A new study concludes that even very young Sumatran orangutans (Pongo abelii) start forming ideas about their world, and how and when to use certain tools. Ape cultural traditions might not be very different from the cultural traditions of humans.
The scientists published their findings in the journal Current Biology¹. Orangutans have behavioral traditions that vary by regions. Orangutans in one area might use tools and others in another don’t. On the island of Sumatra in western Indonesia, orangutans by age 6 or 7 use sticks to probe logs for honey in the swampy regions west of the Alas River. Researchers have never observed this behavior in orangutans in coastal areas east of the river.
Experts think that social learning is the key difference. The ape figures out how to honey-dip by watching others. But that isn’t always easy to prove and some researchers still believe that wild apes could be influenced by their environment more than by social learning.
Deforestation has caused large numbers of orangutan orphans, many of whom come from both sides of the river. They wind up at the Batu Mbelin shelter in northern Sumatra. The team gave the orangutans two stick-based challenges. They involved raking food into their cages and dipping for honey. Apes from both sides of the river picked up the raking behavior quickly. This indicates that all the animals could understand using sticks as tools. Nine of the 13 west-side apes knew how to honey-dip while only two of the 10 east-side apes did. The west-side apes were just 4 years old on average, which is too young to have begun honey-dipping on their own in the wild. The researchers believe that this learned behavior came from observing their elders performing this task.
The researchers call such mental representations of stick use cultural ideas. The behavioral differences among apes are closer to the ones between humans, which also often stem from ideas. The study isn’t conclusive about when orangutans start developing stick skills in the wild.
- Gruber, T., et al., Current Biology, Volume 22, Issue 23, 2231-2235, 08 November 2012, doi: 10.1016/j.cub.2012.09.041