REPORT

ETHOLOGY – SOCIAL LIFESTYLE OF THE SILVER LEAF (Trachypithecus cristatus)

Introduction :

Silver leaf monkeys also known as Trachypithecus cristatus located at the Bukit Malawati Hill in

Kuala Selangor. The body mass of a male silvered leaf-monkey averages 6.6 kilograms and adult

female averages 5.7 kilograms. Sub-adult males have almost the same size with adult females but

smaller than fully grown adult males. The pelage colour of silver leaf monkey is dark gray with

the tips of the hairs being paler in color giving it a silvered effect. The face is black in coloration

and the hair on the head is pointed. Adult females have irregular patches of white on the inner

portion of the upper thighs. The newborn silver leaf monkey has pelage colour in gold, with the

face, hands, and feet being white. Infants will darken and the darkening process takes 3-5 months

to change to the adult pelage coloration. First, the head starts to fade into yellow orange, then the

head, face, hands, feet, and ears turn dark gray and then black. This species has a sacculated

stomach to assist in the breakdown of cellulose. The silvered leaf-monkey has enlarged salivary

glands to assist it in breaking down food.

Objectives :

1. To investigate the social lifestyle of the troop of animal that had inhabited that area.

2. To understand the social domination in a population of animal.

Materials :

Binocular, timer, pen and paper.

Methods :

1. Work in 7 persons in a group.

2. Any actions done by targeted species is observed and list down for 30 minutes.

3. At the same times, the size of the population of the troop and the individual that lead the troop

is determined.

4. The characteristics that are able to observe from the leader of the troop is determined.

5. Each groups need to prepare a score sheet for all the actions done by members of the troop

after 30 minutes.

6. The frequency of every action done by the troops for 1 minute in the interval of 5 minutes jot

down.

7. One hour is observed.

8. Which of the action is observed is mostly done by the members of the troop? Why?

Figure 1: The map of Bukit Malawati, Kuala Selangor.

Result :

Activity Time Duration (every 5 minutes)

1 2 3 4 5 6

Fighting/Wrestling √ √ √ √

Fight for food √ √ √

Seating around √ √

Swing on tree √ √ √

Take care of their baby √ √ √ √

Jumping √ √ √ √

Looking for lice √

Harrow their body √ √

Give sound ‘kie’ √

Give sound ‘ah-ah’ √ √

Discussion :

Last Saturday, we were observed the activities of Silver Leaf Monkeys at the Bukit

Malawati Hill in Kuala Selangor. In this observation, we only spent time for 30 minutes with

interval of five minutes because of the time limitation. Mostly, local residents call them as

monkeys or ‘lutong’. They are generally harmless towards humans and are sometimes afraid of

us. But, due to the environment in Bukit Malawati, which are flooded with tourists, these silver

leaf monkey adapt to the environment so they can get food given by tourists also. Our sample –

troop of silver leaf monkey with size range 18 individuals.

At the first five minutes, these monkeys are busy hunting for food. Some of them even

fight each other to get the food. They are very obsess with the actions of human such as unzip the

bag and holding something in our pocket, because they think that we are giving food for them.

They can differentiate which food can be eaten. For example, I was giving them a green colour

pen that looked like the green bean. But, they know that it was not the green bean that can be

eaten. When the male silver leaf monkey gets the food, they share their food with their baby.

They bring along their baby wherever they go.

During the second 5 minutes, the troop is sitting around on the ground and some were

swinging on a tree. Some sub-adults were playing wrestling which is common type of social

play. Wrestling is the most common form of play with locomotor play also found. Locomotor

play includes repeated circuits along a pathway where individuals will swing from branches or

drop to the ground from branches. Two in the troop were horrow for other body.

During the third 5 minutes, the troop is sitting around the same place which near tree.

Like before, they doing the same social behaviors like in second 5 minutes. But in this time, we

managed to observe that female adult silver leaf monkey was searching for lice for her baby.

Besides, the infants also emitted sound like “ki” that gave signal to their mother when they felt

unsafe.

During the forth 5 minutes, they were more in a resting state. Some sitting on the tree and

sitting some on the ground. But, the leaders (male) of the troop will make sure his troop not far

away from the troop. The leader will also keep other group males out of the range of the group.

During the fifth 5 minutes, adult male will move rapidly amongst the group and emitted

loud vocalizations when two neighboring groups come together. The adult male was emitted

sound like “ah-ah” in order to control group travel movement. This call was emitted at repeated

intervals. They will lead in the front, when he moved, the other would follow. But, when he

stopped, the other would stop moving too.

During the sixth 6 minutes, the group just finished their meal. The adult male leaded the

troop to another resting place. Here, the juveniles’ males engage in the most vigorous forms of

lay fighting, and they will sometimes play fight with sub-adult males. Some of them searching

lice for other. When resting, juveniles and infants stayed close to adult females.

During the entire observation, we found that most action done by the troop was eating,

follow the instructions by adult male. While the juveniles most of time playing around. Besides,

these silver leaf monkeys also love to hang out of the road barricade by sitting there with only

one thing on their minds - food. 

Conclusion :

In conclusion, every 5 minutes, we could observe different social lifestyle of the troop of animal

that had inhabited that area. But, our result may be affected due to tourists. The tourists gave

them the foods, make all the animals came to them, and affect them the normal daily social

behavior.

References :

Silvered Leaf-monkey (Trachypithecus cristatus). 2007. Retrieved on 28 April 2012 from http://www.theprimata.com/trachypithecus_cristatus.html

David JR. Silver Leaf Monkey at Bukit Malawati Hill. 2009. Retrived on 28 April 2012 from http://blog.malaysia-asia.my/2009/08/silver-leaf-monkeys-at-bukit-malawati.html

Appendix :

Adult female and male with infant

Adult female with her infant

Some of the silver leaf monkey resting on the tree, the infant never far away from adult female, mother.

Our sample - A troop of silver leaf monkey hanging on the tree for resting.