The orangutans are the two exclusively Asian species of extant great apes. Native to Indonesia and Malaysia, orangutans are currently found in only the rainforests ofBorneo and Sumatra. Classified in the genus Pongo, orangutans were considered to be one species. However, since 1996, they have been divided into two species: the Bornean orangutan (P. pygmaeus) and the Sumatran orangutan (P. abelii). In addition, the Bornean species is divided into three subspecies. Based on genome sequencing, the two extant orangutan species evidently diverged around 400,000 years ago. The orangutans are also the only surviving species of the subfamily Ponginae, which also included several other species, such as the three extinct species of the genus Gigantopithecus, including the largest known primate Gigantopithecus blacki. The ancestors of the Ponginae subfamily split from the main ape line in Africa 16 to 19 million years ago and spread into Asia.
Orangutans are the most arboreal of the great apes and spend most of their time in trees. Their hair is typically reddish-brown, instead of the brown or black hair typical of chimpanzees and gorillas. Males and females differ in size and appearance. Dominant adult males have distinctive cheek pads and produce long calls that attract females and intimidate rivals. Younger males do not have these characteristics and resemble adult females. Orangutans are the most solitary of the great apes, with social bonds occurring primarily between mothers and their dependent offspring, who stay together for the first two years. Fruit is the most important component of an orangutan’s diet; however, the apes will also eat vegetation, bark, honey, insects and even bird eggs. They can live over 30 years in both the wild and captivity.
Orangutans are more solitary than other apes. Males are loners. As they move through the forest they make plenty of rumbling, howling calls to ensure that they stay out of each other’s way. The “long call” can be heard 1.2 miles (2 kilometers) away.
Mothers and their young, however, share a strong bond. Infants will stay with their mothers for some six or seven years until they develop the skills to survive on their own. Female orangutans give birth only once every eight years—the longest time period of any animal. The animals are long-lived and have survived as long as 60 years in captivity.
Because orangutans live in only a few places, and because they are so dependent upon trees, they are particularly susceptible to logging in these areas. Unfortunately, deforestation and other human activities, such as hunting, have placed the orangutan in danger of extinction.
Orangutans are among the most intelligent primates. Experiments suggest they can figure out some invisible displacement problems with a representational strategy. In addition, Zoo Atlanta has a touch-screen computer where their two Sumatran orangutans play games. Scientists hope the data they collect will help researchers learn about socialising patterns, such as whether the apes learn behaviours through trial and error or by mimicry, and point to new conservation strategies. A 2008 study of two orangutans at the Leipzig Zoo showed orangutans can use “calculated reciprocity”, which involves weighing the costs and benefits of gift exchanges and keeping track of these over time. Orangutans are the first nonhuman species documented to do so. Orangutans are very technically adept nest builders, making a new nest each evening in only in 5 to 6 minutes and choosing branches which they know can support their body weight.