Sumatran orangutan - Ecology & Habitat

Stronger bonds than the Bornean species

Social Structure
Sumatran orangutans are reported to have closer bonds than in Borneo. This has been attributed to mass fruiting of the fig trees, where large groups come together to feed. Adult males are usually solitary while females are accompanied by offspring. Group size averages only 1.47 and both sexes have been observed to live in home ranges of 2-10 km², with considerable overlap. Both male and female adults form temporary associations with immature individuals.

Life Cycle
After weaning at about 3.5 years of age, young individuals become gradually independent of their mother after she gives birth to a second young. For the Sumatran orangutan, the youngest females to reproduce are 10-11 years of age, but the average age of reproduction is around 15 years of age.

Breeding
The interbirth interval for Sumatran orangutans is estimated to be as short as 6 years and as long as 10. The long period taken to reach sexual maturity, the long interbirth periods and the fact that orangutans normally give birth to just a single young mean that orangutans have an extremely slow reproductive rate. This makes orangutan populations highly vulnerable to excessive mortality, and means that populations take a long time to recover from population declines.

Diet
The diet of Sumatran orangutans includes more pulpy fruit and figs compared to that of Bornean orangutans.

About 60% of the orangutan's diet includes fruit (e.g. durians, jackfruit, lychees, mangosteens, mangoes and figs), while the rest comprises young leaves and shoots, insects, soil, tree bark, woody lianas, and occasionally eggs and small vertebrates. They obtain water not only from fruit, but also from tree holes.