Siamangs (Symphalangus syndactylus) belong to the family
of gibbons (Hylobatidae) or small apes and represent one out of four
genera within this group. They represent the most ancient branch within
the Hominoidea, since they split approximately 18 years ago from the
line leading to the great apes.
The division and phylogeny of the different species of small apes
is still discussed, but to date there are at least 12 different species
all restricted to the tropical rainforest of Southeast Asia.
are the largest species of small apes and are the only representatives
of this group that live sympatrically with other gibbon species (Hylobates
agilis, Hylobates lar) throughout their whole range of distribution.
With an approximate weight between 9–12 kg there are twice as
heavy as other gibbon species. Both sexes are black and have a laryngeal
air sac that is inflated during the production of their species-specific,
complex duet songs.
Although many gibbon species are close to extinction, siamangs seem
to represent a stable population, with an estimate of approximately
360,000 individuals (MacKinnon, 1987). However, there are no recent
surveys on the siamang population, with the exception of some studies
restricted to certain areas such as the Bukit Barisan Selatan National
Park (O'Brian et al., 2004).
Distribution and ecology
Siamangs are restricted to the tropical mountain forest on the island
of Sumatra and the peninsular Malaysia preferring altitudes between
700-900 m. Due to their arboreal lifestyle, siamangs inhabit the canopy
between 20 - 40 meters and almost never enter the ground. Siamangs spent
55% of their daily activity with foraging, 29% with resting and 16%
with traveling. They are often considered as a folivorious species because
their diet consists of a higher proportion of leaves in comparison to
other gibbon species.
Social structure and behaviour
Siamangs live in monogamous social groups consisting of an adult pair
and its one to three offspring born with an interval between two and
three years. There is virtually no sexual dimorphism and no differentiated
“role behavior” between the adult male and female. The group
life is characterized by a strong bonding between the family members
that spend most of their time in close proximity.
Each siamang family inhabits a particular home range with a size between
15 and 35 ha, whereof about 75% are defended as territory against other
siamang groups. A probable function in this regard is attributed to
the complex duett songs of siamangs that are mostly uttered in the early
morning hours. Maturing offspring is forced to emigrate and form a new
group after the corresponding pair partner is found.
- Use of gestures and facial expressions in siamangs and great apes
- “Towards a ‘grammar’ of gesture”: Comparison
of gestural communication of nonhuman and human primates — in
collaboration with Cornelia Müller, Ellen Fricke (European University
Viadrina, Frankfurt/Oder) and Hedda Lausberg
- Linear and simultaneous structures in gesture use of great apes
- Ontogeny of gestural communication in great apes
- Socio-cognitive skills of gibbons — in collaboration with
Juliane Kaminski, Max Planck Institute for Evolutionary Anthropology