INTERACTION BETWEEN ADOLESCENT AND JUVENILE ORANG UTAN UNDERGOING REHABILITATION AT MATANG WILDLIFE CENTRE, MALAYSIA

BOLHASSAN BIN HJ GULONG

This study examined interactions between individual orang utan (Pongo pygmaeus) which are undergoing a rehabilitation programme at Matang Wildlife Centre. The programme was started in1997 and outdoor jungle training began in July 1999. The subjects were five juvenile and adolescent orang utan aged between five and eight years old, two males and three females. Observations were made on five days in June 2001, each orang utan being observed for one day. These observations showed that most of the subjects still tend to stay in groups, except the biggest male and the oldest female, which have started to adopt the orang utan’s usual solitary lifestyle.

Orang utan normally live solitary lives (unlike all other apes), and the only social contact apart from mating is between juveniles and their mothers (Bennett 1998). These rehabilitants seem to form social groups and the study was intended to document this.

The orang utan studied were three adolescents and two juveniles. These animals had been surrendered by their owners to the Forestry Department and prior to their acquisition had spent most of their early life in cages as pets. Upon their arrival at the wildlife centres (Semenggoh or Matang), each had been given a house name to identify them and call them at feeding time. Details of the orang utan are given in table 1. All the subjects have shown improvement in almost every activity such as foraging, nest building and awareness of hazards since the jungle training began in 1999.

Table 1: Details of orang utan

The objectives of this study were: -

• to monitor and collect data on the distance between the subjects when they were free in the forest,
• to observe their behaviour and interaction between each other, and
• to understand their social behaviour.

The study was carried out on five non-consecutive days in June 2001. One individual orang utan was followed each day, from 0630 until 1930 hrs or until all movement and activities had stopped. The animal’s activity and the distance between the subject and the other orang utan were recorded every 30 minutes.

Study Area
The study was conducted at Matang Wildlife Centre, Sarawak. The Centre covers 179 hectares of mixed dipterocarp forest and karangas forest. The rehabilitation programme is based on the "feeding platform system" (Abdul Kadir and Abu Bakar, 1999) and had reached the third platform, sited approximately 1.5 km south-west of the Centre. The five animals’ movements centred on this platform. There were no other orang utan in the area.

Distance from nearest other orang utan
Overall, the subjects tended to stay within 20m of another orang utan. The percentage of observations below 20 was 73%, with only 17% above 50 meters. There were differences between subjects, as shown in Table 2, and Dominic spent most of his time more than 50m from the others.

Table 2: Distance between the subject and the nearest other orang utan.

Distance between pairs of subjects
The most ‘intimate’ pair was Chocolate and Sing Sing, which were less than 10m apart on 94% of observations. The most ‘distant’ pair were Dominic and Ganti, who were more than 50m apart on 56% of occasions. See table 3 for further details.

Table 3: Distance between pairs of subjects less than 10 metres.

Interactions (social behaviour and vocalisation)
A squeaking sound is the most common vocalisation produced by orang utan. Squeak vocalisation is seldom heard from younger orang utan. The sound may be an invitation to travel together or just to inform the others when they want to move. However, sometimes when the other subjects paid no attention, a "spluttering sound" was produced. This sound is produced by expulsion of air through compressed or closed and slightly pouted lips (Rijksen, 1978). The spluttering sound is often heard from the orang utan when we tried to chase them away. It seemed that this sound expresses either anger or disappointment. We also recorded some other vocalisations such as "chomping" and "kissing". The chomping sound is produced with the tongue in the partly closed mouth while the animal makes chewing movements with its jaws (Rijksen, 1978). In one occasion, we observed Chiam producing this kind of vocalisation and acting obviously aggressively, as if about to attack. I believe that this sound is produced when the orang utan feels threatened. The kissing sound consists of sucking in air through pouted lips and it is like a loud sucking kiss. It was usually heard from Ganti when she was left alone or when she intended to approach the others. A screaming sound was also heard when the smaller orang utan were being bullied by the larger ones. The screaming sound seems like to express fear or distress (Rijksen, 1978).

Playing behaviour
Playing usually occurred during and after feeding time for orang utan because it is the time for the group to get together. Activities observed during playing were wrestling, chasing each other, rolling, swinging or dangling from branches. All of them were involved in these activities and the male orang utan usually spent a longer time in play. The most common playing behaviour observed was wrestling: it usually done by the male orang utan and most of the time they wrestle on the ground. Chasing involves both sexes, with female always being the one chased. Sometimes subjects played with objects or tools, such as sticks or small tree branches, using the object to dig the soil as if searching for food.

Other behaviour
One of the behaviours observed was grooming, which was usually done by female subjects. During grooming the orang utan sometimes scratch their neck, back and sometimes pick something between their teeth or pick their nose. These animals also like to imitate human behaviour, such as bathing and washing at the nearby stream.

Another behaviour observed from the subjects was self-stimulation. The subjects were spotted stimulating themselves either by rubbing their hand or foot on their penis.

Adult orang utan are the least sociable primate in the wild and they always like to travel alone, except the females, which like to stay together with their offspring. Young orang utan depend on their mother for at least 5 years (Bennett, 1998). In the rehabilitation programme, most of the subjects were still very young, and at this stage they would normally still depend on their mother.

Dominic and Chiam are the biggest and oldest subjects. They like to travel alone and distance themselves from the others. There has been an improvement in their survival skills and they are beginning to adopt the orang utan’s solitary life style. Dominic in particular has matured in his activities and is the most dominant among the rehabilitants.

The close interaction between the orang utan in this study may be due to –

• the absence of maternal care;
• the need to have close companions;
• interdependence between individuals.

Two of the five rehabilitants, Dominic and Chiam, seem to have become reasonably independent, more so than they were before the jungle training began. The study should be repeated in a year’s time to see if the subjects are becoming more independent and solitary in their behaviour and to assess the success of the current rehabilitation methods.

Bennett, E. L. (1998). Natural History of Orang-Utan. Natural History Publications, Kota Kinabalu.

Abdul Kadir Mohd. Hussain and Abu Bakar Azman (1999). Preliminary report on the orang utan (Pongo pygmaeus) rehabilitation programme at Matang Wildlife Centre. Hornbill, 3.

Rijksen, H. D. (1978). A Field Study on Sumatran Orang utans (Pongo pygmaeus abelli, Lesson 1827). Ecology, Behavior and Conservation. Veenaman and Zonen, Wageningen.