Orangutans show engineering skills when building nests
Orangutans show remarkably advanced engineering skills when making nests, researchers say.
The researchers, led by scientists at the University of Manchester, followed and filmed the apes in the forests of Sumatra.
The team also took orangutans' nests apart to see how they were constructed.
Their study, in the journal PNAS, reveals that the apes select thick branches for a scaffold and thinner branches for a springy mattress.
- All great apes make nests - gorillas, chimpanzees and bonobos, as well as orangutans. Unlike birds, apes make a new nest each night. They also often construct day nests - perhaps for a nap following a big feed. These are slightly more "haphazard" in their construction
- Young orangutans often build "practice nests", apparently honing their technique. But they will share a bed with their mother for up to eight years before they move into their own nest
Roland Ennos from the University of Manchester, a senior member of the research team, told BBC Nature that the behaviour revealed the animals' "sophisticated tool use and construction skills".
"They show a lot of engineering know-how in how they build their nests," he said.
As anyone who has ever tried to snap a live twig from a tree will know, living, green branches do not snap cleanly in half. Dr Ennos explained that the animals "made use" of this, bending and weaving large, flexible branches into a strong nest scaffold.
The animals then filled this scaffold with fine, leafy branches - making a comfortable bed.
PhD student Adam van Casteren, who led the research, spent a year in northern Sumatra following and studying orangutans.
Out of the trees
Human ancestors may not have been the first to move out of the trees. Researchers studying chimps in the Nimba Mountains of Guinea found that the animals slept both on the ground and in the trees. This behaviour suggests early hominins - ancestors that we share with chimpanzees - may have nested on the ground, too.
Although Homo erectus or "upright man" was the first species fully adapted to living on the ground, the authors of this study, published in the American Journal of Physical Anthropology think that moving from the trees to the ground was a more "deep-seated, gradual transition from tree-to-ground sleep".
He and his colleague, Julia Myatt from London's Royal Veterinary College, filmed the orangutans as they built their daily nests. The animals could complete this task in as little as five or six minutes.
Once the animals woke up and left their nests in the morning, Mr Van Casteren clambered in - some of them were at heights of over 30m - in order to measure them.
"I'd take each nest apart [and] take pieces of it back to our camp to test it," he told BBC Nature.
Mechanical tests revealed, he said, that orangutans were "choosing branches based on their structural properties".
"Male orangutans can weigh up to 80kg," Mr Van Casteren said, "and they nest very high up, so these need to be strong structures."
He added that studying our primate cousins revealed insight into the origin of our own "representational view of the world".
"Instead of just [seeing] a branch, the orangutans also see a nest-building material," he said.
Dr Amanda Seed, a researcher from the University of St Andrews, who specialises in animal behaviour, said it was "great to see such detailed study of nest construction in orangutans".
"Nest building in both apes and birds has received far less attention than tool use," she told BBC Nature, "perhaps because it has been assumed to have a larger genetic component, but recently studies of both groups have challenged that assumption."
The study, she added, revealed the potential "evolutionary significance" of nest-building.
Prof Richard Byrne, also from the University of St Andrews, agreed that nest-building had been "neglected" by researchers, because it was not considered to be advanced tool use.
"Researchers have defined a 'tool' as a detached object used to solve some problem as an extension of the body, and the nests made by apes are not detached - the branches are broken, but still attached to the tree," he explained to BBC Nature.
"But it may be the cognitive skills of nest building that really underpin the abilities that in humans - and to a much more limited extent, in chimpanzees - allow sophisticated tool manufacture."