Orangutans in the Suaq forests of Sumatra make up for lost nighttime rest by taking strategic naps during the day, a new long‑term study finds. By observing 53 wild adults over 14 years—totaling 276 nights and 455 days—researchers discovered that these great apes extend their daytime nest‑based naps by roughly 5 to 10 minutes for every hour of sleep they miss overnight.
The team recorded orangutans spending nearly 13 hours each night in their woven canopy “beds,” yet factors like nearby companions, cooler nights, and longer daily travels trimmed their slumber. On days following shorter nighttime sleep, individuals racked up an average of 76 minutes of napping, divided across one to four simple day nests.
“Moving through the canopy, finding food, solving problems, navigating social relationships—these are all tiring and cognitively demanding tasks,” says Alison Ashbury, the study’s first author.
Wild orangutans build sturdy night nests—complete with leafy mattresses and pillows—in about ten minutes, but their day nests are quicker, simpler structures, often completed in under two minutes. Despite the reduced comfort, observers consistently saw orangutans reclining motionless with closed eyes, indicating genuine rest.
Associations with conspecifics also chipped away at both night and day sleep: each additional nearby orangutan shaved about 14 minutes off nightly rest and shortened cumulative nap duration. Colder nights and longer travel distances similarly reduced sleep periods, while higher daytime temperatures and rain prompted longer naps under the branches.
“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,” says Caroline Schuppli, the senior author.
Researchers note that Suaq orangutans are famed for sophisticated tool use and cultural innovations—behaviors that may heighten their need for restorative rest. By linking sleep deprivation to compensatory napping, this work illuminates how homeostatic sleep regulation evolved in our closest relatives and underscores the importance of studying sleep under natural ecological and social pressures.
The study has been published in Current Biology.
