Orangutans Essay, Research Paper

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

chromosomally, 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 keeper’s 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 “consortship” 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.