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The habitat analysis was carried out to ensure that the island was …

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- Wildlife reintroduction: considerations of habitat quality at the release site

The release site is an island of 100 ha situated on the Kapuas River, 75.4 m south of Palangka Raya on the road to Banjarmasin in Central Kalimantan, Indonesian Borneo (Figure 1), known as Pulau Mintin (02° 50' N, 114° 12' E, Figure 2).

It is lowland freshwater swamp forest (FWS) at an altitude ranging from 10 to 22 m a.s.l. and is frequently flooded by the seasonal rains (the surrounding area is a floodplain), making the floor unsuitable for the gibbons and encouraging them to remain in the treetops. The island is 100 ha of regenerating secondary forest in the Kapuas River. This island is also home to wild Nasalis larvatus (group size 8), Macaca nemestrina (group size 9–13), M. fascicularis (group size 5–10) and several hornbills (exact numbers unavailable). The macaques and proboscis monkeys were not observed on the island continuously and were seen to swim between the island and the mainland (a distance of about 200 m). There are no large carnivorous predators on the island though crocodiles were seen in the interior of the island during the wet season. There are reports of large snakes on the island though the author did not encounter any during this study. The purpose of this paper is to highlight the need to assess habitat suitability and quality before any release takes place, and to stress the need for ongoing monitoring of habitat quality post-release. To assess the feeding competition between reintroduced gibbons and other species, data are needed on food competition, feeding rates and food intake. These data form the post-release monitoring phase and can only take place once an area has been deemed suitable for reintroducing gibbons. Feeding competition data are not available as the macaques were not habituated. Analysis of the activity budgets of the released gibbons shows them to be spending 37% of their time feeding. This figure is equivalent to other studies of wild agile gibbons [23,24].

The local community were accustomed to hunting and logging the island and many logging skids are still present. Following negotiations with local chiefs and elders the local people have agreed to stop logging and hunting on the island and are actively protecting it, in collaboration with the local police.

To determine the suitability of the habitat for the pair of Kalaweit gibbons it was necessary to establish the fruit abundance and productivity of the release area, Mintin Island. From September 2002-December 2003 a preliminary survey of known fruiting trees on the release island that were eaten by macaques and/or gibbons was carried out by the local people of Mintin Village, based on their knowledge of fruiting trees on the island. This initial survey gave local names only. With the assistance of a botanist from Palangka Raya University, SMC collected samples of all fruiting trees for which the Indonesian or scientific names could not be identified through local name alone. Scientific identification was made by Erna Shinta, resident botanist at CIMTROP (Centre for International Co-operation in Management of Tropical Peatlands) at Palangka Raya University. Trails were not cut on the release island, nor were transects, but every fruit-producing tree was counted in the initial survey by dividing the island into three block (based on average canopy height). The island is 100 ha and subsequent surveys noted the number of marked trees that were producing fruit for each species in each block. This number was then extrapolated using the list of total tree numbers to obtain abundance.

In the initial floristic survey circa 6000 trees were examined. Fruit-producing trees >10 cm Dbh were marked during the initial habitat survey. Due to past logging, the number of large trees (>20 Dbh) were fewer then would be found in pristine forest. All fruit trees on the island were counted and identified and density calculated (Table 1). Fruit trees identified as the most important for gibbons (Table 2) and >10 cm Dbh (diameter at breast height) on Mintin Island were surveyed twice a month (for one year). The number of genera that were producing young leaves, flowers and ripe fruit. Trees were scored for fruiting or not, presence of flowers or young leaves. Based on the proportion of those producing fruit each month from each species, a value for overall productivity for that species was extrapolated.

Authors' contributions

SMC conceived of the study and carried out the behaviour and ecological habitat analysis for this research.


SMC would like to thank Aurelién Brulé (Chanee), the director of the Kalaweit Project, and all staff who helped with data collection. Also to LIPI, the Indonesian Institute of Science for permission to work in Kalimantan. Funding was provided by The Gibbon Foundation, the C.K. Marr Educational Trust and Downing College, Cambridge.

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