the age of eight and are not completely grown until the age of fifteen. Sumatra flange development begins at the age of ten and is not complete until the early twenties. The flange in the Sumatra orangutan lie flat against the face and give a wide facial appearance especially in the mid facial region.
The life expectancy of orangutans in the wild is not known, but captive orangutans have been known to live up to fifty years. Orangutans are sexually dimorphic. Males are approximately twice the size of females and weigh about 220 lbs. and reach a height of five feet. It is believed that the males larger size may be an adaptation for mating because there is strong competition among males for females.
The pendulous laryngeal sac, when inflated, increases the tone of the animals voice, producing long calls. In both subspecies (Borneo and Sumatran) calling acts as a spacing mechanism between the males and also advertise the location of the highest ranking male to the mature females. (Rijksen, 1978). The long call of the Borneo male is long and drawn out where as the Sumatran is much shorter and has a faster tempo. The difference may be attributed to the larger throat pouch the Borneo has. The reason for the different calls is unclear. They may be related to the terrain each subspecies inhabits.
The faster call of the Sumatran may be more effective in the rugged, mountainous terrain. The longer call of the Borneo may be due to the wide distribution of this race. A large portion of an orangutans day is spent looking for and consuming food. Their diet primarily consists of fruit but they also eat leaves, bark, flowers, insects, and birds eggs. One of their preferred foods is the fruit off of the durian tree, it is supposed to taste like sweet garlic. After they have finished eating and bedtime comes around the orangutans build themselves a new nest forty to fifty feet up in a tree made of boughs.
Like the other great apes (chimpanzees and gorillas), orangutans are highly intelligent. Tests have indicated that their intelligence is relatively similar. Wild orangutans use their intelligence to solve problems usually related to arboreal living and food gathering. In captivity, however, they have been trained to perform tricks and to use sign language. They have also made tools to throw at humans, get food, and gain leverage. Today, the total number of orangutans ranges between 20 - 27, 000.
They are now endangered primarily because their habitat continues to be destroyed and the practice of killing the mother in order to capture a baby for animal trade. Even though they are protected by international laws, it is difficult to enforce them. Orangutans are inhabit the forests on the islands Sumatra and Borneo. Through evolution and reproductive and geological isolation two sub species have emerged (Borneo and Sumatra). They generally live alone with the exception of the long term relationship between a female and her young. When orangutans do meet one another they are very tolerant and aggression is rare, unless two mature males meet each other.
Males maintain their distance from on another with long calls, these also advertise their location to adult females. Orangutans are generally fruit eaters, because fruit is abundant in the forests they inhabit. They lead a very solitary life. The population continues to decline because of habitat loss, and fewer than 30, 000 orangutans are thought to remain in the wild.
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