One Earth’s “Species of the Week” series highlights an iconic species that represents the unique biogeography of each of the 185 bioregions of the Earth.
Course orange hair, lengthy limbs, a protruding coconut-like mouth, and expressively warm eyes, orangutans are one of the many great apes that have fascinated their human cousins. Splitting from other hominids like gorillas, chimpanzees, and humans between 19.3 to 15.7 million years ago, orangutans are now only found in the rainforests of Indonesia and Malaysia. There are three species of orangutans, the Bornean orangutan, native to the island of Borneo, the Tapanuli orangutan found only on South Tapanuli in the island of Sumatra, and just a bit farther northwest on the island is where the Sumatran orangutan calls home. Thinner faces with longer, paler, red-colored hair, Sumatran orangutans are crucial to this rainforest. More frugivorous than other orangutans, they are seed dispersers helping keep biodiversity flourishing.
Male Sumatran orangutans grow to an average of 1.7 m (5.6 ft) tall and 90 kg (200 lb), while females are slightly smaller, measuring 90 cm (3.0 ft) and 45 kg (99 lb). Despite their weight, these orangutans are almost exclusively arboreal, living among the trees. As the heaviest mammals to travel by tree, their locomotion is specialized by slow movement, long contact times, and an impressively large variety of postures in which they test the weight limits of branches. It is with this motion throughout the rainforest and their diet that Sumatran orangutans play an essential role in their ecosystem. Consuming fruits of all kinds, especially figs, jackfruits, and seeds of the Neesia tree, Sumatran orangutans help further grow the rainforest with their droppings.
In native Malay, the name ‘orangutan’ derives from orang meaning ‘people’ or ‘person’ and hutan meaning ‘forest.’ As “people of the forest,” Sumatran orangutans have been observed using a variety of tools. Using a stick to dig for termites is common as well as for poking a bees nest to catch honey. Crafted sticks are also used to open the Neesia fruit to avoid fiberglass-like hairs that are painful if eaten. Over time, Sumatran orangutans will collect entire "toolboxes" of useful sticks, twigs, and stones.
Another way in which Sumatran orangutans mirror humans is their distinct stages of life. At infancy, baby orangutans only weigh a few kilograms and are almost always carried by their mothers. Between 2.5 and 5 years of age, they will grow to 15 kilograms in juvenile-hood and will often play with peers and make small exploratory trips. As an adolescent, from 5 to 8 years, the orangutans will grow to 30 kilograms and develop stronger relationships outside their mothers. Females become fully developed after this and begin to have offspring of their own, while males enter a stage called sub-adulthood. Not until after about 15 years of age will the males join the female as full adults and reach their maximum weight.
When given the proper living conditions, Sumatran orangutans can live to 53-58 years of age. The major threat to this though is the use of palm oil as their habitat is cut down to make room for these plantations. Since 2000, the species has been assessed as critically endangered on the IUCN Red List as Sumatra has one of the highest deforestation rates in the world. Protecting the rainforest is essential to conserving Sumatran orangutans. Projects that help conserve and protect this environment can be found on the in the Indomalaya region.