In the wild, tool use has been observed in Gunung Leuser National Park in Sumatra. The Orang-utan is the most solitary of the Great Apes. The longest bond is between mother and offspring. Although juveniles may associate in small groups, adults are usually hostile towards each other, except during mating season. Males and females without offspring travel alone.
Adult males have large territories which they defend from other males.
But the home ranges of several males often overlap. To avoid violent disputes, males make their distinctive 'long call', unique to Orang-utans. These are roars are amplified by the male's huge throat pouch, which acts as a resonating chamber and produces a booming that can be heard up to 1km away. In this way, males can avoid each other. It also tells females where the males are when the females are ready to mate.