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.