There are two groups of orangutan in Bukit Lawang, they are semi-wild and the wild. Orangutan is known as the world's largest arboreal mammal, the adult males weigh between 50 to 90 kg, 1.25 to 1.6 m in height, while the adult females weigh between 30 to 50 kg and stand about 1 to 1.1 m in height. Sumatran orangutan is smaller than the Bornean orangutan. Orangutans are extremely rare to jump, they can jump but they can't do it often, the scientists said this is because "energetic knife-edge", that's why they are just swinging from one tree to another trees. The secret of orangutan movement is to use the natural moment of the trees to keep their own energy costs down. In this circumstance their extra mass is actually a benefit, allowing them to make their tree sway back and forth until it's close enough to the next tree to move on.
This is all about the energy balance, the orangutans don't have a reflex movement and based on their diet, it won't provide much raw energy that may create the ability of parkour moves like humans, chimpanzee or monkeys. Orangutans are also well known to be the energy-efficient mammals. For Sumatran orangutans, climbing down was not an option. Orangutans live high in the tropical canopy of forests, where they forage fruit and sleep in nests. The wild Sumatran orangutans never come to the ground, there are tigers on the forest floor and carnivores that may cause harm to them, so they spend all of their time in the trees. If a gap becomes too large, they could find themselves isolated in one area of forest, like in Batu Kapal.