Copying Others Can Help Young Orangutans Build A Broad Diet

Young orangutans who spend little time working out for themselves how to build a broad diet can partly compensate by watching how other orangutans choose what to eat.

The findings suggest that orangutans have different strategies for developing broad survival skills, says Revathe Thillaikumar at the Max Planck Institute of Animal Behavior in Germany.

Young orangutans acquire a substantial body of knowledge before they can survive independently, which they must do by the time they are 8.5 years old. This includes understanding what foods are safe to eat, where to find them and how to process them in a rainforest offering hundreds of food options of varying levels of accessibility – from easy-to-access leaves to the more inaccessible but also more nutritious seeds at the heart of a tough, spiny neesia fruit.

Scientists already know that orangutans can acquire this knowledge both by observing their mothers and other individuals in their social circle – a process known as social learning – and by exploring entirely on their own without any input from others, which is known as individual learning. But how these two forms of learning work together – and how they affect what orangutans learn to eat before becoming independent – hasn’t been clear.

To find out, Thillaikumar and her colleagues analysed nearly 7000 instances of learning recorded during more than 1700 hours of observations of wild Sumatran orangutans at Suaq Balimbing, a research station in Indonesia. The observations, collected over 12 years, tracked 21 youngsters as they closely watched other orangutans who were interacting with foods and other objects.

The young apes varied considerably in how much they relied on different kinds of learning, with some using more social learning, and others exploring independently much more often. This might, in part, reflect personality differences, and might also be influenced by early development – including differences in how mothers care for their young, says Thillaikumar.

Youngsters who learned by watching others also tended to continue manipulating new objects or trying new foods for about 145 minutes after they had closely observed another orangutan. This activity is reminiscent of the way in which children will spend time imitating an activity they have just seen demonstrated by an adult, says Thillaikumar. “Yeah, it’s practice.”

Next, the researchers drew on about 4700 hours of feeding observations for 13 of the youngsters to estimate the range of foods they had learned to eat by the time they reached independence. Unsurprisingly, the team found that the individuals who had engaged in plenty of social learning and plenty of individual learning had acquired the broadest diets.

But they also found that young orangutans who engaged in very little truly individual learning could partially compensate and develop a reasonably broad diet if they were good social learners.

Elizabeth Lonsdorf at Duke University in North Carolina says she’s impressed by the sheer scale of the work, following young orangutans through the rainforest across their entire, lengthy period of dependency on adults. She was particularly intrigued by how often social observation was followed by young orangutans practising the techniques they had observed. “In simpler terms, they show clearly what we see in human children and other apes – that they watch others perform a behaviour and then go try it out on their own.”

The variability in learning styles – even at an individual level – is especially interesting, says Michael Tomasello, also at Duke University. It suggests that no single form of learning can tell the whole story. “Predicting dietary breadth at maturity requires looking at all types of learning.”