Lonely Fruit Lovers
Orangutans live in the lowland rainforests of Sumatra and Borneo. Mother and infant as well as solitary adult males spend their entire life in the tree canopies.
Orangutans live in pristine primary lowland rainforests. On Borneo they are only found up to around 500m above sea level, but on Sumatra they can still be found up to 1000m asl or slightly higher. Sumatran orangutans spend almost their entire life off the ground in the rainforest canopy, where they find food, shelter and a place to sleep.
Typically only 1 or 2 adult orangutans share a square kilometer of forest, but this figure can be much higher, as much as 8 or more in some of the more productive habitats, such as the coastal peat swamps of Aceh Province in northern Sumatra.
Orangutans are often referred to as a near solitary species, with mother and infants being the most common grouping encountered. However, especially in Sumatra, bigger groups are also often found, especially groups of several mothers and their offspring, and especially when forest fruit is in plentiful supply. The orangutan's diet consists primarily of fruit (60%), but they also eat young leaves, insects such as ants and termites, and the underside (cambium) of tree bark. In Sumatra they will even catch and eat slow loris, a small and elusive nocturnal primate, whenever they come across them in the trees. This behaviour has never been seen on neighbouring Borneo.
Long living, but slowly reproducing
Female orangutans give birth to their first infant when they are about
15 years of age. The mother teaches everything to her single infant,
such as what to eat, where and when to find it in the forest, how to
build a comfortable nest and how to make and use tools. In order to
learn all these things young orangutans must stay with their mothers
for a long time and it is only when they are around 9 or 10 years old
that they start to spend significant amounts of time away from her,
exploring the forests on their own. Since they do have to teach their
infants so much, adult females reproduce only every 8 or 9 years. This
is the longest interbirth interval of any land living mammal in the
world! Orangutan mothers also almost always have only one infant at a
time. Twins do occur, but are very rare and probably at least one will
not survive as the mother needs both hands and both feet to travel and
feed in the treetops
As a result of long-term research projects
studying orangutans we now know they regularly live to be over 50 years
in the wild, but given their very slow reproductive rate, this means
that most females probably only have 4 or 5 infants in their lifetime.
This means that even a small amount of hunting or killing of females
and their infants has serious implications for a population's survival
in the long run.