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Article 11 Dim Forest, Bright Chimps In the rain forest of Ivory Coast, chimpanzees meet the challenge of life by hunting cooperatively and using crude tools Christophe Boesch and Hedwige Boesch-Achermann Tal National Park, Ivory Coast, De- on, we were most interested in the that group hunting and cooperation were cember 3, 1985. Drumming, barking, chimps' use of natural hammers- key ingredients in the evolution of and screaming, chimps rush through the branches and stones-to crack open the Homo sapiens. The argument has been undergrowth, little more than black five species of hard-shelled nuts that are modified considerably since Dart first shadows. Their goal is to join a group abundant here. A sea otter lying on its put it forward, and group hunting has of other chimps noisily clustering back, cracking an abalone shell with a also been observed in some social car- around Brutus, the dominant male of rock, is a familiar picture, but no pri- nivores (lions and African wild dogs, for this seventy-member chimpanzee com- mate had ever before been observed in instance), and even some birds of prey. munity. For a few moments, Brutus, the. wild using stones as hammers. East Nevertheless, many anthropologists still proud and self-confident, stands fairly Africa's savanna chimps, studied for de- hold that hunting cooperatively and still, holding a shocked, barely moving cades by Jane Goodall in Gombe, Tanza- sharing food played a central role in the red colobus monkey in his hand. Then nia, use twigs to extract ants and termites drama that enabled early hominids, he begins to move through the group, from their nests or honey from a bees' some 1.8 million years ago, to develop followed closely by his favorite females nest, but they have never been seen using the social systems that are so typically and most of the adult males. He seems hammerstones. human. to savor this moment of uncontested su- As our work progressed, we were We hoped that what we learned periority, the culmination of a hunt high surprised by the many ways in which about the behavior of forest chimpan- up in the canopy. But the victory is not the life of the Tal forest chimpanzees zees would shed new light on prevailing his alone. Cooperation is essential to differs from that of their savanna coun- theories of human evolution. Before we captUring one of these monkeys, and terparts, and as evidence accumulated, could even begin, however; we had to Brutus will break apart and share this differences. in how the two populations habituate a community of chimps to our. highly prized delicacy with most of the hunt proved the most intriguing. Jane presence. Five long years passed before main participants of the hunt and with Goodall had found that chimpanzees we were able to move with th'em on the females. Recipients of large portions hunt monkeys, antelope, and:wild pigs, their daily trips through the forest, of will, in turn, share more or less gener- findings confirmed by Japanese biolo- which "our" group appeared to claim ously with their offspring, relatives, and gist Toshida Nishida, who conducted a sometwelve square miles. Chimpanzees friends. long-term study 120miles south of Gom- are alert and shy animals, and the lim- In 1979, we began a long-term study be, in the Mahale Mountains.So we were ited field of view in the rain forest- of the previously unknown chimpanzees not surprised to discover that the Tal . about sixty-five feet at best-made of Tal National Park, 1,600 square miles chimps eat meat. What intrigued us was finding them more difficult. We had to of tropical rain forest in the Republic of the degree to which they hunt coopera- rely on sound, mostly their vocalizations the Ivory Coast (Cote d'Ivoire). Early tively. In 1953 Raymond Dart proposed and drumming on trees. Males often Reprinted with permission from Natural History, September1991, pp. 50, 52-56. «J 1991 by the American Museum of Natural History. 63 2 .:. PRIMATES drum regularly while moving through of four to forty-five pounds. Stones of of monkeys are more apt than others to the forest: pant-hooting, they draw near any size, however, are a rarity in the for- wind up as a meal for the chimps. The a big buttress tree; then, at full speed est and are seldom.conveniently placed relatively sluggish and 1arge (almost they fly over the buttress, hitting it re- near a nut-bearing tree. By observing thirty pounds) red colobus monkeys are peatedly with their hands and feet. closely, and in some cases imitating the the chimps' usual fare. (Antelope also Such drumming may resound more than way the chimps handle hammerstones, live in the forest, but in our ten years at half a mile in the forest. In the begin- we learned that they have an impressive Tal, we have never seen a chimp'catch, ning, our ignorance about how they ability to find just the right tool for the or even pursue, one. In contrast, Gombe moved and who was drumming led to job at hand. Tal chimps could remember chimps at times do come across fawns, failure more often than not, but eventu- the positions of many of the stones scat- and when they do, they seize the oppor- ally we learned that the dominant males tered, often out of sight, around a panda tunity-and the fawn.) drummed during the day to let other tree. Without having to run around re- The six males moved on silently, group members know the direction of checking the stones, they would select peering up into the vegetation and stop- travel. On some days, however: intermit- one of appropriate size that was closest ping from time to time to listen for the tent drumming about dawn was the only to the tree. These mental abilities in spa- sound of monkeys. None fed or signal for the whole day. If we were out tial representation compare with some groomed; all focused on the hunt. We of earshot at the time, we were often of those of nine-year-old humans. followed one old male, Falstaff, closely, reduced to guessing. To extract the four kernels from in- for he tolerates us completely and is one During these difficult early days, one side a panda nut, a chimp must use a of the keenest and most experienced feature of the chimps' routine proved to hammer with extreme precision. Time hunters. Even from the rear, Falstaff set be our salvation: nut cracking is a noisy and time again, we have been impressed the pace; whenever he stopped, the business. So noisy, in fact, that in the to see a chimpanzee raise a twenty- others paused to wait for him. After early days of French colonial rule, one pound stone above its head, strike a nut thirty minutes, we heard the unmistak- officer apparently even proposed the with ten or more powerful blows, and able noises of monkeys jumping from theory that some unknown tribe was then, using the same hammer, switch to branch to branch. Silently,. the chimps forging iron in the impenetrable and delicate little taps from a height of only turned in the direction of the sounds, dangerous jungle. four inches. To finish the job, the scanning the canopy. Just then, a diana Guided by the sounds made by the chimps often break off a small piece of monkey spotted them and gave an alarm chimps as they cracked open nuts, twig and use it to extract the last tiny call. Dianas are very alert and fast; they which they often did for hours at a time, fragments of kernel from the shell. In- are also about half the weight of colobus we were gradually able to get within triguingly, females crack panda nuts monkeys. The chimps quickly gave up sixty feet of the animals. We still seldom more often than males, a gender differ- and continued their search for easier, saw the chimps themselves (they fled if ence in tool use that seems to be more meatier prey. we came too close), but even so, the evi- pronounced in the forest chimps than in Shortly after, we heard the charac- dence left after a session of nut cracking their savanna counterparts. teristic cough of a red colobus monkey. taught us a great deal about what types After five years of fieldwork, we Suddenly Rousseau and Macho, two of nuts they were eating, what sorts of were finally able to follow the chimpan- twenty-year-olds, burst into action, run- hammer and anvil tools they were using, zees at close range, and gradually, we ning toward the cough. Falstaff seemed and-thanks to the very distinctive noise gained insights into their way of hunt- surprised by their precipitousness, but a nut makes when it finally splits ing. One morning, for example, we fol- after a moment's hesitation, he also ran. open-how many hits were needed to lowed a group of six male chimps on a Now the hunting barks of the chimps crack a nut and how many nuts could three-hour patrol that had taken them mixed with the sharp alarm calls of the be opened per minute. into foreign territory to the north. (Our monkeys. Hurrying behind Falstaff, we After some months, we began catch- study group is one of five chimpanzee saw him climb up a conveniently situ- ing glimpses of the chimpanzees before groups more or less evenly distributed in ated tree. His position, combined with they fled, and after a little more time, the Tal forest.) As always during these those of Schubert and Ulysse, two ma- we were able to draw close enough to approximately monthly incursions, ture chimps in their prime, effectively watch them at work. The chimps gather which seem to be for the purpose of ter- blocked off three of the monkeys' pos- nuts from the ground. Some nuts are ritorial defense, the chimps were totally sible escape routes. But in,another tree, tougher to crack than others. Nuts of the silent, clearly on edge and on the lookout nowhere near any escape route and thus Panda oleosa tree are the most demand- for trouble. Once the patrol was over, useless, waited the last of the hunters, ing, harder than any of the foods pro- however,and they were back within their Kendo, eighteen years old and the least cessed by present-day hunter-gatherers own borders, the chimps Shiftedtheir at- experienced of the group. The monkeys, and breaking open only when a force of tention to hunting. They were after mon- taking advantage of Falstaff's delay and 3,500 pounds is applied. The stone ham- keys, the most abundant mammals in the Kendo's error, escaped. mers U!?ed the Tal chimps range from by forest. Traveling in large, multi-species The six males moved on and within stones of ten ounces to granite blocks groups, some of the forest's ten species five minutes picked up the sounds of an- 64 ~ 11. Dim Forest, Bright Chimps other group of red colobus. This time, Alone or in pairs, chimps succeed less of dry, open environments have been the chimps approached cautiously, no- than 15 percent of the time, but when found at all early hominid excavation body hurrying. They screened the can- three or four act as a group, more than . sites in Tanzania, Kenya, South Africa, opy intently to locate the monkeys, half the hunts result in a kill. The and Ethiopia. That the large majority of which were still unaware of the ap- chimps.seem well aware of the odds; 92 apes in Africa today live west of the Rift - proaching danger. Macho and Schubert percent of all the hunts we observed Valley appears to many' anthropologists chose two adjacent trees, both full of were group affairs. to lend further support to the idea that monkeys, and started climbing very qui- Gombe chimps also hunt red colobus a change in environment caused the etly, taking care not to move any monkeys, but the percentage of group common ancestor of apes and humans branches. Meanwhile, the other four hunts is much lower: only 36 percent. to evolve along a different line from chimps blocked off anticipated escape In addition, we learned from Jane Goo- those remaining in the forest. routes. When Schubert was halfway up, dall that even when Gombe chimps' do Our observations, however, suggest the monkeys finally detected the two hunt in groups, their strategies are dif- quite another line of thought. Life in chimps. As we watched the: colobus ferent. When Tal chimps anive under-a dense, dim forest may require more so- monkeys take off in literal panic, the ap- group of monkeys, the hunters scatter, phisticated behavior than is commonly propriateness of the chimpanzees' sci- often silently, usually out of sight of one assumed: compared with their savanna entific name-Pan came to mind: with another but each aware of the others' po- relatives, Tal chimps show greater com- a certain stretch of the imagination, sitions. As the hunt progresses, they plexity in both hunting and tool use. Tal the fleeing monkeys could be shep- gradually close in, encircling the quarry. chimps use tools in nineteen different herds and shepherdesses frightened at Such movements require that each ways and have six different ways of the sudden appearance of Pan, the wild chimp coordinate his movements with making them, compared with sixteen Greek god of the woods, shepherds, those of the other hunters, as well .as uses and three methods of manufacture and their flocks. with those of the prey, at all times. at Gombe. Taking off in the expected direction, Coordinated hunts account for 63 Anthropologist colleagues of mine the monkeys were trailed by Macho and percent of all those observed at Tal but have told me that the discovery that Schubert. The chimps let go with loud only 7 percent of those at Gombe. Jane some chimpanzees are accomplished us- hunting barks. Trying to escape, two Goodall says. that in a Gombe group ers of hammerstones forces them to look colobus monkeys jumped into smaller hunt, the chimpanzees typically travel with a fresh eye at stone tools turned up trees lower in the canopy. With this, together until they anive at a tree with at excavation sites. The important role Rousseau and Kendo, who had been monkeys. Then, as the chimps begin played by female Tal chimps in tool use watching from the ground, sped up into climbing nearby trees, they scatter as also raises the possibility that in the the trees and tried to grab them. Only a each pursues a different target. Goodall course of human evolution, - women may third of the weight of the chimps, how- gained the impression that Gombe have been decisive in the development ever, the monkeys managed to make it chimps boost their success by hunting of many of the sophisticated manipulat- to the next tree along branches too small independently but simultaneously,hereby t ive skills characteristic of our species. for their pursuers. But Falstaff had an- disorganizingtheir prey; our impressionis Tal mothers also appear to pass on their ticipated this move and was waiting for that the Tal chimps owe their success to skills by actively teaching their off- them. In the following confusion, Fal- being organizedthemselves. spring. We have observed mothers pro- staff seized a juvenile and killed it with Just why the Gombe and Tal chimps viding their young with hammers and a bite to the neck. As the chimps met in have developed such different hunting then stepping in to help when the inex- a rush on the ground, Falstaff began to strategies is difficult to explain, and we perienced youngsters encounter diffi- eat, sharing with Schubert and Rous- plan to spend some time at Gombe in culty. This help may include carefully seau. A juvenile colobus does not pro- the hope of finding out. In the mean- showing how to position the nut or hold vide much meat, however, and this time, time, the mere existence of differences the hammer properly. Such behavior has not all the chimps got a share. Frustrated is interesting enough and may perhaps never been observed at Gombe. individuals soon started off on another force changes in our understanding of Similarly, food sharing, for a long hunt, and relative calm returned fairly human evolution. Most currently ac- time said to be unique to humans, seems quickly: this sort of hunt, by a small cepted theories propose that some three more general in forest than in savanna band of chimps acting on their own at million years ago, a dramatic climate chimpanzees. Tal chimp mothers share the edge of their territory, does not gen- change in Africa east of the Rift Valley with their young up to 60 percent of the erate the kind of high excitement that turned dense forest into open, drier habi- nuts they open, at least until the latter prevails when more members of the tat. Adapting to the difficulties of life become sufficiently adept, generally at community are involved. under these new conditions, our ances- about six years old. They also share So far we have observed some 200 tors supposedly evolved into cooperative other foods acquired with tools, includ- monkey hunts and have concluded that hunters and began sharing food they ing honey, ants, and bone marrow. success requires a minimum of three caught. Supporters of this idea point out Gombe mothers share such foods much motivated hunters acting cooperatively. that plant and animal remains indicative less often, even with their infants. Tal 65 2 .:. PRIMATES chimps also share meat more frequently these forest chimpanzees? Africa's cines. Captive-bred chimps are avail- than do their Gombe relatives, some- tropical rain forests, and their inhabi- able, but they cost about twenty times times dividing a chunk up and giving tants, are threatened with extinction by more than wild-caught animals. Chimps portions away, sometimes simply allow- extensive logging, largely to provide the taken from the wild for these purposes ing. beggars to grab pieces. Western world with tropical timber and are generally young, their mothers hav- Any comparison between chimpan- such products as coffee, cocoa, and rnb- ing been shot during capture. For every zees and our hominid ancestors can only ber. Ivory Coast has lost 90 percent of chimp arriving at its sad destination, be suggestive,not definitive.But our stud- its original forest, and less than 5 per- nine others may well have died in the ies lead us to believe that the process of cent of the remainder can be considered forest or on the way.> Such priorities- hominization may have begun inde- pristine. The climate has changed dra- cheap coffee and cocoa and chimpan- pendently of the drying of the environ- matically. The harmattan, a cold, dry zees~o not do the economies of Third ment. Savanna life could even have wind from the Sahara previously un- World countries any good in the long delayed the process; many anthropologists known in the forest, has now swept run, and they bring suffering and death have been struck by how slowly homi- through the Tal forest every year since to innocent victims in the forest. Our nid-associated remains, such as the hand 1986. Rainfall has diminished; all the hope is that Brotus, Falstaff, and their ax, changed after their first appearance rivulets in our study region are now dry families will survive, and that we and in the Olduvai age. for several months of the year. others will have the opportunity to learn Will we have the time to discover In addition, the chimpanzee, biologi- about them well into the future. But more about the hunting strategiesor other, cally very close to humans, is in demand there is no denying that modem times perhaps as yet undiscovered abilities of for research on AIDS and hepatitis vac- work against them and us. 66
"Dim Forest_ Bright Chimps"