Gestation
Orangutan gestation (pregnancy) lasts around eight and a half months.
During pregnancy, females are vulnerable to droughts and other conditions affecting food supplies. If food is not plentiful, pregnant females may become weak.
Birthing
Generally, one infant is produced with each birth. Twins are rare.
Females usually give birth on their nests, which are often more than 30 m (99 ft.) up in the trees. These nests are carefully constructed to accommodate the pregnancy weight gain and to prevent the newborn from slipping through a crack.
Orangutan mothers are the infants’ only means of transport, support, food, comfort, safety, and often the exclusive source for information and essential learning experiences.
Infants & Young
Infant orangutans weigh about 1.5 kg (3.3 lb.) at birth (small enough to fit in a human's palm) and are completely dependent on their mother. Infants cannot even raise their heads at birth.
Once infants are born, mother orangutans clean them and begin nursing.
The legs and arms of the infants are very thin at birth. Their muscles begin to develop once they start climbing trees.
Infants have large eyes that are open at birth. They are sparsely covered with hair, have wrinkled faces, and are toothless.
Infant Development
Orangutans have the longest infant development period of all the great apes. It is commonly divided into three stages.
Infant (0-3 Years)
Soon after birth, infants learn to use their fingers to grip onto their mothers’ chests. An infant's grip is extremely firm, capable of supporting its own body weight with just their hands.
Two weeks following birth, infants usually have learned how to sit upright and use its hands.
Babies begin eating soft fruit, in addition to nursing, at around three months of age. Initially mothers help prepare the solid food by grinding it up with their teeth, then giving it to their young to chew.
Around two years of age, infants transition from hanging onto their mother's chest to riding on their backs.
Juvenile (3-7 Years)
Mothers begin to wean (transition from nursing to solid foods) their young as juveniles, around three to four years of age.
Increasing independence leads juveniles to sometimes travel alone.
Juveniles no longer share their mothers' night nests and begin building their own. The juveniles' nests remain close to their mothers and are often in the same tree.
At around four years of age, juveniles begin to climb and search for their own food.
Adolescent (7-10 Years)
Upon gaining independence from their mothers, adolescent orangutans will often travel widely before settling in a permanent home range. Males will travel further from their mother's home range than females, who often establish adjacent home ranges.
Female adolescents often stay with their mothers longer than males. If the mother has another baby, the female adolescent often helps her mother care for the infant, learning maternal behaviors.
Females are considered adults with the birth of their first infant. This usually takes place between 14 and 16 years of age. Males are considered adults with the emergence of cheek pads, a throat pouch, and a developed long call. This usually takes place as late as 19 or 20 years of age.
Birthing Intervals
With the high maternal investment in raising young, there is usually an eight to ten year time span between births.
Since females generally have only three to four offspring in their lifetime, males may engage in fierce competition for females.
As a slow reproducing animal, orangutans are particularly vulnerable to population losses, as they take decades, even centuries to replace.
Females remain fertile until about 30 years of age.
