Orangutans


Tim Sanderson
Anth 111

In Malay orang means "person" and utan is defined as "forest\'. Thus
Orangutan literally means "Person of the Forest". Orangutans are found in the
tropical forests of Sumatra and Borneo. They are the most arboreal of the great
apes and move amongst the safety of the trees from one feeding site to the next.
They are so well adapted to arboreal life that they cannot place their feet on
the ground, instead they walk on the outside of their curved foot.
There is a scattered population of orangutan in Indonesian Borneo,
Malaysia Borneo and northern Sumatra. The different habitats have isolated the
orangutan reproductively and geographically from one another creating a "degree
of difference" or two subspecies. There are several different characteristics
between the two subspecies of orangutans and it has recently been suggested that
they may be a separate species. The Borneo male has relatively large cheek
pads, a tremendous laryngeal sac and a square shaped face. The Sumatran male
has small pads and laryngeal sac, a ginger coloured moustache, a pronounced
beard, and a diamond shaped face. Individuals can also be distinguished
chromosomally, biochemically, and by their cranial characteristics.
There is a great deal of individual variety in the orangutan. "Each
orang-utan had a distinct personality and in dealing with such highly
intelligent animals in captivity, the keeper\'s knowledge of the individual was
probably more important than the knowledge of the overall behaviour patterns "
(Markham, 1980). Orangutan males, however, appear to be totally intolerant of
one another, especially the Borneo males who are even aggressive towards females
and infants. Male orangutans\' participation in social groups is limited to
sexual "consortship" with females. However, the Sumatran males tend to stay with
females for a longer period of time usually until the birth of the infant.
They may stay longer with their partner because of the presence of large
predators absent in the Borneo habitat. The orangutan has a menstrual cycle of
29-30 days, menstruation lasting 3-4 days. The Gestation period lasts slightly
less than nine months. Offspring pass through three stages, infancy (0-4),
juvenile (4-7), and adolescents (7-10). Mother young relationship lasts for a
long time, the young usually stay with their mother until they are mature.
Female Orangutans are not sexually mature or fully grown until the age of twelve
and will not have their first offspring until they are at least fourteen. Males
become sexually mature and fully grown at the age of fifteen. The cheek flanges
of the male easily recognize the differences between adults and semi-adults. The
flanges in the Boreal male curve out ward from the face and develop around the
age of eight and are not completely grown until the age of fifteen. Sumatra
flange development begins at the age of ten and is not complete until the early
twenties. The flange in the Sumatra orangutan lie flat against the face and
give a wide facial appearance especially in the mid facial region. The life
expectancy of orangutans in the wild is not known, but captive orangutans have
been known to live up to fifty years.
Orangutans are sexually dimorphic. Males are approximately twice the
size of females and weigh about 220 lbs. and reach a height of five feet. It is
believed that the males larger size may be an adaptation for mating because
there is strong competition among males for females. The pendulous laryngeal
sac, when inflated, increases the tone of the animals voice, producing "long
calls". In both subspecies (Borneo and Sumatran) calling acts as " a spacing
mechanism between the males and also advertise the location of the highest
ranking male to the mature females." (Rijksen,1978). The long call of the Borneo
male is long and drawn out where as the Sumatran is much shorter and has a
faster tempo. The difference may be attributed to the larger throat pouch the
Borneo has. The reason for the different calls is unclear. They may be related
to the terrain each subspecies inhabits. The faster call of the Sumatran may be
more effective in the rugged, mountainous terrain. The longer call of the
Borneo may be due to the wide distribution of this race.
A large portion of an orangutans day is spent looking for and consuming
food. Their diet primarily consists of fruit but they also eat leaves, bark,
flowers, insects, and birds eggs. One of their preferred foods is the fruit off
of the durian tree, it is supposed to taste like sweet garlic. After they have
finished eating and bedtime comes around the orangutans build themselves a new
nest forty to