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a great many small isolated populations. On the basis of the small population size and reduction of habitat, the species
is considered Critically Endangered by the IUCN Red List (Anon, 2004b).
Agile Gibbon H. agilis: This species occurs throughout Sumatra, apart from the northernmost part (roughly north of
Lake Toba) where it is replaced by the White-handed Gibbon. Outside Sumatra, it occurs in a small area on the Thai-
Malayan Peninsula. Like the Javan Gibbon, it is most abundant in lowland forest, although it does occur up to c. 1500
m asl. Forest destruction on Sumatra has not yet reached the same level as it has on Java or Bali. In recent years,
however, the area of (especially) lowland forest has seen a dramatic reduction largely due to illegal logging (Whitten et
al., 2000). Consequently, populations of Agile Gibbons in these habitats must have seen an equal reduction, although
little data are available. Populations in the more mountainous parts of the island seem to be more secure, but, as with
the Javan Gibbon, densities at these altitudes are considerably lower. At present, the Agile Gibbon is listed as Lower
Risk / near threatened by the IUCN Red List (Anon, 2004b).
Bornean White-bearded Gibbon H. albibarbis: Formerly generally considered a subspecies of the Agile Gibbon,
consistent differences in morphological (Groves, 2001), vocal (Geissmann, 1995) and genetic characters (Garza &
Woodruff, 1992) clearly suggest the Bornean White-bearded Gibbon represents a unique evolutionary unit. The species
is endemic to the south-western quarter of Borneo where it is found in the area south of the Kapuas River and west of
the Barito River. In comparison with other gibbons, a relatively large part of the distribution range of the Bornean Whitebearded
Gibbon is still forested. The majority of this is, however, handed out as logging concessions, bringing the
species in ever-closer contact with humans. Especially in the interior of Borneo, hunting of White-bearded Gibbons
poses a serious threat to the survival of the species (see also the account for Müller’s gibbon). The species has not yet
been assigned to a particular threat category by the IUCN Red List (2004) as the species is included as a subspecies of
the Agile Gibbon.
Credit: Julia Ng/TRAFFIC Southeast Asia
Müller’s Gibbon H. muelleri: Müller’s Gibbon is endemic to
the island of Borneo where it occurs north of the Kapuas River
and east of the Barito River, and as such, has been recorded in
Sarawak, Sabah, Brunei, East and South Kalimantan, and small
parts of West Kalimantan. The remainder of the island is
inhabited by the endemic Bornean White-bearded Gibbon. As
with the latter species, Müller’s Gibbon is mostly threatened by
habitat destruction. Although the total area of forest on Borneo
is still large compared to other parts of the distribution range of
gibbons, every year vast areas are cleared for timber production,
transmigration or agriculture and are increasingly lost due to
arson (e.g., Rijksen & Meijaard, 1999). Numbers of Bornean
Gibbons are declining overall because of habitat disturbance or
habitat alteration, and populations in some areas have been
greatly reduced or even eliminated by hunting. Borneo's interior
is inhabited, by and large, by the Dayak and the Penan / Punan
tribes and all animals larger than a rat (hence including all
Müller’s Gibbon Hylobates muelleri
species of primate) are hunted by these tribes (Caldecot, 1988,
1992). Local gibbon populations are easily exterminated by
hunting because of the species' loud songs, which attract attention; monogamy, which easily disrupts breeding; and
strong sedentary behaviour, which renders both evasion of hunters and rapid re-colonization of depopulated areas more
difficult (Bennett et al., 1987). At present, the Muller Gibbon is listed as Lower Risk / near threatened by the IUCN Red
List (Anon, 2004b).
IN FULL SWING:ASSESSMENT OF TRADE IN ORANGUTANS AND GIBBONS ON JAVA AND BALI,INDONESIA 5