The Tapanuli orangutan is a critically endangered species of orangutan that can be found only in South Tapanuli in the island of Sumatra in Indonesia. It is one of three known species of orangutan, alongside the Sumatran orangutan, found farther northwest on the island, and Bornean orangutang. Tapanuli orangutans resemble Sumatran orangutans more than Bornean orangutans in body build and fur color. However, they have frizzier hair, smaller heads, and flatter and wide faces. Dominant males have prominent mustaches and large flat cheek pads, known as flanges, covered in downy hair. Both male and female Tapanuli orangutans have beards and as with the other two orangutan species, males are larger than females.
Tapanuli orangutans are exclusively arboreal and spend most of their time high up in the trees. This is probably due to the presence of Sumatran tigers in the area. They lead a solitary life and can be seen in pairs only when a mother is raising her young. Tapanuli orangutans are active during the day moving slowly in search of food through the trees. At night, they build a nest for sleeping up high in the canopy out of folded branches. Orangutans communicate with various sounds. Males will make long calls, both to attract females and to advertise themselves to other males. Both sexes will try to intimidate conspecifics with a series of low guttural noises known collectively as the "rolling call". When annoyed, an orangutan will suck in air through pursed lips, making a kissing sound known as the "kiss squeak". Mothers produce throat scrapes to keep in contact with their offspring. Infants make soft hoots when distressed. Orangutans are also known to produce smacks or blow raspberries when making a nest.
Tapanuli orangutans are omnivores. They have a unique diet that contains unusual items like caterpillars and conifer cones. They also consume fruits such as figs, mangoes, lychees, durian, and other plants.
After a gestation period that lasts for 9 months, female Tapanuli orangutans give birth to a single infant. The young clings to its mother for safety and remains at her side during the first few years. Infants usually stay with their mother until the age of 7 years, while being taught special skills for forest survival. Along with other orangutang species, Tapanuli orangutans are one of the most slowly-maturing animals in the world, with females bearing a maximum of three infants during their lifetime. Females become reproductively mature by the age of 12-15 years and males at an average of 15-20 years old.
Tapanuli orangutans are classified as critically endangered because of hunting, conflict with humans, the illegal wildlife trade, rampant habitat destruction for small-scale agriculture, mining and a proposed hydroelectric dam, the Batang Toru hydropower project, in the area with the highest density of orangutans, which could impact up to 10% of its already dwindling habitat and degrade important wildlife corridors. If the necessary conservation measures and practices are not implemented conservationists predict an 83% decline in three generations (75 years). This means that Tapanuli orangutangs could be extinct from the wild in the very near future.
According to the IUCN Red List, the total population size of Tapanuli orangutangs is fewer than 800 individuals. Currently, this species is classified as Critically Endangered (CR) on the IUCN Red List and its numbers today are decreasing.