A little honey goes a long way toward tool use.
Hawa is a chimpanzee living in the Budongo Forest of Uganda. The long-distance journeys Hawa takes during the days sap his energy, so he has learnt to replenish himself by extracting honey from logs
Hawa has a friend named Squibs, who never roams far from home. As a result, Squibs has never needed to acquire skills to obtain the energy-dense treat.
It’s a pattern that researchers working in the forest have documented over 6 years of field experiments and have now published in the journal eLife.
Hawa and Squibs are members of a large chimpanzee community, in which tool use for feeding is limited to folding leaves to collect water and using moss to soak up mineral deposits from a clay pit.
Curious about the motivations behind their rare tool use, study lead author Thibaud Gruber, from the University of Geneva, deployed the “honey trap experiment.” Holes too small for the chimpanzees to stick their fingers into were drilled into logs and partially filled with honey — just to the point that the honey could only be accessed with some sort of implement.
Only 11 of the 52 chimpanzees that engaged with the honey-filled logs used tools — either a folded leaf or a stick — and these individuals were rewarded with the sticky indulgence.
Who were these industrious chimps?
It turned out they were the ones who tended to travel the farthest each day. "Our results show that travel fosters tool use in wild chimpanzees and it may also have been a driving force in early technological evolution by humans," said Gruber in a press release.
The researchers wanted to know if their observed patterns of travel and tool use held up in other closely related species, so they combed through the literature.
Bonobos travel around the same average distances as the chimpanzees, and use a similar set of tools. By contrast, gorillas and orang-utans hardly ever use tools for feeding and spend much less time travelling than chimpanzees. Modern human hunter-gatherers are on the other end of the spectrum, walking great distances each day and using a greater variety of tools than any of the great apes.
Over the last few decades, the food supply in the Budongo Forest has steadily decreased, requiring the chimpanzees to travel further to obtain ripe fruits. Longer travel has likely fuelled the development of tool use, which was previously lacking in the community.
Declining habitat caused by climate change may have similarly been linked with increasing tool use and sociality in early humans, researchers believe.
"When times are changing, you have to adapt your behavior and our data illustrate that chimps will pay more attention to the possibilities offered by their environment in more demanding periods," says Gruber.
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