The Siamang (S ymphalangus
syndactylus) is a tailless, arboreal, black furred gibbon native to the
forests of Malaysia, Thailand, and Sumatra. The largest of the lesser
apes, the Siamang can be twice the size of other gibbons, reaching 1 m
in height, and weighing up to 14 kg. The Siamang is the only species in
the genus Symphalangus.
The Siamang is distinctive for two reasons. The first is that two
fingers on each hand are fused together hence the name "syndactylus",
from the Ancient Greek sun-, "united" + daktulos "finger". The second is
the large "gular sac" (found in both male and female of the species),
which is a throat pouch that can be inflated to the size of its head,
allowing the Siamang to make loud resonating calls or songs.
There may be two subspecies of the Siamang. If so, they are the
nominate Sumatran Siamang (S. s. syndactylus) and the Malaysian Siamang
(S. s. continentis, in peninsular Malaysia).[3] Otherwise, the Malaysian
individuals are only a population. The Siamang is the only gibbon which
occurs sympatrically with other gibbons; its two ranges are entirely
within the combined ranges of the Agile Gibbon and the Lar Gibbon.
Although the siamang is given a different name than other gibbons, this
division is not cladistically sound, since the genus Nomascus split from
the rest of the gibbons before Symphalangus split [4]
The Siamang can live up to 30+ years in captivity.
While the illegal pet trade takes a toll on wild populations, the
principal threat to the Siamang is habitat loss in both Malaysia and
Sumatra. Palm oil production is clearing large swathes of forest,
reducing the habitat of the Siamang, along with that of other species
such as the Sumatran Tiger.
The Siamang inhabits the forest remnants of Sumatra Island and the
Malay Peninsula, and is widely distributed from lowland forest to
montane forest, even a rainforest. And can be found at altitudes of up
to 3800 m . The Siamang lives in groups of up to 6 individuals (4
individuals on average) with a home range 23 hectares on average. Their
day ranges are substantially smaller than those of sympatric Hylobates
species, often less than 1 km. The Siamang's melodious choir singing
breaks the forest's silence in the early morning after the Agile Gibbon
or Lar Gibbon's calls. The Siamang in Sumatra and the Malay Peninsula
are similar in appearance, but there are some differences in behaviour
between the two populations.
Diet
The Siamang mainly eats various parts of plants. The Sumatran Siamang
is more frugivorous than its Malayan cousin, with fruit making up to 60%
of its diet. The Siamang eats at least 160 species of plants, from vines
to woody plants. Its major food is figs (Ficus spp.), a member of
Moraceae family.The Siamang prefers to eat ripe fruit rather than unripe
fruit, and young leaves rather than old leaves. It eats flowers and a
few animals, mostly insects. When the Siamang eats large flowers, it
will eat only the corolla (petal), but it will eat all parts of smaller
flowers, with the small fruit collected in its hand before being
consumed. When it eats big and hard seeds or seeds with sharp edge it
will peel out the fruit flesh and throw away the seed.
Although its diet consists of substantial portions of fruit, it is the
most folivorous of all members of Hylobatidae. As it is also the largest
gibbon, and thus fits well with the general primate dietary trend in
which larger primates tend to be more folivorous
Demography and population
A group of Siamang normally consist of an adult dominant male, an
adult dominant female, with offspring, infant and sometimes a sub-adult.
The sub-adult usually leaves the group after the age 6 to 8 years;
sub-adult females tend to leave the group earlier than sub-adult males.
Siamang males tend to offer more paternal care than other members of the
family Hylobatidae, taking up a major role in carrying the infant after
it is about 8 months old . The infant typically returns to its mother to
sleep and nurse. A study in relation to effect of habitat disturbance on
the Siamang found that group composition is varied in age-sex structure
between intact forest and post-burnt forest. The post-burnt population
was more adult and sub-adults than the intact population. Post-burnt
groups contain fewer infants, small juveniles and large juveniles
compared to intact forest groups. Infant survival rates in post-burnt
groups are lower than in intact forests. The number of individuals in
intact forests is higher than in post-burnt forests.The Siamang in
disturbed forests live in small groups and have a density lower than in
intact forests because of lack of food resources and trees for living.
In the 1980s, the Indonesian population of the Siamang in the wild
was estimated to be 360,000 individuals.
This seems over-estimate today, as an example, Bukit Barisan Selatan
National Park (BBSNP) is the third largest protected area (3,568 kmē) in
Sumatra, of which approximately 2,570 kmē remains under forest cover
inhabit by 22,390 siamangs (in 2002 censuses). According to two
different research projects conducted in Sumatra, the Siamang prefer to
inhabit lowland forest below between 500 m in altitude and over 1000 m
above sea level.
Behavior
The Siamang tends to rest for more than 50% of its waking period
(from dawn to dusk), followed by feeding, moving, foraging and social
activities. It takes more rest during midday, taking time to groom each
other or play. During resting time it usually uses a branch of a large
tree lying on their back or on their stomach. Feeding behaviors,
foraging, and moving are most often in the morning and after resting
time.
In the dry season the length of the Siamang's daily range is longer
than in the rainy season. The Siamang in southern Sumatra undertakes
less foraging than the Siamang in other places because it eats more
fruit and therefore consumes more nutrition, which results in less time
needed for looking for food. Sometimes the Siamang will spend all of the
day in one big fruiting tree, just moving out when it wants to rest and
then coming back again to fruiting trees.
Role of calling
The Siamang starts its day by calling in the early morning and calls
less after midday, with the peak of their calls around 9:00 am to 10:00
am. Most of the Siamang's calls are directed to its neighbours rather
than to inside its home range. This means that the Siamang's calling is
in response to disturbances and is to defend its territory. Calls in the
late morning typically happen when it meets or sees another Siamang
group. The edge of the Siamang's home range, which may overlap another,
is often the places where calling is made. Counter-call (co-response
calling) occasionally happens near the border or in the overlap area.
Calls are numerous when fruit is more abundant rather than when fruit is
less available. Branch shaking, swinging, and moving around the tree
crowns accompany the calling. This movement might be to show the other
groups where they are.
The Siamang prefers calling in the living, high and big trees, it
might be the places where another group is easy to see. Beside that,
living, big, and tall trees can support Siamang movement. Calling trees
are usually near feeding trees but sometimes they call in the feeding
trees.
Siamang and their habitat
As a frugivorous animal, the Siamang disperses seeds through
defacation as it travels across its territory. The Siamang can carry
seed and defecate over 300 m with the shortest distance being 47.6 m
from the seed resource, which supports the forest regeneration and
succession.
Threats to population
The Siamang, as an arboreal primate, absolutely depends on the forest
for existence, needing trees for its living. At the moment, the Siamang
is facing a population decrease due to habitat loss, poaching and
hunting.
Habitat loss
A major threat to the Siamang is habitat loss due to plantation,
forest fire, illegal logging, encroachment, and human development.
Firstly, palm oil plantations have removed large areas of the Siamang's
habitat in the last four decades. Since 2002 107,000 square kilometres
of palm oil have been planted, which has replaced much rainforest in
Indonesia and Malaysia, where the Siamang originally used to live.
Secondly, in the last two decades, forest fire destroyed more than
20,000 kmē of Sumatran rainforest, mainly in the lowland area where most
of the Siamang live. Thirdly, the rate of illegal logging in Indonesia
increased from 1980 to 1995 and even more rapidly after the reformation
era beginning in 1998.These illegal activities devastated the remaining
tropical rainforest especially in Sumatra. Fourthly, forest
encroachments change forest cover into cultivated land, for example; the
rising price of coffee in 1998 has been encouraging people in Sumatra to
replace the forest with coffee plantation. Fifthly, development in many
areas needs infrastructure such as roads, which now divide a lot of
conservation areas have been caused forest fragmentation and edge
effects. Unfortunately, the Siamang as an arboreal primate faces
difficulty because road establishment has disconnected their pathways.
Poaching and hunting
Unlike other parts of Asia, primates are not hunted for their meat in
Indonesia (the exception is in Chinese restaurants in Indonesia which
sometimes serve macaque on their menu). However, they are poached and
hunted for the illegal pet trade, mostly for infant Siamang. Poachers
kill the mothers because mother Siamang are highly protective of their
infants. It is therefore very difficult to remove the infant without
first killing the mother. Despite the fact that most Siamang on the
market are infants many infants nevertheless die during transportation. |
