Anyone who has ever tossed and turned at night knows how much sleep matters. Stress, social distractions, and even the weather can disrupt our rest. And it turns out we’re not the only ones.
Orangutans – some of our closest living relatives – face similar challenges, and they’ve figured out a relatable solution: they nap.
Life in the rainforest is no easy task for orangutans. Every day involves travel, food gathering, social puzzles, and constant movement – mental and physical strain is inevitable.
“Moving through the canopy, finding food, solving problems, navigating social relationships; these are all tiring and cognitively demanding tasks,” said Alison Ashbury, the study’s first author.
“When an orangutan doesn’t get enough sleep, it does what any sleep-deprived human might do: it climbs into bed, lies down, and takes a nap.”
Scientists from the Max Planck Institute of Animal Behavior (MPI-AB) and the University of Konstanz in Germany, together with collaborators at the Universitas Nasional in Indonesia, studied wild orangutans in the rainforests of Sumatra.
The goal was to understand how these great apes manage their sleep in the wild and what that can teach us about the evolution of rest in primates.
For over 14 years, the team collected behavioral data on 53 adult orangutans at the Suaq Balimbing Monitoring Station. They followed the animals through 455 days and nights, closely watching how and where they slept.
Each evening, adult orangutans build a sleeping “nest” high in the treetops. This nest acts as a bed, with branches woven together to form a secure platform.
The orangutans even add leaves for a mattress and pillow. Mothers share nests with their nursing babies, but otherwise, adults sleep solo. At dawn, they leave the nest and begin the day.
“From our point of view on the ground, we usually can’t see orangutans at all in their night nests, but we can hear them rustling around, getting comfortable,” said Caroline Schuppli, the study’s senior author and a group leader at MPI-AB. “Eventually, everything goes quiet and still. And the reverse happens in the morning.”
The researchers measured the period of nighttime silence as a proxy for sleep. Although they couldn’t directly monitor brain activity, the length of this quiet period closely matched patterns of actual sleep observed in captive orangutans and wild baboons. On average, orangutans slept for nearly 13 hours each night.
Several factors disrupted sleep. Orangutans had shorter sleep periods when they built their nests close to others and when nights were colder. Sleep was also reduced on days when they had traveled farther.
“We thought it was really interesting that just being near other orangutans when building a night nest was linked to shorter sleep periods,” said Ashbury. “Imagine you stay up late hanging out with your friends, or your roommate is snoring so loudly in the morning that you get up early. I think it’s a bit like that.”
“They’re prioritizing being social over sleeping, or their sleep is being disrupted by others nearby, or even both.”
The team also explored how orangutans compensate for lost sleep. They found a consistent pattern: when orangutans had shorter nighttime sleep, they napped more during the day. In fact, for every hour less sleep the night before, they added 5 to 10 extra minutes of nap time the next day.
“For people, even a short nap can have significant restorative effects,” noted the researchers. “It’s possible that these naps are helping orangutans reset physiologically and cognitively after a poor night’s sleep, just like they do in humans.”
The orangutans used simple, quickly built day nests for these naps. These nests took less than two minutes to construct, lacked many of the comfort features of night nests, and were used solely for short rest periods.
“Day nests are less sophisticated, have fewer comfort elements, and are made quicker than night nests,” said Schuppli. “But even so, when we’re able to see an orangutan resting in a day nest, we see that their bodies are relaxed and their eyes are closed. They really do appear to be sleeping.”
Scientists have long recognized the Suaq orangutans for their exceptional mental abilities. Their frequent napping habits may play a role in supporting this cognitive edge.
“Among all studied orangutan populations, the Suaq orangutans arguably exhibit the widest range of cognitively demanding behaviors,” said Schuppli, who also directs research at the site.
“This may be linked to their relatively high propensity for daytime nest use. Either they need these high-quality naps to meet their cognitive demands, or their cognitive abilities can come about because they take high-quality naps in day nests so often.”
Another possible factor is their semi-solitary lifestyle. Orangutans don’t live in tight social groups, so they’re free to nap when they feel the need.
The data showed that orangutans took at least one nap on 41% of observed days, and those naps averaged 76 minutes.
“Studying sleep in the wild, in the natural social and ecological conditions under which it evolved, is important to broadening our understanding of the evolutionary origins and the ultimate functions of sleep,” said Meg Crofoot, director at MPI-AB and a professor at the University of Konstanz.
“Why did animals, from humans to primates to spiders to jellyfish, evolve to spend such large portions of their lives in this vulnerable unconscious state? If we’re going to answer this question, we need to bring sleep research out of the lab and into the field. Studies such as this one contribute to that effort.”
Orangutans napping in leafy nests may seem like a simple sight. But their resting habits may hold deeper clues about sleep’s role in intelligence, social life, and survival – for them and for us.
The full study was published in the journal Current Biology.
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