When do you make your bed? In the morning when you wake up? If you were a chimpanzee—our closest genetic relative, with whom we share about 99% of our DNA—you'd probably do it at dusk, just before falling asleep. Primatologists call this "nest building."
In the trees, chimpanzees twist, break, and interlace branches into a circle, then line the nest with twigs and leaves. At sunset, they climb over the edge, settle in comfortably, close their eyes, and sleep until dawn. They also frequently build nests during the day—places where they can rest, play, groom, and eat.
This is an integral part of chimpanzee life. Like other great ape species, they've been doing this for millions of years, ensuring they have a safe place to spend their time. The better they rest and sleep, the more energy they have, and the better their brains memorize and process upcoming tasks.
But here's the interesting fact: as with many humans, there appears to be a sex difference among chimpanzees when it comes to nest building—females do it more often than males, and from an earlier age. This shows they are more independent earlier in life.
There appears to be a sex difference among chimpanzees when it comes to nest building: females do it more often than males, and from an earlier age. This shows they are more independent earlier in life.
Credit: Iulia Bădescu This is one of the conclusions of a new study co-led by Canadian primatologist Iulia Bădescu, an associate professor of anthropology at the University of Montreal, who has spent much of her career studying chimpanzees in Uganda's Kibale National Park, one of the species' primary habitats worldwide.
The study, whose findings are published in the
American Journal of Primatology, was written by a team of anthropologists from UdeM, the University of Toronto, and Yale University. The first author, Tara Khayer, was then an undergraduate biology student at UdeM and is now pursuing a master's in biochemistry there.
Study of 72 chimpanzees
Nest building requires learning from early childhood and a physical development threshold to handle tree branches.
Credit: Iulia Bădescu The researchers examined daytime nest building by 72 wild young chimpanzees in 2013–2014 and again in 2018 in a sector of the national park called Ngogo.
Iulia Bădescu's team assessed the effects of age, sex, and maternal parity (the number of times a mother chimpanzee has raised offspring) on the likelihood of a young chimpanzee building a nest. They also studied nest-building rates (frequency per hour) and durations among the young chimpanzees.
Compared to younger chimpanzees, older juveniles were more likely to build nests and did so more frequently, confirming primatologists' observations: nest building requires learning from early childhood and a physical development threshold to handle tree branches.
Significantly, the team found that young females were more productive in nest building than males, aligning with other developmental markers suggesting that females in certain chimpanzee communities achieve independence from their mothers at a younger age than males.
Variations by age and sex
Nests serve a functional sleep role for older chimpanzees but may be used more for play and environmental exploration when they are young.
Credit: Iulia Bădescu "The likelihood and overall rates of daytime nest building in wild baby chimpanzees varied by age and sex," explains Tara Khayer. "Older babies and females were more likely to build nests and did so more often than younger babies and males."
Among the young chimpanzees observed building nests at least once, the rates and durations were similar regardless of age, sex, or maternal parity, indicating little interindividual variation in nest-building skill development once they started.
The new study confirms earlier research showing that chimpanzees over four years old build more nests for resting than younger ones, meaning nests serve a functional sleep role for older chimpanzees but may be used more for play and environmental exploration when they are young.
"Nest building also represents a form of tool use, as chimpanzees must manipulate branches and other materials around them to construct their nest," notes Tara Khayer. "Like cracking nuts with stones or catching ants with sticks, nest building involves skillful use of their environment."
What does this mean for us?
"Humans also sleep in beds," says Iulia Bădescu, "so there are interesting evolutionary implications. Studying how chimpanzees learn to build nests from a young age helps us better understand how all hominids, including us, develop and acquire new skills."