Life span: >40 years (captive)
Total population: 200,000 (Sumatra)
Regions: Malay Peninsula, Sumatra
Gestation: 210 days (7 months)
Height: 73.7 to 88.9 cm (M & F)
Weight: 11.9 kg (M), 10.7 kg (F)
Species: S. syndactylus
Subspecies: S. s. syndactylus, S. s. continentis
Other names: Hylobates (Symphalangus) syndactylus,
siamang, greater gibbon; S. s. syndactylus: Sumatran siamang; S. s.
continentis: Malaysian siamang.
The taxonomic arrangement of siamangs has been modified by Groves (2005) and
Mootnick & Groves (2005) who elevated the former subgenus Symphalangus to
full generic level where it was formerly a subgenus of Hylobates.
Photo: Roy Fontaine
Among the gibbons, the stocky siamangs are the largest (Mootnick 2006). The
pelage is glossy black, the upper body has long hair and the chest is broad
(Marshall & Sugardjito 1986; Mootnick 2006). The crown is flat and a white
brow-band occurs at low levels (<5%) in captive and museum examples (Geissmann
1993; 2003). Perhaps the most characteristic feature of the siamang is its
large inflatable throat sac, which is sparsely haired (Schultz 1933; Marshall &
Sugardjito 1986; Mootnick 2006; A.Mootnick pers. comm.). When fully
inflated, the throat sac is comparable in size to the animal's head (Papaioannou
1973). Siamangs have no tail, as is the case in all of the
lesser, or small, apes
(Ankel-Simons 2000). However, males possess a downward directed genital tassel
which can be as long as 13.5 cm (5.3 in) and resembles a tail (Marshall &
Sugardjito 1986; Mootnick 2006). It is difficult to visibly tell the subspecies
apart, although preliminary observations suggest that this might be possible
based on nose morphology (Mootnick 2006). The second and third toes are
connected by webbing which is variable in its extent, a condition that is
reflected in the species' scientific name (Schultz 1933; Marshall &
Sugardjito 1986; Mootnick 2006). In addition, sometimes the fourth and fifth
toes are also webbed (A. Mootnick & L. Theisen-Watt pers. obs. cited in Mootnick
There is some sexual dimorphism in siamangs, with males being somewhat larger
than females (Wilson & Wilson 1976). In a small wild-shot sample, adult
males averaged 11.9 kg (26.2 lb) and adult females averaged 10.7 kg (23.6 lb)
(Geissmann 1993). In a much larger survey of captive individuals, adult males
averaged 12.8 kg (28.2 lb) and adult females averaged 10.5 kg (23.1 lb)
(Orgeldinger 1994). Head and body length ranges between 29 and 35 inches (73.7
and 88.9 cm) (Chivers 1985).
The predominant type of siamang locomotion is its characteristic brachiation,
comprising around 80% of its movement (Chivers 1972b cited in Andrews &
Groves 1976). This type of locomotion is extremely advantageous in the complex
canopy environment for which the species is adapted (Bertram 2004). Other types
of locomotion include vertical climbing, swinging, jumping and arboreal bipedal
walking (Chivers 1972b cited in Andrews & Groves 1976; Papaioannou 1973).
When compared to other gibbons, siamangs are slower in their movement and they
rest by propping or draping themselves in the trees (Chivers 1972a).
In captivity, siamangs can live into their forties (Schmidt & Weigl 1999;
CURRENT RANGE MAPS (IUCN REDLIST):Symphalangus syndactylus
Siamangs are found on the island of Sumatra (Indonesia) and on the Malay
(Malaysia and Thailand) peninsula (Treesucon 1997; Mootnick 2006). Each of the
two locations has its own subspecies, with S. s. syndactylus being confined to
Sumatra and S. s. continentis confined to the northwest and central Malay
Peninsula (Mootnick 2006). Within the Malay peninsula, S. s. continentis is
restricted in the east by the Pahang River, in the south by the Maur river and
Tasek Bera, and in the north by the Perak river (Chivers 1980). There are no
reports of occurrence east of the central range of the peninsula (Groves 1972).
There is at least one report of siamangs from extreme southern Thailand, very
near the border with Malaysia on the Malay peninsula in the Narathiwat Province
(Treesucon 1997). On Sumatra, S. s. syndactylus occurs over most of the island
but is mainly found in the west (MacKinnon 1984; Jenkins 1990).
The tropical hill forest is the primary habitat of the siamang. The species
is most often found above 300 m (984.3 ft) in altitude, but can also live in
lowland forests (Chivers 1977). In addition to primary lowland and hill
forests, siamangs can also live in selectively logged primary freshwater swamp
forests, selectively logged lowland forests, selectively logged hill forests and
primary submontane forest (Wilson & Wilson 1976). Although sympatric with
other gibbons in some habitats, siamangs occur more often at higher elevations
than other gibbons (Wilson & Wilson 1976). However, the species is not
commonly seen above 1500 m (4921.3 ft), although it may
range as high as 1828.8 m (6000 ft) (Medway 1972; Caldecott 1980).
The seasons are not usually distinct in the tropical areas where the siamang
lives (Chivers 1974). In southwestern Sumatra, in the Bukit Barisan Selatan
National Park, rainfall is only weakly seasonal. Annually, it can be between
300 and 400 cm (118.1 and 157.5 in), amounts which are sometimes lower due to
severe droughts. At this site, annual temperatures are usually between 22 and
35°C (71.6 and 95°F) but can be as high as 40°C (104°F) (O'Brien
et al. 2003; 2004). On the Malay Peninsula, there is a time of increased
rainfall around the beginning of each year with a following drier season which
is accompanied by warmer temperatures. However, this cycle is variable between
years (Chivers 1974). At the study site of Kuala Lompat, in the Krau Game
Reserve in the Malay Peninsula during a two-year period, temperatures varied
between 16.1 and 33.3°C (61 and 92°F). The wet season lasted roughly
November-January, and the dry season between January-April (Chivers 1974).
On average, among several study sites in both Malaysia and Indonesia,
siamangs eat a variety of foods, including 49% fruit (between 32-61% of the
diet), 38% leaves (17-58%), 3% flowers (1-9%), and 10% insects (1-21%)
(Papaioannou 1973; Chivers 1974; Raemaekers 1979; MacKinnon & MacKinnon
1980; Palombit 1992; 1997; Bartlett 2007). Of the fruit, figs can make up a
significant percentage, up to 37% of the entire siamang diet (Bartlett 2007).
Siamangs also have a preference of leaf types, eating mostly young leaves and
only small amounts of mature leaves (Chivers 1974; Raemaekers 1979; MacKinnon
& MacKinnon 1980; Palombit 1992). Overall, more than 160 different species
of plant are eaten (T. O'Brien unpubl. data cited in O'Brien et al. 2003).
Photo: Alan Mootnick
The daily activity period is usually over ten hours long (Chivers 1974;
Raemaekers 1979). In general, siamangs awake around dawn and communally
defecate shortly thereafter (Papaioannou 1973; Chivers 1974; Chivers et al.
1975). They will then feed or rest, depending on their proximity to food
resources (Chivers 1972a). As to the daily pattern of activity, peaks in
feeding occur over the course of the morning and decrease after that for the
rest of the day (Papaioannou 1973; Chivers 1977). Resting increases over the
day to a peak in the afternoon, and travel peaks in the morning (Chivers 1974).
At night, siamang groups enter the highest branches of a single tree, high above
the canopy but sometimes lower and in several trees (Chivers 1974; Gittins &
Raemaekers 1980). Sleeping trees are often reused (Chivers 1974).
Daily time budgets vary between study sites, but traveling, resting and
feeding typically are predominant activities (Lappan 2005). In Sumatra, male
siamangs spend their time feeding (34.0%), resting (36.8%), traveling (16.8%),
in social activities (5.2%) and in other activities (7.3%). Female siamangs
spend their time feeding (37.3%), resting (33.8%), traveling (16.9%), in social
activities (5.4%) and in other activities (7.3%) (Lappan 2005). Elsewhere in
Sumatra during a different study, siamangs spent their time resting (44%),
feeding and foraging (40%), traveling (12%), in intergroup interactions (3%) and
singing (1%) (Palombit 1992; 1997). On the Malay peninsula, the day is spent
feeding (50%), resting (25%), and traveling (22%), with grooming, singing and
play each taking up about 1% of the day (Gittins & Raemaekers 1980). Among
the group, there is a coordination of activities. In one study, all members of
a group participated in the same activity over 60-75% of the day (Chivers 1976).
Home ranges vary between 0.2 and 0.48 km² (0.08 and 0.19 mi²), with no or
little overlap (Papaioannou 1973; Chivers 1974; Raemaekers 1979; MacKinnon &
MacKinnon 1980; Raemaekers & Chivers 1980; Palombit 1996b; O'Brien et al.
2003). Average day ranges of siamang groups range between 640-1289 m (Chivers
1974; Raemaekers 1979; MacKinnon & MacKinnon 1980; Lappan 2005; Bartlett
2007). During wet months, daily travel is shorter than in dry months
(Raemaekers 1980). Siamangs spend most of their time high in the forest canopy,
over 24 meters (78.7 ft) above the ground, but will also descend to around 7.5
meters (24.6 ft) above the ground and rarely lower (MacKinnon & MacKinnon
1980). Arboreal group movements are usually in single-file through the same
pathway (Chivers 1974).
Siamangs live in sympatry with a number of other primates including the slow
loris (Nycticebus coucang),
long-tailed macaque (Macaca fascicularis),
pigtail macaque (Macaca nemestrina),
Thomas's langur (Presbytis thomasi),
lar gibbon (Hylobates lar),
agile gibbon (Hylobates agilis), banded langur
ebony langur (Trachypithecus auratus), Horsfield's
tarsier (Tarsius bancanus),
and Sumatran orangutan (Pongo abelii) (Palombit 1992;
Lappan 2005). In addition, in northern Sumatra, siamangs are sympatric with
orangutans and lar gibbons, the only
place in the world where three species of non-human apes coexist (Palombit
1996b). The siamang and other gibbons with which it is sympatric might compete
for food as in some cases there is diet overlap (Raemaekers 1984). This is the
case with the sympatric lar gibbon where infrequent
confrontations between siamangs and the species over food resources have been
observed (Raemaekers 1978). In addition, in at least one study, a male siamang
associated with a male lar gibbon and the pair
traveled, fed, and even chorused together (MacKinnon & MacKinnon 1977).
In general, predation on gibbons is not well documented, and in no field
study of either Hylobates sp. or Symphalangus syndactylus has direct predation
been observed (see Uhde & Sommer 2002). However, a full-sized siamang was
found in the digestive tract of a python (Schneider 1906 cited in Uhde &
Content last modified: May 20, 2008
Written by Kurt Gron. Reviewed by Alan Mootnick.
Cite this page as:
Gron KJ. 2008 May 20. Primate Factsheets: Siamang (Symphalangus syndactylus) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/siamang/taxon>. Accessed 2015 January 26.