Primates of the Gunung Leuser Ecosystem

Twice this past year 1996-1997 the grade 6, 7, 8 class of ISOL took trips to the Gunung Leuser Ecosystem. Both trips we took were to the Sekunder area near Besitang on the East side of the ecosystem. The observation site that we worked at is on the border of the forest and the 12,000 hectares (30,000 acres) that was slashed and burnt three years ago. The scientists in the area are trying to compare the life in the somber wasteland to the small amount of lush, succulent forest left. The Sekunder area is lowland - that is why scientists are actively studying that area. Because the Sekunder area is lowland, it is home to some of the last wild Sumatran Elephants, Sumatran Tigers and Sumatran Rhinos.

The two trips that we made were to explore and examine the forest with the scientists. Our first trip from November 4th to 6th was to choose a topic to study. The second trip from April 14th to 16th was to study the topic of our choice.

On the first trip I saw many animals and plants in the extraordinary jungle. Most interesting to me were the primates. The primates of the area are the orangutan, the white-handed gibbon, the siamang, the long-tailed and pig-tailed macaques, Tomas-leaf monkeys and the silver-leaf monkeys. There is also another very small primate the slow lorry, which scientists are not sure exists in this area. When we were there we also conducted a survey of the small mammals, in the area. We set up small traps in many different places - in low brush, in moist areas and in dry areas. The traps had trap doors that snap down when the animal pulls on the baited hook. For bait we used bananas and peanut butter. We caught many different species of field rats. The most common was the Malaysian Field Rat.

Primates are mammals that consist of many different classes and species. There are 2 kinds of primates: Anthropoids and Prosimians. Anthropoids are humans, apes, and monkeys. Prosimians are aye-ayes, galagos, lemurs, lories, pottos, and tarsiers. The primates in the Leuser Ecosystem are all anthropoids. Anthropoids are the largest of the primates. They have highly developed brain and are very intelligent animals. Old World monkeys live in Asia and have many human features. Their hands are like ours with four fingers and a thumb. Their hands also have fingernails. They use their hands and feet to grab objects as we do. For orangutans and gibbons, the most important sense is vision. Orangutan's and gibbon's eyes can judge depth. Their vision is vital; if they had no stereoscopic vision they could not find food or climb, swing and jump from trees. For monkeys, the tail is a very important body part. It is used to hang from branches so that it frees the hands to grab hold of fruit or other branches. Gibbons and orangutan have no tails because they are apes.

Macaques

Over a period of time I observed the macaques that live in Bukit Indah. One weekend we specifically observed Hairy, a male long-tailed macaque. At 1:30 Sunday, February 1, 1997 he had a large piece of fruit in his hands. Another monkey came along and tried to take a piece. Hairy ran up the tree. Hairy is not a shy monkey. The closest that I got to him was about two meters. After a few minutes Hairy made his way to the ground five meters away where we got a better look at him. Hairy has round, yellow-green eyes and two pointy black ears. His hair is brownish grey, his stomach is white, and on top of his head he has a small puff of hair that is sandy red. His face is narrow and pinkish with a black stripe on his cheek. He uses his mouth to open seeds on the tree. He has four long, sharp canine teeth - two on the top and two on the bottom - and all of his teeth are very white. His hand is like ours except that his thumb is short and not very useful. We observed him for just over 30 minutes. After that he went to where we could not see him. This was the first time I got a real good look at these monkeys.

Many days I have tried to see the macaques at different times during the day I also look at 6:00 a.m., 2:00 p.m. and 7:00 p.m. The only time I saw them was at 1:30 p.m. on a cloudy afternoon. I think they move from tree to tree around the compound to find food.

Orangutan

The orangutan is the most intelligent primate in Asia. They are also the largest. A male orangutan, when standing, can reach 1.4 meters in height. The adult male can have up to a 2.4 meter arm span. The male weighs up to 70 kilograms. Orangutans spend a lot of time in the trees as well as on the ground. They remain in the trees mainly to sleep and to eat. Orangutans sleep in nests built of twigs, branches and leaves.

Each night an orangutan will build a nest in a tree on a branch to sleep in. An orangutan will never sleep in the same nest twice. The orangutan nest looks like a large bird's nest. When I was in the Gunung Leusur Ecosystem I saw an orangutan nest. It was midway up a tree. The nest is built for only one orangutan because the orangutan is not very social. Orangutans live alone and avoid other orangutans except in mating season. Two will live together only if a mother is caring for her young. When babies are born they weigh 1.7 kilograms, and they travel on their mother's back. By the time an orangutan is three years old it will start to wander off by itself.

Zoo orangutans put on a lot of fat like humans, especially if they sit around all day. Captive orangutans tend to have a longer life. A male Orangutan that is too heavy for a tree will live on the ground and eat ground plants. In the past, tigers would feed on the orangutan. But there are less and less tigers every day. Wild Orangutans live a more exciting life in the trees living for as long as 20 years, while captive orangutans may live up to 30 years. Sumatra's and Borneo's Orangutans are quite different in physical appearance. Orangutans of Sumatra have lighter hair and a thinner face. They are very intelligent and have short fingers. The Orangutans of Borneo have darker hair and skin and their fingers are longer. The Orangutans from Borneo appeared before the Sumatran orangutan.

When I was in a local zoo I encountered a large male orangutan. BoBo is about 26 years old and weighs about 300 pounds. He was over 4 feet tall when he was sitting. His hands could have easily been 1 foot long. Male Orangutans get large check pouches as they get older; as they get older they also develop massive throat pouches. These facial features make the male's face look very different from the females. Chris, a Canadian that works at the zoo, said that BoBo is about as strong as a dozen men. The zoo in which he lives is not a very nice zoo; the cages are not nice. People often steal and kill the zoo animals! BoBo is detrimentally affected by his visitors. People think that it is funny to see an orangutan smoking. As a result of this BoBo has been smoking for about 20 years, and he has smoker's cough. If he were in the wild he would probably not be alive. BoBo is so unhealthy Chris said they are just waiting for him to die.

There are about 5 orangutans in the zoo and they are too intelligent to be there. Although they are in a cage that has nothing but a rice sack, that is not going to keep them from having fun. One female has been in the same small cage for six years. She is very interesting to watch. She ties the rice sack to the top of the cage and winds it up and spins around in circles. Chris said that once she put her finger in a can and cut it. She did not want to have medicine put on it. Chris pretended to clean a cut on his own hand, then gave her the cotton and the bottle and she did it herself. She is also a great pick pocket. When people come by her cage she will take wallets, bags and sun-glasses.

Another female puts her arms and head in a rice sack and tries to walk around but ends up falling down. This same female will give herself a bath if she is given soap and water and will clean herself and the sack that she sleeps in. Orangutans are very playful. They like to grab T-shirts and people's arms. Orangutans are very ticklish and if they are tickled they show a very human-like response. They will make laughing sounds and sounds with their lips.

Orangutans have had a long history with man. Early man hunted and ate the orangutan. There are bone fossils that are 35,000 years old found in caves in Indonesia and China. Nowadays people don't hunt the orangutan for food, but many are captured as pets. Most Orangutans die because of logging and habitat loss. Most people are trying to save Orangutans by building rehabilitation centers. The main rehabilitation centers are Bukit Lawang on Sumatra and Sepilok Rehabilitation Center in Borneo.

Gibbons

Each morning the rain forests fill with the exquisite singing of the gibbon. In the Gunung Leuser Ecosystem there are two kinds of gibbons: the white-handed gibbons and the siamang. Siamang and white-handed gibbons are lesser apes. Like the orangutan they have no tails, but have sitting pads on their butts. These sitting pads guarantee a comfortable night in the tree tops. Unlike the heavyweight great apes the gibbon only weighs 10 to 20 pounds, and siamang weighs 20 to 30 pounds. The dense fur of the gibbon and Siamang makes it look much larger. They live 100 to 150 feet high in the canopy. In the canopy there are more fruits and birds eggs for them to eat. They swing from tree to tree using their long arms to find food. Gibbons live in family groups often consisting of one adult male, a few females and their young. Gibbons are found in the lush, tropical rain forests of Southeast Asia.

White-handed gibbons and Siamang live and travel in groups. They move around in the trees looking for food. They do not wander randomly and nomadically through their home range. Each four or five days the Gibbons and Siamang swing through the trees singing a "duet," sung by the adult male and female. They may be joined by a few older, mature individuals. The singing of a group of white-handed gibbons or Siamang can last up to 30 minutes. There is a very distinctive difference in the two calls. The Gibbons "owa owa" song consists of whooping sounds.

The Siamang "imbu" are yelp-like barks that are an octave lower than the gibbons' call. These loud songs can be heard up to 2 kilometers away, and are made by the gular sac under the chin. Sometimes two groups of gibbons will interact with each other. For example, adult males sitting in trees in their respective territories may shout loud, elaborate solo songs at each other. They may also perform brief spurts of extremely vigorous sounds. They will also send branches crashing to the ground. This is essentially harmless. It can escalate into a fight that can result in the death of one of the males. Sometimes the females will move into the action if she needs to aid a mate that is being chased.

Gibbons and Siamang have long strong arms that are great for swinging around in the trees. There is no branch that these apes cannot make their way to. Vines connect the trees forming numerous horizontal strata. Gibbons have the ability to swing and leap distances up to 30 feet between the branches. In the local zoo there is a gibbon that was trapped by its wrist and it is all cut up. This animal can never be rehabilitated because of the damage to its arm. In the towering trees, these lesser apes will find an abundant supply of figs, mangos and other fruits. They also eat leaves, insects, flowers and some rare items such as honeycomb and fungi. Fruit is the single largest component of their diet. They spend most of their feeding time eating fruits.

Langurs

Langurs are spectacular and beautiful animals. Langurs are monkeys that have a small head, medium-size body, and long tail. Langurs make magnificent jumps and occasionally swing by their arms. In the Leuser Ecosystem there are two kinds of Langurs, often called "leaf monkeys". There is the silver-leaf monkey and the Tomas-leaf monkey. Silver-leaf monkeys have a dark silvery-black fur. The Tomas-leaf monkey has more grey and white fur. Both species have a broom of hair on the top of their heads.

Leaf Monkeys get their name because of the great amount of leaves they eat in their diet. They also eat flowers, seeds and unripe fruit. The monkeys possess a sacculated stomach which is less acidic than in other primates guts. This digestive system allows them to digest leaves and unripe fruit. Langurs being eaten by predators is rarely observed. Once a raptor was seen trying to catch a baby, and a python was found that had swallowed a langur.

The langurs don't do as much calling as the gibbon, but they do call. The males' call sounds like coughs and the females' sounds like a hiccup. When langurs are on the ground, which they rarely are, one loud cough can send them all rushing in to the trees. The langurs live in groups that consist of one adult male, several adult females, and their young. The group will share food, but the male is dominant over the females so he occasionally will use his position to obtain the more flavourable fruits. Friendly behavior is also observed such as grooming and playing.

Finding all these primates in the jungle is difficult. To do so, find a place in a forested area and sit and wait. You need to be patient and have a sharp eye. You need to be able to turn and look in any direction when you hear calling or crashing in the trees. And most of all you need to be quiet!

I think that the only way these animals have a chance is if we teach the local people about the rain forest and its importance. By educating local people we can stop poaching and encourage tourism in the forest.

bxjacoby@jak.mobil.com