Although orangutan society is admittedly less gregarious than other ape groups, that fact alone doesn't automatically make them introverts. In fact, orangutan mothers take care of their offspring until they're 7 or 8 years old -- one of the longest child/parent relationships of any animal in the world [source: Mayell, Orangutan Conservancy].
And while adult orangutans primarily hang out alone or in very small groups, they may be forced into that solitary lifestyle because of the converging factors of high caloric needs and limited resources. Orangutans are roughly 4.1 to 4.9 feet (1.25 to 1.5 meters) tall and weigh between 66 and 110 pounds (30 and 50 kilograms) for females and between 110 and 198 pounds (50 and 90 kilograms) for males [source: World Wildlife Fund].
Needless to say, maintaining such a physique on little more than vegetable matter requires a lot of work -- especially when food isn't widely abundant. This lack of food distribution limits the orangutan's ability to congregate. Say you're at a party in a high rise, and everyone is famished. There's going to be a lot less socializing if the cookies and punch are scattered throughout the building's 17 floors. Orangutans may simply live in a poorly planned jungle party.
Many scientists admit as much, saying that it's probably more accurate to label orangutans as "solitary but social," rather than semi-solitary. It may just seem like semantics, but there's a difference. Semi-solitary implies that their lifestyle is self-imposed, whereas calling them solitary but social indicates that they would be social if not for mitigating circumstances.
To further prove the point, researchers have observed orangutans using tools and signals -- evidence of learned behaviors that require close social interaction. Signals varied between different populations, indicating that the knowledge was culturally transmitted and not simply acquired individually or innately.
Dr. Carel van Schaik, a Dutch primatologist, discovered a group of orangutans in a highly productive swamp forest in northern Sumatra that were "every bit as sociable" as chimpanzees [source: Rogers]. It turns out that when orangutans live in a place where they don't need to compete for food, they socialize in large groups and even share with one another. The swamp had the highest density of orangutans ever recorded [source: Rogers].
So perhaps orangutans aren't quite the introverts initial reports made them out to be. Throw them a good enough party and they're all over it.
For more on orangutans and how you can help ensure they continue partying for many years to come, swing through some of the links on the next page.