Baby orangutans spy on mom to build cozy treehouse nests

Great apes are impressive architects, but their tree top nest-building remains one of their most understudied abilities. For example, Sumatran orangutans (Pongo abelii), , are adept at constructing two kinds of abodes. The 200 pound primates may assemble barebone frames for shade and shelter during the day, but it’s a different story at night. Before turning in for the evening, orangutans will weave complex platforms as high as 65 feet in the tree canopy. These cozy dwellings are furnished with makeshift blankets, mattress linings, pillows, and even roofs to guard against inclement weather.

But what does it take for the critically endangered apes to learn how to build their shelters? To find out, primatologists at the Max Planck Institute and University of Warwick reviewed 17 years’ worth of observational data collected on 44 orangutans. According to their conclusions published in the journal Nature Communications Biology, the answer may have far more to do with apes’ innate curiosity and concentration skills than instinctual knowledge.

“Orangutan nest-building tendency may have some innate basis, but the details and method must be socially learned starting from a very young age,” University of Warwick psychologist and paper co-author Ani Permana said in a statement.

The team found that it doesn’t take long for an orangutan to begin showing interest in nest-building. By six months’ old, the infants are “peering” at their mothers’ techniques, as well as playing with nesting materials like twigs, branches, and leaves. Between the ages of one and four, the young apes start practicing how to build day nests while learning from their mistakes. Night nest lessons don’t start until around the age of three, and generally take around five years to master.

“Aside from learning ‘how to’ build a nest, immature orangutans also appear to learn the ‘know-what’ of which materials to use,” added animal behaviorist and study co-author Caroline Schuppli. “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.”

One of the team’s most striking realizations is that nest construction education doesn’t solely revolve around a mother’s abilities. Researchers confirmed that as orangutans matured, they expanded their pool of tutors to include other community members. These role models further reinforced knowledge on which trees to use, what materials to build with, and even which accessories to use when furnishing their nests. Schuppli compared the progression to our own peer-influenced adolescent development.

“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,” she said.

Despite the experimentation with other nesting techniques, the team noted that orangutans tend to eventually fall back on the same nesting materials used by their mothers, possibly because they recognize the value of tried-and-true building strategies. This consistency across generations points to shared cultural elements across wild orangutan populations. However, this vital knowledge will be lost without effective environmental conservation efforts.

Orangutan social learning has previously been documented for behaviors like tool usage, but the study marks the first confirmation of nest-building observational learning. The implications are vast, particularly for understanding the importance of social knowledge construction among great apes. It also suggests nest building is an ancient evolutionary behavior that dates back millions of years ago, suggesting that there are older psychological underpinnings behind why we primates need a comfy place to lay our heads.

 

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