There is a deep hole in a tree trunk and within is a tasty dollop of sweet, nutritious honey. It’s a worthwhile prize for any animal skilled or clever enough to reach it, and chimpanzees certainly have both of these qualities. But the solutions they find aren’t always the same – they depend on cultural traditions.
Chimps from the Sonso community in Uganda are skilled at the use of sticks and unsurprisingly, they manufacture stick-based tools to reach the honey. Chimps from the Kanyawara community in a different part of Uganda have never been seen to use sticks in the wild. Instead, they bring their considerable leaf-based technology to the fore, using leaves a sponges to soak up the hidden honey.
This is hardly the first time that chimps have demonstrated cultural traditions. Chimps in different parts of Africa have their own peculiar styles of tool technology and these variations are some of the strongest pieces of evidence for the existence of animal culture. Captive chimps can also transmit traditions between each other, once seeded by scientists.
But some sceptics are unconvinced. Their riposte is that genetic or environmental differences could equally have shaped technological differences. Alternatively, faced with abstract problems in captivity, chimps could learn solutions through trial-and-error, rather than picking up answers from their peers. To discount these possibilities, Thibaud Gruber from the University of St Andrews wanted to see if different groups of wild chimps would solve new problems in different ways, even though they shared similar genes and environments.
He found two groups of participants in the Sonso and Kanyawara communities of Uganda. Both live in forests and both are genetically similar enough that you couldn’t tell which group an individual chimp belonged to based on its genes. And both groups like honey.
When the chimps weren’t around, Gruber drilled holes in fallen logs, filled them with liquid honey, and dotted honeycombs around the rim to alert passing chimps. For such chimps, it would have been an unusual sight – they often rob beehives but the holes they pilfer are on vertical trunks, and the honey is solid, waxy and easily reachable.
If the hole was shallow, the chimps from both communities could use their hands to get the honey. For deeper prizes that could only be reached with tools, their strategies strongly differed – some of the Sonso chimps sponged the honey up with leaves, while almost all of the Kanyawara chimps dipped into it with sticks. No Sonso chimp used sticks and no Kanyawara chimp used leaves.
Gruber thinks that it’s extremely unlikely that the chimps were using a trial-and-error method to extract the honey, for they solved the problem both quickly and accurately. Despite having similar environments, genes and tasks, the two communities had their own specific approaches to the task. Their divergent cultures are reflected not just in the tools they used, but their
Kanyawara chimps try to eat honey about twice a month, and they succeed on around half of their attempts. In Sonso, honey is a much rarer part of the chimp diet. At both places, bees attack invading chimps with equal ferocity, but the Kanyawara group have become persistent and learned to regularly revisit the same spot. The Sonso group only eat honey when the opportunity presents itself. It’s no surprise then that the Kanyawara chimps spent longer in their quest for the hidden honey than their Sonso peers.
Reference: Current Biology DOI: 10.1016/j.cub.2009.08.060
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Aesop’s fable “The Crow and the Pitcher” has been confirmed in a wonderful experiment. In the classic tale, a thirsty crow uses stones to raise the level of water in a pitcher until it rises within reach of its beak. This is no mere fiction – rooks, close relatives of crows, have the brains to actually do this.
The aptly named Chris Bird, along with Nathan Emery, gave four captive rooks (Cook, Fry, Connelly and Monroe) a chance to reach a small worm floating in a cylinder of water, with nothing but a small pile of stones sitting on the side. All of them solved the task, and Cook and Fry succeeded on their first attempt. They were savvy about the stones too, using exactly the right number to bring the water within reach and preferring larger stones over smaller ones.
The accomplishments of Bird’s rooks are even more impressive when you consider that rooks are not natural tool-users. Many of the corvids – crows, ravens and the like – are avid tool-users and the skills of the New Caledonian crow are rapidly becoming the stuff of popular science legend. But rooks are different – even though they too excel in laboratory tests (as Bird and Emery have previously shown), they hardly ever use tools in the wild. Rather than any special tool-using adaptations, their skills must stem from the sort of general intelligence that great apes are thought to possess.
More so than other members of the family, rooks are extremely opportunistic feeders, relying on a varied menu of seeds, insects, dead meat and rubbish. With such catholic tastes, food is never far from their beaks and they may have little need for specialised tricks involving tools. The same might be true for capuchin monkeys, which happily brandish tools in a lab but only ever use them in the wild when food is scarce. As Aesop’s fable moralised, “Necessity is the mother of invention.”
Chimps are known to make a variety of tools to aid their quest for food, including fishing sticks to probe for termites, hammers to crack nuts and even spears to impale bushbabies. But a taste for honey has driven one group of chimps in Gabon’s Loango National Park to take tool-making to a new level.
To fulfil their sweet tooth, the chimps need to infiltrate and steal from bee nests, either in trees or underground. To do that, they use a toolkit of up to five different implements: thin perforators to probe for the nests; blunt, heavy pounders to break inside; lever-like enlargers to widen the holes and access the different chambers; collectors with frayed ends to dip into the honey; and swabbers (elongated strips of bark) to scoop it out.
Some of the tools are even fit for the Swiss army, combining multiple functions into the same stick. For example, some were obviously modified at both ends, but one was blunt while the other was frayed, suggesting that they doubled as enlargers and collectors.
These observations were made by Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology and they emphasise yet again the extraordinary brainpower of chimpanzees. It takes an uncommon intellect to be able to design and manufacture a suite of tools and use them in sequence to extract a foodstuff that’s hidden from sight.