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Tool use in chimpanzees

The use of tools by a non-human animal was first recorded in our closest living relative, the chimpanzee . Just like humans, chimpanzees create and use tools to make their lives easier.

Termites are one of chimpanzees' favourite foods – but how to reach the creatures deep within their mounds presents quite a problem. One day in Tanzania's Gombe National Park in 1960, Jane Goodall discovered how chimpanzees solve the difficulty. A chimp named David Greybeard picked up a twig and stripped the leaves off of it. Then he stuck the twig into one of the holes in the termite mound, left it there for a moment, and slowly pulled it out. As termites clung to the twig, David picked them off with his lips and scrunched them. He was using the stem as a tool to ‘fish’ for insects. This was modification of an object for a specific purpose, the making of a crude - but effective - tool. Soon after this discovery, Jane observed other chimps performing the same behaviour.

Some years later, using video recordings, researchers confirmed that chimps not only use a variety of tools but also design and make them  . The ‘tool kits’ of chimps in the Republic of Congo are among the most complex ever observed in wild chimp populations.

The chimps use one short stick to penetrate the aboveground mounds and then a "fishing probe" to extract the termites. For subterranean nests the chimps use their feet to force a larger "puncturing stick" into the earth, drilling holes into termite chambers, and then a separate fishing probe to harvest the insects.

According to Josep Call from the Max Planck Institute for Evolutionary Biology in Germany, to make a fishing probe the chimps first uproot the stem of a plant "or use their teeth to clip the stem at the base and then remove the large leaf from the distal end by clipping it with their teeth before transporting the stem to the termite nest." At the termite nest, "they complete tool manufacture by modifying the end into a 'paint brush' tip by pulling the stem through their teeth, splitting the probe lengthwise by pulling off strands of fiber, or separating the fibers by biting them."

The scientists determined the brush-tipped tool does a better job that plain-tipped sticks, since it retrieves more termites. Call explained that "termites can bite better the frayed ends since their mandibles get a better grip."

Call and his team are not certain how this particular group of chimpanzees devised the more advanced termite fishing probe. He said: "It could have been chance — a chimpanzee used it by chance and then it caught on. So far this is the only place where the brush manufacture has been described as a design feature, and not a by-product."

"It's exciting to watch these chimps do something that we've seen only people do before—use their feet to push the stick into the ground as a farmer might do with a shovel." said Pat Wright, a primatologist with the New York State's Stony Brook University.

The chimps use one particular tree species - Thomandersia hensiiv - to make their puncturing sticks and a herb - Sarcophrynium spp. - for their fishing probes. The preference for these trees suggests that chimps not only know which raw materials are best suited for each task but also travel to find them. The chimps arrive at the termite nests with the appropriate tools in hand, according to co-author Dave Morgan, a conservationist with Cambridge University in the U.K. and the Bronx-based Wildlife Conservation Society in New York.

Termite fishing is much tougher than one might think, said co-author Crickette Sanz, an anthropologist at Washington University in St. Louis, Missouri. Sanz and Morgan both tried fishing for the insects. After cracking through the sunbaked mounds or subterranean chambers with twigs or sticks, fashioning a good fishing probe is a challenge. The chimps even use special techniques for pulling the aggressive soldier termites off the end of the probe. "We were less successful than most of the youngsters—this is a complex skill that is developed with years of practice." Sanz said.

The video showed infants watching closely as mother chimps skillfully extract sticks swarming with large, shiny black termites. Through these social interactions, tool-using behaviours and techniques are passed from one individual to the next - what many scientists believe to be the hallmark of culture.

Other scientists have discovered that chimpanzees use and make other tools as well. Some chimps take a stick to scrape out food, just like a person might use a spoon to scoop out a tasty treat. Other chimps have learned to use leaves to help them drink. Chimpanzees sometimes can't reach water that has formed in hollows high up inside trees. So they take a handful of leaves, chew them, dip this “sponge” into the little pool and suck out the water.

Chimpanzees have also been seen using tools such as stone hammers  to chop up and reduce food into smaller bite-sized portions. Kathelijne Koops and Professor William McGrew of the Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, UK, studied a group of chimps living wild in the Nimba Mountains of Guinea, Africa. They found that the chimps use both stone and wooden cleavers, as well as stone anvils, to chop up the large hard Treculia fruits into smaller more manageable portions.

Koops found stone and wooden cleavers, as well as stone anvils used to fracture the large fruits. All were covered by the remains of smashed fruit and seeds. The cleavers were clearly used to pound the fruit, rather than the fruit pounded upon the stones. And the anvils were made from immoveable rocky outcrops.

Surprisingly, neighbouring chimps living in the nearby region of Seringbara do not process their food in this way, reinforcing how tool use among apes is culturally learnt.

Ms Koops said: "Chimpanzees across Africa vary greatly in the types of tools they use to obtain food. Some groups use stones as hammers and anvils to crack open nuts, whereas others use twigs to fish for termites." The apes' use of such tools can be surprisingly sophisticated. "For example, nut-cracking in the Bossou chimpanzee community in Guinea involves the use of a movable hammer and anvil, and sometimes the additional use of stabilising wedges to make the anvil more level and so more efficient." explains Ms Koops.
 
Chimpanzees in Fongoli, Senegal, have been observed making and using wooden spears to hunt other primates . They fashioned tools to jab at smaller primates sheltering in cavities of hollow branches or tree trunks. In one case the researchers witnessed a chimpanzee extract a bushbaby with a spear.

Chimps had not been previously observed hunting other animals with tools. Researcher Jill Pruetz, assistant professor of anthropology at Iowa State University, US, said: "There were hints that this behaviour might occur, but it was one time at a different site.... I saw about 13 different hunting bouts. So it really is habitual."

In most cases, the chimpanzees carried out four or more steps to manufacture spears for hunting. In all but one of the cases, chimps broke off a living branch to make their tool. They would then trim the side branches and leaves. In a number of cases, chimps also trimmed the ends of the branch and stripped it of bark. Some chimps also sharpened the tip of the tool with their teeth.

Many areas where chimpanzees live are also home to the red colobus monkey, which the chimps hunt. However, the Senegal site is lacking in this species, so chimps may have needed to adopt a new hunting strategy to catch a different prey - bushbaby.

Adult males have long been regarded as the hunters in chimp groups. However, females, particularly adolescent females, and young chimps in general were seen exhibiting this behaviour more frequently than adult males. "It's classic in primates that when there is a new innovation, particularly in terms of tool use, the younger generations pick it up very quickly. The last ones to pick up are adults, mainly the males." said Dr Pruetz. This is because young chimps pick the skill up from their mothers, with whom they spend a lot of their time. The researchers concluded that their findings support a theory that females may have played a similarly important role in the evolution of tool technology among early humans.

It has now been discovered that chimpanzees use objects - stems, twigs, branches, leaves, and rocks - in many different ways to accomplish tasks associated with feeding, drinking, cleaning and grooming themselves , investigating out-of-reach objects, and as weapons. In differing communities chimpanzees make and use different objects for different purposes.
These behaviours, passed from one generation to the next through observational learning, can be regarded as primitive cultures .

References

  • Sanz C, Call J and Morgan D 2009 Design complexity in termite-fishing tools of chimpanzees (Pan troglodytes) Biology Letters vol. 5 no. 3 293-296
  • Sans C, Morgan D and Gulick S 2004 New Insights into Chimpanzees, Tools, and Termites from the Congo Basin. The American Naturalist, Vol 164, No 5.
  • Mercader J, Barton H, Gillespie J, Harris J, Kuhn S, Tyler R and Boesch C 2007 4,300-Year-old chimpanzee sites and the origins of percussive stone technology. Proceedings of the National Academy of Science vol. 104 no. 9, 3043-3048.
  • Pruetz J. D and Bertolani P 2007 Savanna Chimpanzees, Pan troglodytes verus, Hunt with Tools. Current Biology, Volume 17, Issue 5, 412-417.
  • McGrew W. C and Tutin C. E. G 1973 Chimpanzee Tool Use in Dental Grooming. Nature 241, 477 – 478.
  • Whiten A, Horner V and de Waal F. B. M 2005 Conformity to cultural norms of tool use in chimpanzees. Nature 437, 737-740.

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