Warwick primatologists, in collaboration with the Max Planck Institute, have shown that young orangutans develop their nighttime nest building skills via observational social learning – by closely watching others and then practicing these complex constructions.

Nest-building is an often-overlooked behaviour in great apes, but for arboreal species, a well-built nest is essential to survival. Nests are responsible for keeping apes safe from predators, helping them stay warm, providing a secure place to sleep when up high and have even been shown to have anti-mosquito properties. But how orangutans learn this complex ability has remained largely unclear.

Now, University of Warwick researchers have reported in Nature Communications Biology that immature Sumatran orangutans learn how to build these complex feats of engineering through carefully ‘peering’ at the workmanship of their mothers and others and practicing the steps they’ve paid careful attention to.

Dr. Ani Permana, Department of Psychology, University of Warwick, lead author of the paper said: “Nest-building is critical to survival in orangutans but is surprisingly not the focus of a lot of research. We previously reported that it takes multiple years for immature orangutans to learn to nest-build, but based on 17 years of observational data, this paper shows that this learning process is highly dependent on young animals carefully watching the nest-building of others.

“Orangutan nest-building tendency may have some innate basis, but the details and method must be socially learned starting from a very young age by watching and practicing, learning from mistakes as they grow and this paper is the first time this has been shown in wild apes.”

In the wild, Sumatran orangutans build two types of nests. Day nests tend to be basic practical frames, but the night nests are intricate sleeping platforms often built as high as 20 meters in the tree canopy and including comfort elements such as pillows, blankets, mattresses (linings) and roofs to protect from adverse weather.

By observing orangutans for long durations over many years, the research group managed to show that young orangutans peered at (deliberately watched) their mothers making nests to learn how to do it. When peering was observed, the immature orangutan was more likely to follow up by practicing nest-building themselves. If the immature orangutans were nearby when mum built a nest but didn’t watch for example because they were distracted, they generally didn’t go on to practice themselves – meaning active watching is likely crucial to developing the skill, strongly supporting the idea that this is observational social learning.

Immature orangutans were also shown to pay special attention to the more complicated parts of nest construction—like adding comfort elements or building across multiple trees—and practiced more after watching these actions.

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As the orangutans grew older, they began watching and learning from other individuals beyond their mothers, choosing new role models who can help diversify their knowledge of which trees to use, suggesting that both how to build, and what to build with, are learned socially.

Dr. Caroline Schuppli, Max Planck Institute of Animal Behavior, senior author of the study said: “Aside from learning ‘how to’ build a nest, immature orangutans also appear to learn the ‘know-what’ of which materials to use. The choice of tree species is important, and infants—who primarily peer at their mothers—are more likely to select the same species their mothers use.”

“Just like human teenagers finding their own path, maturing orangutans increasingly peer at the nest-building of others and begin experimenting with the tree species those individuals use.”

“Ultimately, adult orangutans tend to revert to the nest materials used by their mothers, perhaps recognizing that the most effective methods had already been established. This consistent variation in nest materials across generations indicates that wild orangutan populations possess cultural elements that could be lost without the conservation of the species and their habitats.”

While social learning has been documented for behaviours such as tool use (using a frayed stick for termite fishing), this discovery of observational social learning in nest-building is important with new implications because:

Nests are crucial for survival – suggesting a fundamental role for social learning in orangutan development.
Nest building is a complex multi-stage process – that social learning is powerful in orangutans, and they can learn complex processes through watching and practicing
Nest building is an evolutionarily old behaviour (existing in ape ancestors millions of years ago) – suggests an older origin for social learning in apes.

IMAGE CREDIT: Natasha Bartolotta @ SUAQ Project.