Orangutans are mostly covered with long, reddish-brown hair and grey-black skin. An orangutan has a large, bulky body, a thick neck, very long, strong arms, short, bowed legs, and a large head with a prominent mouth area. Though largely hairless, their faces can develop some hair in males, giving them a mustache.
Adult males have large cheek flaps to show their dominance to other males. Sumatran orangutans have lighter hair and a longer beard than their Bornean relatives, and Sumatran males have narrower cheekpads. Mature males’ throat pouches allow them to make loud long calls to attract females and intimidate rivals. The joint and tendon arrangement in orangutans’ hands is adapted to arboreal locomotion.
Flanged adult male orangutans can reach 175 cm (5.7 ft) in height and weigh over 118 kg (260 lb), while females can grow up to 127 cm (4.2 ft) and weigh around 45 kg (99 lb).
The Sumatran orangutan is endemic to the island of Sumatra, Indonesia
. Once far more widespread on the island, the species is now generally restricted to the north of the island, north of the Batang Toru river on the west coast of North Sumatra province. The Leuser Ecosystem, in the provinces of Aceh and North Sumatra, is considered to contain 91% of the remaining wild population. Whilst this is largely a mountainous area, orangutans exist in greater numbers and at higher densities in the remaining lowlands (regions below 1,000 m).
The Bornean orangutan is endemic to the island of Borneo where it is present in the Malaysian states of Sabah and Sarawak, as well as in Kalimantan (Indonesian Borneo). Species distribution is now highly patchy throughout the island: it is apparently absent or uncommon in the south-east of the island, as well as in the forests between the Rejang River in central Sarawak and the Padas River in western Sabah. Distribution for each subspecies is as follows.
The northeast Bornean orangutan is present in East Kalimantan and Sabah.
The northwest Bornean orangutan is present in north-western Kalimantan from north of the Kapuas River to north-eastern Sarawak.
The central Bornean orangutan is present in West Kalimantan south of the Kapuas River and Central Kalimantan west of the Barito River.
Male orangutans mature at around 15 years of age, by which time they have fully descended testicles and can reproduce. Females give birth to their first offspring at 14-15 years of age, after a gestation period of about 9 months. Intervals between births are 7 to 8 years, the longest birth intervals among the great apes, and a female has usually no more than 3 offspring in her lifetime. This means that orangutan populations grow very slowly, and take a long time to recover from habitat disturbance and hunting.
Raising the young is done mostly by the females, and infants remain dependent on their mothers for at least 5 years. Completely dependent on their mothers for the first 2 years of their lives, juvenile orangutans (2-5 years of age) increasingly move away from their mothers. Orangutans are usually weaned at about 4 years of age. An orangutan’s lifespan in the wild is about 35-40 years.