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Aman, a mighty male Borneo orangutan Learn more about him at the bottom of this article Photo: William O'Neal
Critically endangered Sumatran orangutans
Young Bornean orangutan
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Wild Bornean Orangutan courtesy of ARKive.org
Wild Sumatran Orangutan courtesy of ARKive.org
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Orangutan: “Person of the Forest” Catching sight of an orangutan in its natural habitat is no easy task! These arboreal (tree-dwelling) apes spend 90% or more of their time high in the treetops of the Indonesian rainforest, and unlike most primates they usually travel quietly and alone. But the ‘red ape’ is definitely worth finding and studying, especially before they disappear from the wild. Orangutans are the only great ape other than humans to live outside of Africa, and there are two recognized species: one on the island of Borneo (Pongo pygmaeus) and one on the island of Sumatra (Pongo abelii). Though they have been geographically separated for over one million years, all orangutans share a general set of physical characteristics that includes red hair, close-set eyes, and very long arms, fingers, and toes that help them move through the treetops in a mode of locomotion known as “quadrumanous climbing”. Both species also exhibit a high degree of sexual dimorphism (difference in male and female body size). Males weigh an average of 87 kg (191 lb) compared to an average weight of 37 kg (81 lb) in females. In addition to their size, adult male orangutans are easily identified by their long red hair, flaring cheek pads (called flanges), and the large throat sac they use to produce vocalizations known as ‘long calls’, which can be heard over a mile away. Orangutans are primarily frugivores (fruit-eaters), preferring to eat items such as figs and the fruit of the durian tree. During times of low fruit availability, however, orangutans forage opportunistically and eat insects, flowers, and other plant parts including leaves, bark, and pith. Observations of meat-eating by orangutans are rare, although recent data suggest that members of some orangutan populations are able to catch and eat fish. In both species of orangutans, males defend territories which may contain several females and their dependent offspring. Because the average interbirth interval for a female orangutan is approximately 8 years, the longest of any mammal species, males frequently fight each other for access to reproductive females and can sustain serious wounds in the process. In general, females prefer to mate with large, dominant males, but consortships with subordinate and adolescent males do occur. Researchers have also discovered that “forced copulations” frequently occur between less desirable males and females who resist their mating efforts. Wild female orangutans usually give birth to their first offspring around the age of 15. Young orangutans are very dependent on their mothers, sometimes breastfeeding for as long as 6 years. Even after they are weaned, young animals may continue to travel and sleep with Mom for several more years before they become fully self-sufficient. During this time they learn survival skills such as how to locate food, which items to eat, and how to build a new sleeping nest each night. Like chimpanzees, orangutans in the wild have proven to be cognitively complex creatures, capable of making and using a variety of tools and demonstrating sophisticated problem-solving abilities. Carel Van Schaik and other leading orangutan researchers have also established that orangutan populations pass on local cultural traditions such as using sticks to access the seeds of the Neesia fruit, the interior of which is protected by needle-like hairs. In captivity, orangutans have demonstrated success in additional cognitive challenges including learning sign language and communicating via computer lexigram (symbol-based) systems. Sadly, both Bornean and Sumatran orangutans face significant challenges to their continued existence in Southeast Asia. The IUCN currently lists the Bornean orangutan as “endangered” and the Sumatran orangutan as “critically endangered”. Major threats to both species include habitat loss due to fires, the conversion of forests to palm oil plantations and other types of agricultural land, and legal and illegal logging enterprises, as well as hunting and the illegal pet trade. The development of new networks of roads also continues to fragment orangutan habitat and further magnify these pressures. At current rates of population decline, orangutans may face extinction in the wild within the next 10-20 years.
Contributed by Lara Durgavich, PhD candidate in Biological Anthropology and NEPS Humane Education Program team member ~ To learn more about Aman and other very special orangutans at the Matang Wildlife Center for orphaned and displaced orangutans in Malaysian Borneo, check out William O'Neal's Letters From the Field blogs:
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