Orangutan Biology

Orangutan is a Malaysian word meaning "people of the forest," a fitting name as orangutans actually share 97% of their DNA with humans. They possess great intelligence and other human-like characteristics, such as the ability to use tools.  Orangutans also demonstrate great capacity to reason, solve problems, and even use computers, as noted by the National Zoo in Washington, DC.
Unfortunately, orangutans are one of the least understood of all apes and face constant threats from humans due to illegal trade, and destruction of their habitat for palm oil and pulp paper.
Orangutans are the only apes that inhabit Asia.  The Bornean orangutan – and three subspecies, the Northwest, Central and Northeast Bornean orangutan – inhabits the island of Borneo, and the Sumatran orangutan inhabits the island of Sumatra. They are considered arboreal mammals, meaning they predominantly live within the rainforest canopy, and are the largest arboreal mammal found on earth today.
Orangutans move around in the canopy by performing brachiation, the arboreal locomotion of swinging from branch to branch.  Because they are capable of quadrumanous scrambling, or the ability to use their feet just as they would their hands, brachiation comes easily to them.  Their opposable thumbs and big toes allow them to hook on to tree branches; and their highly mobile hip and shoulder joints allow them to easily move from branch to branch.  Interestingly, orangutans don’t even have a ligamentum teres, the ligament that binds the top of the femur to the pelvis.  This allows them to do yoga-like poses, such as putting their legs behind their head; a skill that would require years of training for humans.
Orangutans are the only primate species that has two different types of mature males, flanged and unflanged. Flanged males have their secondary sexual characteristics and are often twice the size of females. They possess a long, dark coat on their back and pronounced cheek pads. Their throat sac is used for "long calls" (heard up to 3 kilometers away) and often used during mating, or to warn off other flanged males.  
Unflanged males, who do not yet possess secondary sexual characteristics, are often the same size as adult females.  Since their flanges and throat sacs are not yet formed, they cannot emit long calls. They are able to produce offspring and contribute to the reproduction of their species however, flanged males still dominate reproduction of the orangutan population.
The transition from unflanged to flanged depends on complex social cues that are not yet fully understood.
Females, who mature between the ages of 10 and 15, give birth to one infant every six to eight years, totaling four to six offspring in a lifetime.  This long span between pregnancies is one of the reasons why the orangutan population is so difficult to regenerate.  A normal pregnancy lasts approximately eight months and infants typically weigh around 3.5 lbs.  Mothers nurse their offspring for six to eight years and typically carry them while moving from tree to tree until the infant reaches about five years of age.

While a male orangutan will leave his mother after puberty, a female orangutan will stay to learn important parenting skills, like watching her mother take care of her infants. In fact, female orangutans visit their mothers until about 15 to 16 years of age. Studies indicate that Bornean orangutans may become more independent at an earlier age than Sumatran orangutans.

About 60% of an orangutan’s diet consists of fruit.  However, they also eat bark, honey, flowers, insects, young leaves, vines, and the inner shoots of plants. Their preferred food is the fruit from durian trees, called the “king of fruits,” which they find in the wild or in cultivated gardens.  This large fruit tastes like a sweet, cheesy, garlic custard, and has a very pungent smell. Orangutans eat the flesh, discard the skin, and spit out the seeds, therefore playing a vital role in seed dispersal.
In some regions, orangutans occasionally eat soil, ingesting minerals that may neutralize the high quantities of toxic tannins and acids in their primarily vegetarian diet.  Conversely, orangutans in Sumatra occasionally eat lorises, small nocturnal primates, taking them out of the tree holes they sleep in.

Orangutan Odysseys

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