The orangutan has the slowest development of adulthood in the world, and a lifespan of up to 60 years in the wild. Orangutang mothers also have the longest interval between offspring in the world (around 7 years), which contributes to the highest offspring survival rate of all great apes. The rather solitary adult life makes the long childhood essential in learning everything needed to survive and thrive in the rainforest for many years to come. Furthermore, the female orangutans apparently continue to be reproductive their whole life.
The beginning of new life - mating
When a female orangutan is between the age of 11 and 18 years it is time to have her first offspring. The females is usually made aware of the dominating males whereabouts by their categoristic “long call”, which can be heard from miles away. While mating, the male stays with the female for a few days to be sure that she is fertilized, with other less dominating (unflanged) males lurking nearby, searching for a quick opportunity to mate. After the mating sessions are over the male(s) leaves the female to raise their offspring on her own.
The orangutan baby is born 8 ½ months after a successful mating, weighing around 3 ½ pounds. They stay in physical contact with their mother at all times during the first months, clinging onto her body as she moves through the forest canopy while doing her daily activities. As the youngsters reach two years of age, the mothers start encouraging them to explore the treetops on their own. The baby orangutan typically suckles from its mother until it is three to four years old. During these first years the offspring receives crucial knowledge from the mother on how to survive in the forest on its own. It learns where to find food, what to eat, how to build sleeping nests, how to orientate in the forest and how to avoid natural enemies. Even when young orangutans have been weaned and are too big to be carried around, they still remain close to their mother, traveling, eating, and resting together until they are up to 8 years old.
Read more about physiology of the orangutan here >>
The orangutan is the only primate species with two different forms of mature males (bimaturism): Flanged males are distinguished by being twice the size of females, making so-called “long calls”, being aggressive towards other orangutan’s and having longer and darker hair with a facial desk. Unflanged males are characterized by being smaller, less dominant, more social and unaggressive towards other orangutans. It is usually in its teens that an orangutan male develops into a flanged male by evolving distinctive cheek pads - protruding fat folds in the face - thereby making them popular among females (the bigger the better). The cheek pads keeps growing the most of its life and acts like a microphone, extending the reach of its call. However, some male orangutans do not go through this transition face (unflanged males), and it has been suggested that unflanged males evolve large cheek pads when older flanged males move away or die. Thereby repressing its dominating appearance and behaviour until it is needed.
Life as a (flanged) male
Flanged males live a solitary life, only encountering conspecifics for mating purposes. Their home ranges in size from 100 to 1500 ha, overlapping the home range of multiple females. The flanged males avoid other males, and use “the long call”, which can be transmitted up to several kilometres, to keep out of each other's way. The long call also attracts fertile females, and when encountering a fertile female several males might fight for the right to mate with her.
Female orangutans are much more social than their sexual counterparts, and usually have one or more female offsprings in close proximity. Their home range is also smaller than males and more stable, ranging between 50 to 600 ha in size. The long childhood of their offspring, and their own interbirth interval of around 7 years (the longest in the world), makes female orangutans almost constantly finding themselves raising or educating younger family members. Through a whole life a female orangutan can generally expect to produce three to four new members of the orangutan family.