PREVIEW

Like many humans young orangutans learn how to make their bed thanks to tuition from their mothers.

The great apes, one of our closest living genetic relatives, develop the complex skill of building night-time nests by closely observing others before practising the technique themselves, researchers have found.

Primatologists from the University of Warwick, working with the Max Planck Institute of Animal Behaviour in Germany, say the discovery reveals the importance of social learning in great apes.
Nest-building is often overlooked in studies of ape behaviour, but it is vital for arboreal species such as orangutans. A well-constructed nest helps them avoid predators, stay warm, sleep securely high in the canopy and even ward off mosquitoes.

Until now, however, it has been unclear how young orangutans learned to master such an intricate process.

Publishing in Nature Communications Biology, the researchers report that immature Sumatran orangutans acquire the skill by “peering” – deliberately watching the nest-building of their mothers and others – before practising the actions themselves.

Dr Ani Permana, lead author from Warwick’s Department of Psychology, 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 practising, 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 are usually simple structures, while night nests are elaborate platforms, sometimes as high as 20 metres up, with features such as linings for mattresses, pillows, blankets and even roofs for protection from rain.

The researchers found that when young orangutans peered at their mothers making nests, they were more likely to try building their own. If they were present but distracted, they did not practise – suggesting that active watching is crucial to learning.

Youngsters were especially attentive during the more complicated stages, such as weaving across multiple trees or adding comfort elements, and tended to practise more after observing these steps.

As they grew older, orangutans began observing individuals beyond their mothers, broadening their knowledge of tree species and construction techniques.

Dr Caroline Schuppli, senior author from the Max Planck Institute, 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 recognising 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 previously been documented in behaviours such as tool use, the team says this finding is significant because nests are essential for survival, nest-building is a complex multi-stage process, and it is an evolutionarily ancient behaviour dating back millions of years.

The researchers say the results suggest that the roots of cultural transmission in apes may be far older than previously thought.