Nut cracking by wild chimpanzees in Sierra Leone, West Africa

Abstract

ABSTRACT. I report an incidence of chimpanzee (Pan troglodytes verus) cracking of Detarium senegalense (Caesalpiniaceae) At 16:35 chimps were observed leaving the area. The group included two adult females (one with a moderate sexual swelling, ca. 7 cm), one subadult or adult female, one medium size juvenile of indeterminate sex, and two large infants or small juveniles of indeterminate sex (one of these was carried piggyback by an adult female).Upon close investigation of the location at which the chimps were first detected, I found numerous (ca. 100) freshly opened pods of Detarium senegalense (Caesalpiniaceae) scattered in an area about 10 m in diameter. This area was directly beneath the crown of a largeDetarium. The majority of the freshly opened pods were clustered around three large, broad surface roots which were freshly scarred.Detarium senegalense trees are not uncommon (about 0.15 individuals per hectare within the two main study areas on Tiwai Island) but are wid.ely scattered as individual trees throughout the forest. The fruits are composed of a single seeded disc-shaped pod 5 to 6 cm in diameter and I to 1.5 cm thick. The pod wall is extremely hard (ca. 2 mm thick); I could 1) Tiwai Island (7~ ll~ is a large (ca. 10 km 2) river island in the Moa river in southwestern Sierra Leone. open pods only with the aid of a hammer. The seed is large (ca. 5 • 1 cm) artd, like the pod, disc-shaped. When mature, the pod wall is covered with a thick fibrous pulp making the entire fruit ca. 5 to 6 cm long and ca. 4 cm thick. After the fruit drops from the tree, the pulp decays in two to four months leaving only the pod wall and its contained seed. Fruits on the ground for several months with little or no pulp remaining appear to be those selected by chimps for cracking.The nuts opened by chimps are characterized by being broken transversely across the disc (Fig. 1). Bush pigs (Potamochoerus porcus) also occasionally eat Detarium seeds, but they apparently open the nuts with their teeth by splitting the pods laterally along the suture line.Because the chimps were not observed opening the nuts, their cracking method is not known. However, when the chimps were observed leaving the area, they were not carrying stones. I found no stones in the immediate area that may have been used for nut cracking. Three other methods seem plausible: (1) placing the nut on a surface root anvil and striking it with a stick; (2) same method as above, but using a second Detarium nut in lieu of a stick; and (3) holding the nut to be cracked in the hand, and then striking it directly on the surface root anvil. Of these, the third seems least likely due to both the hardness of the nuts and the volume of noise produced (cracking a nut by holding it in the hand would tend to muffle the noise). BozscH and BOESCH (1983) observed chimps in the Ivory Coast open fruits of Strychnos aculeata (Loganiaceae) by holding them in the hartd and banging them against a hard surface, but they only report tool use for cracking Detarium nuts.The most likely...

Primate archaeology reveals cultural transmission in wild chimpanzees (Pan troglodytes verus)

“…So far only chimpanzees and humans have been found to converge on the behaviour variant that is most common in the group, even if they have alternative behaviours in their individual repertoires that accomplish the same goal just as efficiently [67]. Conformist transmission has been proposed to restrict the accumulation of traditions in non-human [27,37,49] and human [62,68] populations. Therefore, local differences between populations remain despite individual exchange through marriage and migration [69], preventing cross cultural homogenization but protecting cultural diversity among neighbouring communities.…”

“…Chimpanzees in the wild are known to use natural stone and wooden hammers to crack open various nut species [14,30,[36][37][38][39][40]. Nut-cracking is a classic percussion behaviour whereby a nut is placed on a hard surface and a hammer is used to pound it until the nut breaks open.…”

Acquisition of Nut-Cracking Behaviour by 2 Capuchin Monkeys (Cebus apella)

“…Nut-cracking behaviour has been directly observed in several populations of chimpan zees [Boesch and Boesch, 1981, 1983, 1984Sugiyama and Roman, 1979;Sugiyama, 1981;Whitesides, 1985], and some studies have been conducted on the acquisition and dissemination of this behaviour both in a captive group [Sumita et al, 1985] and in captive chimpanzees released on a natural island in Liberia [Hannah and McGrew, 1987], Data on wild chimpanzees show that 'the ontogenesis of nut cracking is a longerlasting process than that of the other tool techniques used by chimpanzees' that are acquired years earlier [Boesch and Boesch, 1984, p.436]. Furthermore, Beck [1980, p. 100] notes that nut-cracking has rarely been reported for captive chimpanzees.…”

4,300-Year-old chimpanzee sites and the origins of percussive stone technology

“…T ool use among modern wild ape populations, first reported in the early 19th century (1), has been documented throughout tropical Africa, and chimpanzees from West Africa are known for their use of stone tools for nut cracking (2)(3)(4)(5)(6). In 2002, the publication of recent buried remains of unintentionally fractured stone left behind by modern chimpanzees from Côte d'Ivoire outlined the potential of using archaeological methods in cultural primatological research and also identified the type of material assemblage that would allow archaeologists to detect and characterize ancient chimpanzee nut-cracking behavior.…”