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Dim Forest_ Bright Chimps

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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-

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                                                                                                 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.




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