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 among the most intelligent primates; they use a variety of sophisticated tools and construct elaborate sleeping nests each night from branches and foliage. The apes have been extensively studied for their learning abilities. There may even be distinctive cultures within populations. Field studies of the apes were pioneered by primatologist Birutė Galdikas. Both orangutan species are considered to be endangered, with the Sumatran orangutan being critically endangered. Human activities have caused severe declines in the populations and ranges of both species. Threats to wild orangutan populations include poaching, habitat destruction, and the illegal pet trade. Several conservation and rehabilitation organisations are dedicated to the survival of orangutans in the wild.
Orangutans have an enormous arm span. A male may stretch his arms some 7 feet (2 meters) from fingertip to fingertip—a reach considerably longer than his standing height of about 5 feet (1.5 meters). When orangutans do stand, their hands nearly touch the ground. Orangutans' arms are well suited to their lifestyle because they spend much of their time (some 90 percent) in the trees of their tropical rain forest home. They even sleep aloft in nests of leafy branches. They use large leaves as umbrellas and shelters to protect themselves from the common rains.
These cerebral primates forage for food during daylight hours. Most of their diet consists of fruit and leaves gathered from rain forest trees. They also eat bark, insects and, on rare occasions, meat. 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.