Page 120 - Present Day Wildlife_Float

Orangutans are classified as great apes. There are three extant species in the genus Pongo*,
which is the only surviving species of the subfamily Ponginae in the family Hominidae. Orangutans
are found only in parts of Borneo and Sumatra. The average height of a fully grown adult is around
1.3 metres and a weight of around 75 to 130kg.

*Genus Pongo
Bornean orangutan (Pongo pygmaeus)
Sumatran orangutan (Pongo abelii – Sumatra
northwest of Lake Toba)
Tapanuli orangutan (Pongo tapanuliensis – Su-
matra south of Lake Toba)

The orangutans have dark grey skin with a
partially covering coat of long reddish hair. In
youth the coat is bright orange, but darkens as it
matures, to a purple like red or chocolate colour.
Their backs, chest and hands are usually bare and
their face though bare can develop hair giving
them a beard. They have small sunken eyes a
small nose and small lobe-less ears. They have a
unique arm span of around 2 metres – longer than
their body – and when their arms are fully extend-
ed their long hairy coat forms a kind of cape. Their
hands have four long fingers and a thumb that al-
lows them, just like the human hand, to grip
branches and manipulate objects. Remarkably, their thin feet, which have four long toes and a toe
like thumb, have the same potential. Orangutans do not have tails instead they use their feet to grip
and hang from branches freeing up their hands to pick food. They also use their feet to hold and eat
food. All Orangutans start life much the same, with a round head and face, but as they mature, this
all changes, those with a high testosterone level will develop flaps on both sides of their face, known
as flanges – females find large flanges attractive. Those adults with low testosterone levels will not
have flanges and are known as ‘unflanged’ and tend to be slightly slimmer and smaller in build. The
reason why this difference in testosterone levels occurs is unknown, though, there are many theo-
ries. There are however, other differences across the three species. The two Sumatran species have
longer faces, are thinner with lighter and longer hair than the Bornean orangutan, while the Ta-
panuli orangutan has shaggier hair, a smaller skull, and flatter face than the Bornean and Sumatran
orangutans.

Orangutans are arboreal and in the wild are forest dwellers and rarely leave the trees. They
are solitary animals, but do come together at mating times, when males will fight with one another
for mating supremacy, usually with the females present. However, unlike other primates who use
social grooming as a bonding tool, orangutans in groups are never seen grooming one another.
They are an intelligent species and have learned to use long sticks to pry termites and ants out of
their nests in trees. They spend most of the day feeding and resting, then at night build an elaborate
sleeping nest out of branches and leaves. Communicating with others is done through a series of
sounds and expressions, like beckoning, and stomping. Adults have a throat pouch that can send
long bellowing roars that can be heard over 2 km away. Oftentimes, males use these calls to attract
a mate or a threatening gesture aimed at other males. Other close contact sounds are made usually
between mating couples or parent and young, like pursed lip hissing, grunting or rumbling sounds.

Orangutans are Frugivores, and will eat plant roots, shoots, nuts, seeds and most fruit avail-
able to them in their environment. They are also known to eat bark, insects and birds eggs, possibly
to get the minerals missing from their frugivorous diet. They will even leave the trees for a short
time to consume small quantities of soil usually found on the roots they unearth and to lick rocks
rich in minerals. On land Orangutans are very slow, they move around on all fours but are not, like
most primates, fist or knuckle walkers, they walk on their palms. This makes walking, slow and
awkward, making them vulnerable to fast moving predators like, tigers, leopards, crocodiles and
wild dogs.