Changes in diet, home range and habitat use of a released gibbon in the Khao Phra Theaw Non-hunting Area in Phuket, Thailand

Suwit Punnadee and Guillaume Pages

Abstract

A 5 years old male lar gibbon (Hylobates lar) released on the 30^th of November 2001 was followed in the Khao Phra Thaew Non-hunting Area in Phuket, Thailand, to know how its home range was evolving during the time. Since January 2002, the gibbon has been spending more time closer to a main nature trail (tourist trail). It was so decided to try to push it further in the forest by the feeding basket he has been using since the release. For this purpose the feeding basket was moved deeper into the forest over a period of five weeks during May and June 2002. The amount of food available in the basket was also reduced to induce the gibbon to forage on its own for natural food resources. Food diversity, home range and habitat use were recorded before and after moving the basket. The gibbon ate more green leaves after the feeding system was moved. In both conditions, 30 to 35 per cent of observed feeding was on bamboo shoots, probably due to the nature of the forest and the tendency to stay closer to the ground than wild gibbons. Home range increased from 2.5 to 5 ha. The gibbon also spent less time by the main nature trail after moving the basket (6 %) then before (13 %).

Key words: lar gibbon, home range, food variability

Introduction

Rehabilitation of gibbons (and of animals in general) is a process which consists in releasing captive individuals (from whatever source) in the nature, after behavioural training. The delicate step from the cage to the forest can bring some difficulties. In the present study we faced some of these problems and tried to solve them to insure a successful release. The problems met by a released gibbon and considered important for this study were: the change in diet, which occurs from captive to natural condition; the reduction of food provisioned by humans and the subsequent step for the gibbon to provide food on his own; the reduction of

human contact (especially if a single individual if released); the change in the favorable height from the ground, which has to be increased of at least ten meters to meet the normal average height at which wild gibbons use to stay.

Furthermore the release concerning this study led to another problem due to the fact that no others gibbons were present in the area chosen as release site (Khao Phra Thaew Non-hunting Area, Phuket). This means that no defended territories existed in the site and the released gibbon was not constrained to a defined area but could choose its home range wherever it wanted and change it (no boundaries created by others groups).

The aims of the release followed in this study were: 1) increase of intake of food from the forest and increase of variety in diet and intake of green leaves. 2) decrease of the workload of the staff by reducing and eventually stopping provision of food. 3) increase of the home range used by the gibbon (the use of space matching the distribution of resources that animals use, it was hypothesized that by moving the feeding basket further into the forest would increase the gibbon's home range). 4) increase of the height at which the gibbon used to stay in the forest. 5) decrease of the interactions with visitors by the main nature trail.

We tried to achieve these purposes using the feeding basket which provided food to the gibbon, by moving it in the forest and reducing the amount of food put in it.

Following different studies, the diet of wild lar gibbons consists generally of 60 per cent of fruits, 30 per cent of leaves and 10 per cent of animal matter, mostly insects (Chivers and Raemaekers, 1986; Chivers, 1984). Day-to-day fluctuations in dietary proportions can be marked and proportions of food types vary also between months, because of the seasonality (Chivers and Raemaekers, 1986). H. lar is classed as a frugivore (Ellefson, 1974), fruit-pulp seeker. Fruits are normally eaten for first and last feeds (more strongly at first than last feed), while young leaves are not eaten for these feeds (Raemaekers,1978). There is also no reason to believe that group members differ in their choice of certain food at certain times, as it was tested by Raemaekers (1978).

Wild lar gibbons have a home range from 16 to over 50 ha (Chivers and Raemaekers, 1986; Carpenter, 1940; Ellefson, 1974; Chivers, 1972 from Brockelman, 1975). Following Brockelman (1975), they live in not too dry and open forests; they stay in the middle and upper layers of the forest canopy, rarely coming to the ground (in dry season, for water). The activity budgets can be divided in feed: 3.6 h, travel: 2.8 h and rest:2.2 h.(Raemaekers, 1979)

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Methods

The present study had been carried in the Khao Phra Thaew Non-hunting Area situated on the island of Phuket, Thailand. The site is a mountain range reaching 400 to 450 m above sea level. It is surrounded by village plantations and covered by 22 sq km of original semi-evergreen rainforest and about 2 sq km of secondary forest. The area receives between 2,350 and 2,700 mm of rain annually and has an annual mean of temperature of 28^C.

Figure 1: Mai's activity (1) Eating from the feeding basket at F1. (2) Foraging after rain. (3) Resting.

The subject of the study was an adolescent (5 years old) male white-handed gibbon (Hylobates lar) named Mai (Figure 1). Mai was born in July 1997 at the Gibbon Rehabilitation Project of Phuket, Thailand, and was released in November 2001 in the forest with three other adolescent gibbons. The group split up two weeks after the release and since January 2002 Mai established his home range in an area close to the Gibbon Rehabilitation Project station where captive gibbons are kept during the rehabilitation phase, close to an entry of the park (Figure 2). The gibbon being seen in several occasion close to a main nature trail (tourist trail) and even foraging from a dustbin, a feeding basket was provided every day with fruits and vegetables and moved two times deeper in the forest (from January to May 2002) until reaching the start location used for this study. (Figure 2, 5, 6)

The study was divided in two periods. The first period (baseline) started on the 8^th of May and finished on the 18^th of May 2002, with 8 days of observation and 35 hours of contact. The second period started on the 19^th of May and finished on the 26 of June, with 12 days of contact and 45 hours of data collected. The activity, position and height of the individual were collected every 5 minutes; the kind of food eaten was also recorded.

A network of trails at 50 m intervals covering an area of 7 ha was used to follow the gibbon . During the study period the feeding basket was moved 5 times to 4 different locations (Figure 5, 6)

Results

Food diversity

The differences observed in Mai's diet before and after moving the feeding basket deeper in the forest and reducing provided food are shown in Figure 3.

Mai ate significantly more green leaves (X²=4.52, p<0.05) after the feeding system was moved. The reduction of provided food resulted in less intake of the gibbon from this source (X²=7.62, p<0.05). Mai spent less time feeding on the provisioned food and thus had to increase its intake of leaves and other forest fruit although the latter do not show any significant increase (Figure 3). Some examples of wild food types eaten by Mai are Garcinia sp. (Guttiferae) Sandoricum koetjape (Burm.f) Merr. (Meliaceae) Artocarpus sp. (Moraceae), Gigantochloa sp. (Gramineae) Alstonia sp. (Apocynaceae) Dillenia sp. (Dilleniaceae). (see also Figure 4)

It is interesting to note that in both conditions 30 to 35% of the observed feeding was on

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Figure 3: Differences in diet before and after moving the feeding basket.

Figure 4: The example of wild food that Mai ate. (1) Garcinia sp. (2) Sandoricum koetjape (Burm.f) Merr. (3) Artocarpus sp. (4), (5) Gigantochloa sp. (6) Alstonia sp.

bamboo shoots, which are not generally believed to be part of any gibbon's species diet in such high proportion. This could be due to the presence of secondary type forest in the lowest part of Mai's home range, offering a lot of bamboo and young trees (no more than 3 meters high) as food resources. Furthermore, as a captive born animal, Mai would have a tendency to stay closer to the ground than wild gibbons would, thus adding to the problem of successful releases as the forest offer plenty of resources at a low level where the newly released animal is most comfortable at.

Home range and habitat use

The area size of the forest used by Mai increased from 2.25 hectares in the baseline period to twice the size (5 hectares) during the second period (Figures 5 and 6).

Figure 5: Home range (2.25 ha) used by Mai before the feedding system was moved.

F1 is a location of the feeding system.

Furthermore it was also found that the gibbon spent significantly less time (X²=7.65, p<0.05) by the main nature trail during the second period (6%) than during the first period (13%).

The average height at which the gibbon used to stay in the forest was 7.41 m during the first period and 7.71 meters during the second period. Comparison of the two height showed no significant differences (Figure 7).

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Figure 6: Home range (5 ha) used by Mai when the feeding systems were moved.

F1, F2 , F3, F4 and F5 are the locations of the different systems.

Figure 7: Comparison of height used by Mai before and after the moving of the feeding basket.

But when analysed meter by meter a few significant differences showed up. Mai did

spend more time during the baseline period at 1 m (x²=3.90 p<0.05) and 12 meters (X²=16.17 p<0.05) above ground than during the second period, while it also spent significantly more time at 11 m (X²=6.82), 15 m (X²=4.82), 16 m (X²=8.41) and 20 m (X²=7.43 p<0.05) mark during the second period than during the baseline week. The difference at 12 m could be explained by the fact that the resting tree used during the baseline period was 12 meters high, while the resting trees used during the second period were higher at 15 and 16 meters above ground. The 20 meters mark was reached during the second period and represents a feeding tree that still fruiting at the end of the observation period.

Behaviour budget

It was hypothesized that by moving the feeding system, and forcing Mai to feed and forage by its own on food available from the forest, its behavioural pattern would be different during the second period. It was believed that Mai would have to move and forage significantly more during it. However no significant differences were found (Figure 8).

Figure 8: Comparative behavioural pattern.

Conclusion

In conclusion we can say that the moving of the feeding basket and the reduction of provisioned food achieved the aims of increasing the home range size and the intake of green leaves and decreasing the time spent by Mai near the main nature trail path frequented by visitors or tourists.

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In the expectations not met we can include the increase of time spent feeding and foraging and moving through the area, and the decrease of time spent interacting with visitors (although one should keep in mind that few data were collected for this specific behaviour, and thus significance might not show).

The moving of a feeding basket to force a released gibbon to spend more time in the forest is obviously a practical and efficient technique. Coupled with a slow and steady decrease in the provisioned food, this will force the gibbon to explore further the forest in search of new feeding areas as its feeding basket does not support its food intake for a full day. However the feeding basket should always be filled with favorite foodstuff and food that is not available in the forest naturally (such as mango in our case). This will keep the gibbon interested in the feeding basket and moving it deeper in the forest as well. Even when the provision of food has stopped one should always go back to it and once in a while put one or two favourite food items in it so to keep the animal in the area it is in.

Acknowledgements

We thank Mrs. Pornpen Payakaporn, Secretary of the Wild Animal Rescue Foundation of Thailand and Mr. Preecha Sonserm, Director of the Gibbon Rehabilitation Project, for generous cooperation, Mr. Wattana Nitikun, Chief of the Khao Phra Theaw Non-hunting Area, for his hospitality, volunteers and Thai staff in the Gibbon Rehabilitation Project, for collect data and follow up the gibbon after release.

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