10 Facts About Orangutans

Among the most distinctive-looking primates on Earth, orangutans are characterized by their high degree of intelligence, their tree-dwelling lifestyles, and their strikingly colored orange hair. Here are 10 essential orangutan facts, ranging from how these primates are classified to how often they reproduce.

There Are Two Identified Orangutan Species

An orangutan hangs onto a rope at the Semenggoh Wildlife Rehabilitation Center in Kuching, Borneo. Grant Dixon / Getty Images

The Bornean orangutan (Pongo pygmaeus) lives on the southeast Asian island of Borneo, while the Sumatran orangutan (P. abelii) lives on the nearby island of Sumatra, part of the Indonesian archipelago. P. abelii is much rarer than its Bornean cousin. There are estimated to be less than 10,000 Sumatran orangutans. By contrast, the Bornean orangutan is populous enough, at over 50,000 individuals, to be divided into three subspecies: the northeast Bornean orangutan (P. p. morio), the northwest Bornean orangutan (P. p. pygmaeus), and the central Bornean orangutan (P. p. wurmbi). No matter the species, all orangutans live in dense rain forests well stocked with fruit-bearing trees.

Orangutans Have a Very Distinctive Appearance

Orangutans are some of the Earth's most distinctive-looking animals. These primates are equipped with long, gangly arms; short, bowed legs; large heads; thick necks; and, last but not least, long, red hair streaming (in greater or lesser amounts) from their black hides. The hands of orangutans are very similar to those of humans, with four long, tapering fingers and opposable thumbs, and their long, slender feet also have opposable big toes. The odd appearance of orangutans can easily be explained by their arboreal (tree-dwelling) lifestyle. These primates are built for maximum flexibility and maneuverability.

Male Orangutans Are Much Bigger Than Females

As a rule, larger primate species tend to show more sexual differentiation than smaller ones. Orangutans are no exception: Full-grown males measure about five-and-a-half feet tall and weigh over 150 pounds, while full-grown females rarely exceed four feet tall and 80 pounds. There is significant differentiation between males, as well: Dominant males have enormous flanges, or cheek flaps, on their faces, and equally large throat pouches that they use to produce piercing calls. Oddly enough, although most male orangutans reach sexual maturity by the age of 15, these status-signaling flaps and pouches often don't develop until a few years later.

10 Facts About Primates

By Bob Strauss

Orangutans Are Mostly Solitary Animals

Unlike their gorilla cousins in Africa, orangutans don't form extensive family or social units. The largest populations are composed of mature females and their young. The territories of these orangutan "nuclear families" tend to overlap, so a loose association exists among handfuls of females. Females without offspring live and travel alone, as do adult males, the most dominant of which will drive weaker males from their own hard-won territories. Alpha males vocalize loudly to attract females in heat, while nondominant males engage in the primate equivalent of rape, forcing themselves on unwilling females (who would much rather mate with flanged males).

Female Orangutans Only Give Birth Every Six to Eight Years

Part of the reason there are so few orangutans in the wild is because females are far from profligate when it comes to mating and reproducing. Female orangutans reach sexual maturity by the age of 10, and after mating, and a gestation period of nine months (the same as humans), they give birth to a single child. After that, mother and child form an inseparable bond for the next six to eight years, until the adolescent male goes off on his own, and the female is free to mate again. Since the average life span of an orangutan is about 30 years in the wild, you can see how this reproductive behavior keeps populations from spiraling out of control.

Orangutans Subsist Mostly On Fruit

There's nothing your average orangutan enjoys more than a big, fat, juicy fig—not the kind of fig you buy at your corner grocery, but the giant fruits of Bornean or Sumatran ficus trees. Depending on the season, fresh fruit comprises anywhere from two-thirds to 90% of an orangutan's diet, and the remainder is dedicated to honey, leaves, tree bark, and even the occasional insect or bird's egg. According to one study by Bornean researchers, full-grown orangutans consume over 10,000 calories per day during peak fruit season—and this is when females also prefer to give birth, given the abundance of food for their newborns.

Orangutans Are Accomplished Tool Users

It's always a tricky matter to determine whether a given animal uses tools intelligently or is merely mimicking human behavior or expressing some hard-wired instinct. By any standard, though, orangutans are genuine tool users: These primates have been observed using sticks to extract insects from tree bark and seeds from fruit, and one population in Borneo uses rolled-up leaves as primitive megaphones, magnifying the volume of their piercing calls. What's more, tool use among orangutans seems to be culturally driven; more social populations evince more tool use (and quicker adoption of the use of novel tools) than more solitary ones.

Orangutans May (or May Not) Be Capable of Language

If tool use among animals is a controversial issue, then the issue of language is right off the charts. During the mid to late 1970s, Gary Shapiro, a researcher at the Fresno City Zoo in California, tried to teach primitive sign language to a juvenile female named Aazk and then to a population of once-captive orangutans in Borneo. Shapiro later claimed to have taught a juvenile female named Princess to manipulate 40 different symbols and an adult female named Rinnie to manipulate 30 different symbols. As with all such claims, though, it's unclear how much this "learning" involved genuine intelligence and how much of it was simple imitation and a desire to obtain treats.

Orangutans Are Distantly Related to Gigantopithecus

The appropriately named Gigantopithecus was a giant ape of late Cenozoic Asia, full-grown males measuring up to 10 feet tall and weighing as much as half a ton. Like modern orangutans, Gigantopithecus belonged to the primate subfamily Ponginae, of which P. pygmaeus and P. abelii are the only surviving members. What this means is that Gigantopithecus, contrary to popular misunderstanding, was not a direct ancestor of modern humans but occupied a distant side branch of the primate evolutionary tree. (Speaking of misconceptions, some misguided people believe populations of Gigantopithecus are still extant in the American northwest and account for sightings of "Bigfoot.")

The Name Orangutan Means 'Forest Person'

The very name orangutan is strange enough to deserve some explanation. The Indonesian and Malay languages share two words—"orang" (person) and "hutan" (forest), which would seem to make the provenance of orangutan, "forest person," an open-and-shut case. However, the Malay language also employs two specific words for orangutan, either "maias" or "mawas," leading to some confusion about whether "orang-hutan" originally referred not to orangutans but to any forest-dwelling primates. Further complicating matters, it's even possible that "orang-hutan" originally referred not to orangutans but to humans with severe mental deficiencies.