Chapter 1
Introduction
© 1981 Markus Kappeler
1.1. Set of questions
The Javan silvery gibbon (Hylobates lar moloch) is
almost exclusively restricted to primary tropical rain forest
below approximately 1500 meters [KAPPELER, 1981].
This vegetation type, which shows a singularly large
biomass and is exceedingly high in species diversity, is inhabited
by a large number of animal forms of life; according to WHITMORE
[1975] the tropical lowland rain forest of South-East Asia contains
the most luxuriant and most complex ecosystems on earth.
The ecological niches are extremely manifold. Some
animal species are ecological specialists and, as such, are equipped
with niche-specific physiological, morphological and ethological
characteristics; others are generalists. Each species is limited
to certain factors of space and time and, accordingly, shows
particularities in the use of resources.
In this paper the silvery gibbon is investigated as
a component of the tropical rain forest of West Java. The following
subjects are treated:
- technique and style of locomotion,
- diet and feeding,
- avoidance of predators,
- female song bout,
- home range and territory.
Studies of intragroup social relations could not be
conducted because of the difficulties involved in observing the
animals in the wild.
H.l.moloch is the sixth member of
the Hylobatidae on whose way of life a study - based on long-term
field observation - is presented.
Detailed ecological and ethological
studies have already been carried out on H.l.carpenteri in North
Thailand [CARPENTER, 1940], H.l.lar in Malaysia [ELLEFSON,1967],
H.syndactylus in Malaysia [CHIVERS,1974], H.l.agilis in Malaysia
[GITTINS, 1979] and H.klossii in Indonesia [WHITTEN,1980].
Until now, H.l.moloch has not been
the subject of any investigation.
1.2. Study area
The data for this paper were collected from August
1975 to October 1976 in Ujung Kulon/Gunung Honje Nature Reserve
in West Java (Indonesia).
1.2.1. Nature Reserve Ujunq Kulon/Gunung Honje
Detailed descriptions of the Nature Reserve Ujung
Kulon/Gunung Honje have been given by SATMOKO [1961], SCHENKEL
& SCHENKEL-HuLLIGER [1969], HOOGERWERF [1970], HALDER [1976]
and BLOWER & VAN DER ZON [1977].
The reserve harbours Java's most westerly gibbon population
which is estimated at 400-1400 individuals [KAPPELER, 1981a].
The population inhabits the climax rain forest of
the Gunung Honje Range and its south-western spur extending into
the depression between the Javan main land and Ujung Kulon peninsula
(figure 1). The extent of high rain forest is approximately 100
sq.km. In the Gunung Honje area it is delimited by man-made clearings;
in the area of the flat isthmus, which is practically at sea-level,
the forest gives way to vegetation flourishing in brackish water.
Some few individuals - isolated from the rest of the
population - inhabit a small patch of high rain forest in the
south-east of the Ujung Kulon peninsula (Tereleng, 'E'; figure
1); the rest of the peninsula is not inhabited by gibbons [for
reasons s. KAPPELER, 1981a].
1.2.2. Turalak
Turalak ('T'; figure 1), within the Ujung Kulon/Gunung
Honje Nature Reserve, was chosen as the main study area. It lies
on the gentle slope of the Gunung Honje spur running south-west,
approximately 50 meters above sea-level.
The temperatures, measured at Turalak
in the shade at 25 meters above ground varied during the study
year between a minimum 21-26°C (night) and a maximum 25-30°C
(day).
Turalak was especially suitable for a long-term study
for the following reasons:
1. Vegetation. Turalak is covered with exceptionally
homogeneous primary tropical lowland rain forest and therefore
provides an optimum gibbon habitat [s. KAPPELER, 1981a].
A further advantage is that, in large areas of this
part of the forest, the lowest stratum consists of Arenga obtusifolia.
This palm largely inhibits the development of thick undergrowth
[s. SCHENKEL et al., 1978], so that walking in the forest is
quite easy.
2. Gibbon population. Corresponding to the good quality
of the forest, the density of the local gibbon population is
especially high.
The evaluation of «transects» [WILSON
& WILSON, 1975] of 5 km length, which were performed in a
north south direction through forest bordering the study area,
yielded an average gibbon density of 9 individuals/sq.km (n =
7). In the study area itself, 18 individuals lived in an area
of 0.8 sq.km, corresponding to a local density of 22 individuals/sq.km.
3. Topography. The terrain is very flat: the study
area is drained by a multitude of small rivulets and ditches,
separated from each other only by slight elevations; steep slopes
are not found. These conditions highly facilitate movement on
foot, allowing the gibbons to be followed and observed with comparative
ease.
4. Accomodation. Turalak is only a few minutes walk
from the guard post Kalejetan (figure 1); it was therefore not
necessary to build a special camp.
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