“Stepping-sticks” and “seat-sticks”: New types of tools used by wild chimpanzees (Pan troglodytes) in Sierra Leone

In Tenkere, Sierra Leone, a community of wild chimpanzees (Pan troglodytes verus) spent long hours eating the fruits and flowers of the Kapok (Ceiba pentandra) tree. The branches of this species are covered in sharp thorns which make movement in their high canopies problematic for the chimpanzees. In an apparent attempt to increase their mobility and to ease the discomfort of lengthy bouts of eating in these trees, some of the Tenkere chimpanzees have been observed using stick tools as foot (“stepping-sticks”) and body (“seat-sticks”) protection against the painful thorns. This form of tool-using is culturally unique to the Tenkere chimpanzees, as at other sites where these apes have been observed eating parts of kapok trees, there are no published records of this tool technology. In three of the stepping-stick tool use incidents, the chimpanzee used the tool(s), held between their greater and lesser toes, in locomotion. This form of tool use is the first recorded case of habitually used tools that can be justifiably categorized as being “worn” by any known wild population of Pan troglodytes. Am J Primatol 41:45–52, 1997. © 1997 Wiley-Liss, Inc.     

Using the Tools at Hand: Manual Laterality and Elementary Technology in Cebus spp. and Pan spp.

Cebus and Pan appear to be a remarkable example of evolutionary convergence in behavioral ecology. We examine their apparently analogous solutions to problems posed by laterality of hand function and elementary technology. We scrutinize appropriate published data in a meta-analysis, focusing on Cebus apella and C. capucinus and on Pan paniscus and P. troglodytes. We compare behavioral data in terms of captive versus wild, and tool use versus non-tool use, but notable gaps exist in the data, especially for bonobos. Cebus and Pan spp. are equivalent tool users in captivity, but chimpanzees are notably more extensively so in nature. For hand preference, captive bonobos and wild and captive chimpanzees show ambipreference for non-tool-use patterns. For both Cebus spp. and Pan spp., there is a tendency for individuals to be committed exclusively to one hand or the other for tool use. The data for laterality of hand function fit consistently into the five-level model proposed by McGrew and Marchant (1996).     

Flexible and Persistent Tool-using Strategies in Honey-gathering by Wild Chimpanzees

Several populations of wild chimpanzees use tools to raid bee nests, but preliminary observations of chimpanzees in the Congo Basin indicate that they may have developed sophisticated technical solutions to gather honey that differ from those of apes in other regions. Despite the lack of habituated groups within the range of the central subspecies, there have been several reports of different types of tools used by chimpanzees to open beehives and gather honey. Researchers have observed some of these behaviors (honey dipping) in populations of western and eastern chimpanzees, whereas others (hive pounding) may be limited to this region. Toward evaluating hypotheses of regional tool using patterns, we provide the first repeated direct observations and systematic documentation of tool use in honey-gathering by a population of Pan troglodytes troglodytes. Between 2002 and 2006, we observed 40 episodes of tool use in honey-gathering by chimpanzees in the Goualougo Triangle, Republic of Congo. Pounding was the most common and successful strategy to open beehives. Chimpanzees at this site used several tools in a single tool-using episode and could also attribute multiple functions to a single tool. They exhibited flexibility in responses toward progress in opening a hive and hierarchical structuring of tool sequences. Our results support suggestions of regional tool using traditions in honey-gathering, which could be shaped by variation in bee ecology across the chimpanzee range. Further, we suggest that these chimpanzees may have an enhanced propensity to use tool sets that could be related to other aspects of their tool repertoire. Clearly, there is still much to be learned about the behavioral diversity of chimpanzees residing within the Congo Basin.     

Tool-set for termite-fishing and honey extraction by wild chimpanzees in the Lossi Forest, Congo

The use of perforating sticks and flexible stalks in combination for termite fishing and a complex tool-set of three components used sequentially (stout chiel, bodkin, and dip-stick) to penetrate melipone and ground-dwelling bee hives byPan troglodytes troglodytes are documented or, inferred from circumstantial evidence. Functionally, termite extraction tools were similar to other locations in west and central Africa, but the plants and the number of raw material species used were different. Tools varied in the degree of modification (fraying ends). Chimpanzees in the Lossi forest seem to be able to use the tools not in a stereotyped fashion, but in a flexible, insightful way. The extraction of Melipone honey using large pieces of wood as pounding tools has rarely been recorded elsewhere. The most impressive technological solution to the honey-getting problem by wild chimpanzees was shown by this study. This is the only known, use of a tool-set of three components in sequence to extract honey by wild chimpanzees.     

Complex tool sets for honey extraction among chimpanzees in Loango National Park, Gabon

Homo faber was once proposed as a label for humans specifically to highlight their unique propensity for tool use. However, new observations on complex tool use by the chimpanzees of Loango National Park, Gabon, expand our knowledge about tool-using abilities in Pan troglodytes. Chimpanzees in Loango, when using tools to extract honey from three types of bee nests, were observed to regularly use three- to five-element tool sets. In other words, different types of tools were used sequentially to access a single food source. Such tool sets included multi-function tools that present typical wear for two distinct uses. In addition, chimpanzees exploited underground bee nests and used ground-perforating tools to locate nest chambers that were not visible from the ground surface. These new observations concur with others from Central African chimpanzees to highlight the importance of honey extraction in arguments favoring the emergence of complex tool use in hominoids, including different tool types, expanded tool sets, multifunction tools, and the exploitation of underground resources. This last technique requires sophisticated cognitive abilities concerning unseen objects. A sequential analysis reveals a higher level of complexity in honey extraction than previously proposed for nut cracking or hunting tools, and compares with some technologies attributed to early hominins from the Early and Middle Stone Age. A better understanding of similarities in human and chimpanzee tool use will allow for a greater understanding of tool-using skills that are uniquely human.     

Chimpanzee ‘folk physics’: bringing failures into focus

Differences between individuals are the raw material from which theories of the evolution and ontogeny of cognition are built. For example, when 4-year-old children pass a test requiring them to communicate the content of another''s falsely held belief, while 3-year-olds fail, we know that something must change over the course of the third year of life. In the search for what develops or evolves, the typical route is to probe the extents and limits of successful individuals'' ability. Another is to focus on those that failed, and find out what difference or lack prevented them from passing the task. Recent research in developmental psychology has harnessed individual differences to illuminate the cognitive mechanisms that emerge to enable success. We apply this approach to explaining some of the failures made by chimpanzees when using tools to solve problems. Twelve of 16 chimpanzees failed to discriminate between a complete and a broken tool when, after being set down, the ends of the broken one were aligned in front of them. There was a correlation between performance on this aligned task and another in which after being set down, the centre of both tools was covered, suggesting that the limiting factor was not the representation of connection, but memory or attention. Some chimpanzees that passed the aligned task passed a task in which the location of the broken tool was never visible but had to be inferred.     

Tool-use to obtain honey by chimpanzees at Bulindi: new record from Uganda

Honey-gathering from bee nests has been recorded at chimpanzee (Pan troglodytes) study sites across tropical Africa. Different populations employ different strategies, ranging from simple ‘smash-and grab’ raids to use of sophisticated tool-sets, i.e., two or more types of tool used sequentially in a single task. In this paper I present evidence of tool-use, and the probable use of a tool-set, for honey-gathering by unhabituated chimpanzees at Bulindi, a forest–farm mosaic south of the Budongo Forest in Uganda. Between June and December 2007, 44 stick tools were found in association with 16 holes dug in the ground, corresponding to the period when stingless bees (Meliponula sp.) appeared in chimpanzee dung. In 11 cases the confirmed target was a Meliponula ground nest. Two potential tool types were distinguished: digging sticks encrusted with soil, and more slender and/or flexible sticks largely devoid of soil that may have functioned to probe the bees’ narrow entry tubes. Reports of chimpanzees using tools to dig for honey have been largely confined to Central Africa. Honey-digging has not previously been reported for Ugandan chimpanzees. Similarly, use of a tool-set to obtain honey has thus far been described for wild chimpanzee populations only in Central Africa. Evidence strongly suggests that Bulindi chimpanzees also use sticks in predation on carpenter bee (Xylocopa sp.) nests, perhaps as probes to locate honey or to disable adult bees. These preliminary findings from Bulindi add to our understanding of chimpanzee technological and cultural variation. However, unprotected forests at Bulindi and elsewhere in the region are currently severely threatened by commercial logging and clearance for farming. Populations with potentially unique behavioral and technological repertoires are being lost.     

Use of leaves as cushions to sit on wet ground by wild chimpanzees

A new type of tool use, leaf cushion, by wild chimpanzees (Pan troglodytes verus) at Bossou, Guinea, was found. We report two cases: one is indirect evidence; the other is direct observation of a chimpanzee who used the tool. Both cases indicate that chimpanzees used a set of leaves as a cushion while sitting on wet ground. Chimpanzees at Bossou show various kinds of tool use, some of which are unique to the community. Most of these behavioral patterns are subsistence tool use for obtaining food, as at other study sites. The use of leaves as a cushion adds to the few instances of nonsubsistence, elementary technology seen used by wild chimpanzees. Am. J. Primatol. 44:215–220, 1998. © 1998 Wiley-Liss, Inc.     

Tool use by wild chimpanzees (Pan troglodytes) to obtain termites (Macrotermes herus) in the Mahale Mountains,Tanzania

Wild chimpanzees (Pan troglodytes) used probes made of vegetation to fish for termites (Macrotermes herus) in the Mahale Mountains of western Tanzania. Data on both the artefacts and behavior associated with their use were recorded over a 5-month period. The chimpanzees of one unit group, B Group, were seen four times to use the tools to extract the insects from their mounds. A sample of 290 tools was collected and analyzed in terms of age, seasonality, length, width, class of raw materials, species, methods of making, extent of use, and damage incurred through use. There were differences across groups in tool use in feeding on termites; some could be related to biotic factors, but others appeared to be cultural differences.     

Behavioral and functional strategies during tool use tasks in bonobos

Different primate species have developed extensive capacities for grasping and manipulating objects. However, the manual abilities of primates remain poorly known from a dynamic point of view. The aim of the present study was to quantify the functional and behavioral strategies used by captive bonobos (Pan paniscus) during tool use tasks. The study was conducted on eight captive bonobos which we observed during two tool use tasks: food extraction from a large piece of wood and food recovery from a maze. We focused on grasping postures, in‐hand movements, the sequences of grasp postures used that have not been studied in bonobos, and the kind of tools selected. Bonobos used a great variety of grasping postures during both tool use tasks. They were capable of in‐hand movement, demonstrated complex sequences of contacts, and showed more dynamic manipulation during the maze task than during the extraction task. They arrived on the location of the task with the tool already modified and used different kinds of tools according to the task. We also observed individual manual strategies. Bonobos were thus able to develop in‐hand movements similar to humans and chimpanzees, demonstrated dynamic manipulation, and they responded to task constraints by selecting and modifying tools appropriately, usually before they started the tasks. These results show the necessity to quantify object manipulation in different species to better understand their real manual specificities, which is essential to reconstruct the evolution of primate manual abilities.     

Drinking tools of wild chimpanzees at Bossou

Use of drinking tools by wild chimpanzees (Pan troglodytes) and the context in which the tools were used were studied at Bossou, Republic of Guinea, West Africa. During the middle to late dry season and early wet season liquids are available occasionally in the holes of trees. Chimpanzees drank water or sap using a leaf (or fiber) as a sponge or spoon. When the chimpanzees were on the ground, they tended to use one of a few kinds of soft, hairless leaves, if they were available nearby. Females, particularly juveniles and adolescents, were thought to be the main users of the drinking tool. In a few episodes, a tool set was used to procure liquid. Once a chimpanzee used a stick to push a leaf sponge into a water hole and to pull it out from the hole. In addition, three chimpanzees used a pestle to squeeze sap from an oil-palm tree before using a fiber sponge. © 1995 Wiley-Liss, Inc.     

Dietary responses to fruit scarcity of wild chimpanzees at Bossou,Guinea: Possible implications for ecological importance of tool use

A 13-month ecological study was conducted at Bossou, Guinea, West Africa, to elucidate how a community of wild chimpanzees (Pan troglodytes verus) deals with the scarcity of main foods. During the study period, fruit availability fluctuated radically. The chimpanzees were confirmed to depend heavily on three “keystone resources” which were available when their main foods (fruit pulp) were scarce. These were fruits of Musanga cecropioides, oil-palm (Elaeis guineensis) nuts, and oil-palm pith. These are abundant in the chimpanzees' home range and their nutritional contents compensate for a decrease in nutritional intake from fruit pulp. The presence of these excellent backup foods may explain the high reproductive performance of Bossou chimpanzees. Here, chimpanzees consumed two of the three keystone foods using two types of tool behavior: nut-cracking for oil-palm nuts and pestle-pounding for oil-palm pith. These tool-using behaviors accounted for 31.9% of the total feeding time spent in June (the month in which the highest frequency occurred) and 10.4% in total for the year. It is suggested that the Bossou chimpanzees depend strongly on tools for their subsistence. This implies a possible function for tool technology in the evolution of our human ancestors. Am J Phys Anthropol 106:283–295, 1998. © 1998 Wiley-Liss, Inc.     

Pestle-pounding behavior of wild chimpanzees at Bossou,Guinea: A newly observed tool-using behavior

A new type of tool-using behavior was observed in a group of wild chimpanzees (Pan troglodytes verus) at Bossou, Guinea. The chimpanzees used the leaf-petiole of oil-palm trees (Elaeis guineensis) as a pounding tool to deepen a hole in the oil-palm crown which appeared after the chimpanzees had pulled out the central young shoots. Finally, the chimpanzees extracted and ate the apical meristem or apical bud of the oil-palm tree which is edible but inaccessible without such tool use. The motor pattern which the chimpanzees employed is similar to that used for termite-nest digging but it is more exaggerated and requires great force. The behavior is reminiscent of pestlepounding. The chimpanzees exploit substantial amounts of food with this tool-using skill, compensating for insufficient fruit foods in the primary forest. This tool-using behavior was first observed in 1990 and, to date, almost half of the group members have been confirmed to use the pestle tool. It appears that this tool-using behavior was invented recently and has since spread widely throughout the group as a habitual one.     

Reproductive Parameters of Female<Emphasis Type="Italic">Pan paniscus</Emphasis> and <Emphasis Type="Italic">P. troglodytes</Emphasis>: Quality versus Quantity

We investigated intra- and interspecific differences in life history and reproductive parameters in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We compare the parameters of wild and captive females in order to shed light on the influence of habitat or specific differences or both on reproduction. We present new and additional information on reproductive parameters from captive bonobos and chimpanzees. Captive chimpanzees birth more live offspring and have a shorter interbirth interval, but experience higher infant mortality than captive bonobos. Although captive bonobo females tend to start reproduction at a younger age than chimpanzees, this is effectively only so for wild-born females of both species. Ultimately both species reach the same rate of production of offspring surviving to 5 yr. These results contrast with data from the wild. Wild bonobos tend to have higher reproductive success, a higher fertility rate and a shorter interbirth interval than wild chimpanzees. Reproduction is similar for wild and captive bonobos, which suggests that they are producing at their maximum under both conditions. Overall captive chimpanzees perform better than their wild conspecifics, probably because of lower feeding competition. Infant survival is the only specific difference not affected by captivity. Bonobo infants survive better, which suggests that chimpanzee infants are more at risk. We argue that the interspecific variation in reproductive parameters in captivity is related to the different influence of captivity on reproduction and different pressures of external sources of infant and juvenile mortality.     

Chimpanzees are more skilful in competitive than in cooperative cognitive tasks

In a series of four experiments, chimpanzees, Pan troglodytes, were given two cognitive tasks, an object choice task and a discrimination task (based on location), each in the context of either cooperation or competition. In both tasks chimpanzees performed more skilfully when competing than when cooperating, with some evidence that competition with conspecifics was especially facilitatory in the discrimination location task. This is the first study to demonstrate a facilitative cognitive effect for competition in a single experimental paradigm. We suggest that chimpanzee cognitive evolution is best understood in its socioecological context.     

Ant-dipping among the chimpanzees of Bossou,Guinea, and some comparisons with other sites

We present a detailed study of ant‐dipping among the wild chimpanzees (Pan troglodytes verus) of Bossou, in southeastern Guinea, West Africa. Observations suggest a strong influence of prey (Dorylusspp.) characteristics, including aggressiveness and/or gregariousness, on tool length and technique employed by the chimpanzees. Bossou chimpanzees exhibit two ant‐dipping techniques: 1) direct mouthing, and 2) pull‐through. In addition, they were observed dipping for several species of Dorylus ants, classed into two categories: Red and Black. Tool length was longer when dipping in higher‐risk contexts, i.e., at the ants' nest site or on Black ants. The pull‐through technique was almost exclusively associated with dipping at the nest site. This latter technique was associated with tools over 50cm long, whereas direct mouthing was the only technique observed with tools <50cm long. Our experimental findings, together with our observations on the behavior of the chimpanzees, suggest that at the nest, the pull‐through technique was a more efficient technique than direct mouthing. We review our results in the context of ant‐dipping observed at two other long‐term chimpanzee study sites, i.e., Gombe (Tanzania) and Taï (Côte d'Ivoire), where differences in tool length, technique used, and focal Dorylus ant species have been reported. Finally, we urge similar detailed studies of this tool‐use behavior in both Gombe and Taï to shed further light upon our results and their implications. Am. J. Primatol. 58:133–148, 2002. © 2002 Wiley‐Liss, Inc.     

Do chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>) use cleavers and anvils to fracture <Emphasis Type="Italic">Treculia africana</Emphasis> fruits? Preliminary data on a new form of percussive technology

Wild chimpanzees (Pan troglodytes) are renowned for their use of tools in activities ranging from foraging to social interactions. Different populations across Africa vary in their tool use repertoires, giving rise to cultural variation. We report a new type of percussive technology in food processing by chimpanzees in the Nimba Mountains, Guinea: Treculia fracturing. Chimpanzees appear to use stone and wooden “cleavers” as tools, as well as stone outcrop “anvils” as substrate to fracture the large and fibrous fruits of Treculia africana, a rare but prized food source. This newly described form of percussive technology is distinctive, as the apparent aim is not to extract an embedded food item, as is the case in nut cracking, baobab smashing, or pestle pounding, but rather to reduce a large food item to manageably sized pieces. Furthermore, these preliminary data provide the first evidence of chimpanzees using two types of percussive technology for the same purpose.     

Transport of Functionally Appropriate Tools by Capuchin Monkeys (Cebus apella)

Capuchin monkeys (Cebus sp.) are notable among New World monkeys for their widespread use of tools. Like chimpanzees, they use both hammer tools and insertion tools in the wild to acquire food that would be unobtainable otherwise. Recent evidence indicates that capuchins transport stones to anvil sites and use the most functionally efficient stones to crack nuts. We further investigated capuchins’ assessment of functionality by testing their ability to select a tool that was appropriate for two different tool‐use tasks: A stone for a hammer task and a stick for an insertion task. To select the appropriate tools, the monkeys investigated a baited tool‐use apparatus (insertion or hammer), traveled to a location in their enclosure where they could no longer see the apparatus, made a selection between two tools (stick or stone), and then could transport the tool back to the apparatus to obtain a walnut. We incorporated tool transport and the lack of a visual cue into the design to assess willingness to transport the tools and the monkeys’ memory for the proper tool. Six brown capuchins (Cebus apella) were first trained to select and use the appropriate tool for each apparatus. Four animals completed training and were then tested by allowing them to view a baited apparatus and then travel to a location 8 m distant where they could select a tool while out of view of the apparatus. All four monkeys chose the correct tool significantly more than expected and transported the tools back to the apparatus. Results confirm capuchins’ propensity for transporting tools, demonstrate their capacity to select the functionally appropriate tool for two different tool‐use tasks, and indicate that they can retain the memory of the correct choice during a travel time of several seconds.     

Design complexity in termite-fishing tools of chimpanzees (Pan troglodytes)

Adopting the approach taken with New Caledonian crows (Corvus moneduloides), we present evidence of design complexity in one of the termite-fishing tools of chimpanzees (Pan troglodytes) in the Goualougo Triangle, Republic of Congo. Prior to termite fishing, chimpanzees applied a set of deliberate, distinguishable actions to modify herb stems to fashion a brush-tipped probe, which is different from the form of fishing tools used by chimpanzees in East and West Africa. This means that ‘brush-tipped fishing probes’, unlike ‘brush sticks’, are not a by-product of use but a deliberate design feature absent in other chimpanzee populations. The specialized modifications to prepare the tool for termite fishing, measures taken to repair non-functional brushes and appropriate orientation of the modified end suggest that these wild chimpanzees are attentive to tool modifications. We also conducted experimental trials that showed that a brush-tipped probe is more effective in gathering insects than an unmodified fishing probe. Based on these findings, we suggest that chimpanzees in the Congo Basin have developed an improved fishing probe design.     

Behavioral diversity in populations of free-ranging chimpanzees in Africa: is it culture?

Behavioral differences exist among populations of wild chimpanzees (Pan troglodytes, Hominoidea) across Africa. Deciding if these are cross-cultural differences demands careful interpretation and rigorous scrutiny. Even standard patterns like social grooming may show variation in detail between neighboring populations. Some patterns of tool use, such as using hammers to crack nuts, also vary across far western Africa. At least 37 populations of free-ranging chimpanzees show tool use, and 14 show at least one habitual pattern of tool use. Regional differences exist among the three subspecies or geographical races of chimpanzees. Convincing empirical demonstration of social customs and traditions in non-human species is problematical, and even something so simple in principle as innovation is hard to show in practice. However, culture need not depend on imitation, teaching, or language, either in humans or in other species.