Innovation in wild chimpanzees (Pan troglodytes)

Innovations of behavior have major implications for the concept of culture in animals. Innovation has rarefy been documented in wild animal populations. The chimpanzees of the Taï National Park, Côte d’Ivoire, spontaneously included new patterns of behavior in their repertoire during our study. Some innovations were incorporated into a minority of the group members’ repertoire, whereas others, such as building day nests in trees and on the ground more frequently, became general behaviors. Similarly, new contexts for use of leaf- clipping behavior and novel ways of feeding on some leaves appeared and rapidly became part of the behavior of most group members. The environmental parameters were too stable to explain these new forms of behavior, as most of them took place within 1 month during the same dry season. In a similar way, leaf- grooming acquired a new function in Gombe chimpanzees. A process similar to social conventions could explain the emergence of these new functions for an existing behavior in a way rather similar to human “fashion. ” Three major characteristics of human culture — the absence of individual variations in the performance of the behavior, the general use of the behavior by group members, and the ability to modify the function of a behavior — characterize leaf-clipping in Taï chimpanzees and leaf- grooming in Gombe chimpanzees.     

Social grooming and play behavior of a captive group of chimpanzees

Aspects of the social grooming and play behavior of a group of six adolescent and young adult chimpanzees are contrasted and compared. Eleven months’ data indicate that older chimpanzees groomed more and played less than younger individuals. This transition period occurred earlier for females than males. Grooming behavior appeared to vary with reproductive state. A positive correlation was found between the estrous condition of cycling females and the amount of grooming that they received from the males. A mother of a young infant received particularly high levels of grooming from the other group members. Less variation among individuals was found for frequencies of play as compared to grooming. Play dropped following the death of one individual and was entirely inhibited for three weeks following the group’s transfer to a new environment and the reintroduction of a former group member. Comparison to a free-ranging population indicates important differences in both frequencies and general patterns of play and grooming.     

Variation over Time in Parasite Prevalence Among Free-ranging Chimpanzees at Gombe National Park,Tanzania

From January to September, 2005, we collected fecal samples from 60 chimpanzees at Gombe National Park, Tanzania and examined them for parasites. We compared current parasite prevalence data with previous studies to obtain a pattern of parasitism over time. There were considerable similarities in the parasite species composition and prevalence, although we noted some variations. Generally, parasite prevalence decreased over time, with the present prevalence being lower than in previous surveys. We identified 8 types of parasites, all of which had previously been documented in the chimpanzees of Gombe. Three nematodes — Oesophagostomum sp., Strongyloides fulleborni, and Abbreviata caucassica— occurred at higher prevalence (41.2–45.5%) but relatively lower than previous findings of 50–91%. We also diagnosed unidentified strongyles at a moderate prevalence (33%), lower than a previous record of 41%. Probstmayria gombensis occurred at relatively low prevalence (16.4%) vs. past observations (23–59%), while the prevalence of Trichuris sp. (7.3%) was closely similar to previous records of 5–9%. We also observed unidentified ciliate at 9% within the same range as in previous studies (5–28%). The prevalence of Troglodytella abrassarti was 78%, closely similar to previous findings of 75%. There was no significant variation in parasite prevalence between chimpanzees of the Kasekela community and those of the Mitumba community, although the former tended to have higher prevalence of helminths than the latter. The causes of the similarities and variations in parasite prevalence over time are discussed. The study provides baseline data for monitoring of chimpanzee health at Gombe.     

Alpha male chimpanzee grooming patterns: implications for dominance “style”

In social primates, individuals use various tactics to compete for dominance rank. Grooming, displays and contact aggression are common components of a male chimpanzee's dominance repertoire. The optimal combination of these behaviors is likely to differ among males with individuals exhibiting a dominance “style” that reflects their tendency to use cooperative and/or agonistic dominance tactics. Here, we examine the grooming behavior of three alpha male chimpanzees at Gombe National Park, Tanzania. We found that (1) these males differed significantly in their tendency to groom with other males; (2) each male's grooming patterns remained consistent before, during and after his tenure as alpha, and (3) the three males tended to groom with high‐ middle‐ and low‐ranking partners equally. We suggest that body mass may be one possible determinant of differences in grooming behavior. The largest male exhibited the lowest overall grooming rates, whereas the smallest male spent the most time grooming others. This is probably because large males are more effective at physically intimidating subordinates. To achieve alpha status, a small male may need to compensate for reduced size by investing more time and energy in grooming, thereby ensuring coalitionary support from others. Rates of contact aggression and charging displays conformed to this prediction, suggesting that each male exhibited a different dominance “style.” Am. J. Primatol. 71:136–144, 2009. © 2008 Wiley‐Liss, Inc.     

Tool use and tool making in wild chimpanzees

Reported incidences of tool use and tool making for three wild chimpanzee populations increase from Mahale (12 and 3 types of use and making, respectively), Gombe (16 and 3) to Ta? (19 and 6). Sticks are commonly used and prepared at all three sites. However, Ta? chimpanzees seem to perform more modifications on the material before using it. They are also the only chimpanzees seen to pound objects with tools and to combine two different tool uses to get access to one food item. Tool making is the rule for abundant material (grass, twigs), but appears to be rarer for scarce, hard material (clubs, stones). Factors involved in the acquisition and the benefit of tool use are discussed along with factors affecting the frequency and complexity of tool making in chimpanzees.     

Anxiety-related behavior of orphan chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania

This study examined the anxiety levels and social interactions of two orphan and four mother-reared adolescent chimpanzees (Pan troglodytes schweinfurthii) in the Kasekela community at Gombe National Park, Tanzania. We used focal sampling in the field at Gombe to observe these adolescent individuals. Their social interactions and anxious behavior, measured as rough scratching, were recorded. The two orphans differed from others of a similar age by exhibiting higher levels of anxiety and lower levels of play. These results suggest that a mother’s absence, even in naturalistic conditions in which other members of the community are available to the orphan, may have long-lasting impact on an adolescent’s anxiety and its ability to engage in complex social interactions, such as play.     

Skeletal evidence of trauma in African apes, with special reference to the gombe chimpanzees

Incidence of cranial and postcranial skeletal trauma was investigated in samples of chimpanzees (Pan troglodytes troglodytes, P. troglodytes schweinfurthii), lowland gorillas (Gorilla gorilla gorilla), and bonobos (P. paniscus). The larger (adult) samples of chimpanzees (N=127 crania, 92 postcrania) and gorillas (N=136 crania, 62 postcrania) are curated at the Powell-Cotton Museum, Birchington, U.K. The bonobo collection (N=71 crania, 15 postcrania) is housed the Musée Royal de l'Afrique Centrale in Tervuren, Belgium. In addition, data were collected on the small but extremely well-documented skeletal sample from Gombe National Park (N=14 crania, 13 postcrania — including adults and adolescents). Cranial injuries, including healed fractures and bite wounds, were fairly frequent in the museum collection of chimpanzees (5.5% of individuals), but were twice as frequent in gorillas (11.0%). In the Gombe sample an even higher incidence was observed (28.6% of individuals). Bonobos, however, showed the lowest incidence of cranial trauma found among any of the African ape samples (1.4% of individuals). Postcranial trauma, documented most clearly by healed fractures, was seen in 21.7% of the Powell-Cotton chimpanzees, 30.8% of Gombe chimpanzees, 17.7% of gorillas, and in 13.3% of bonobos. Most of these lesions were found in the upper appendage. Nevertheless, highly debilitating healed fractures of the femur were also noted, most frequently and severe in female gorillas. The pattern of injuries suggests serious risks of falling in all free-ranging African apes, but also (in chimpanzees and gorillas) considerable risk from interindividual aggression, especially for males.     

Mortality rates among wild chimpanzees

In order to compare evolved human and chimpanzees' life histories we present a synthetic life table for free-living chimpanzees, derived from data collected in five study populations (Gombe, Ta?, Kibale, Mahale, Bossou). The combined data from all populations represent 3711 chimpanzee years at risk and 278 deaths. Males show higher mortality than females and data suggest some inter-site variation in mortality. Despite this variation, however, wild chimpanzees generally have a life expectancy at birth of less than 15 years and mean adult lifespan (after sexual maturity) is only about 15 years. This is considerably lower survival than that reported for chimpanzees in zoos or captive breeding colonies, or that measured among modern human hunter-gatherers. The low mortality rate of human foragers relative to chimpanzees in the early adult years may partially explain why humans have evolved to senesce later than chimpanzees, and have a longer juvenile period.     

Skeletal pathology in Pan troglodytes schweinfurthii in Kibale National Park, Uganda

The ecological pressures shaping chimpanzee anatomy and behavior are the subject of much discussion in primatology and paleoanthropology, yet empirical data on fundamental parameters including body size, morbidity, and mortality are rare for wild chimpanzees. Here, we present skeletal pathology and body size data for 20 (19 crania, 12 postcrania) chimpanzees (Pan troglodytes schweinfurthii) from Kibale National Park, Uganda. We compare these data with other East African populations, especially Gombe National Park. Estimated body size for Kibale chimpanzees was similar to other East African populations and significantly larger than Gombe chimpanzees. The high rates of trauma and other skeletal pathology evident in the Kibale chimpanzee skeletons were similar to those in the Gombe skeletal sample. Much of the major skeletal trauma in the Kibale skeletons was attributable to falls, although other pathologies were noted as well, including apparent injuries from snares, degenerative arthritis, and minor congenital abnormalities.     

Responses of wild chimpanzees (<Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis>) toward seismic aftershocks in the Mahale Mountains National Park,Tanzania

This is the first report documenting the responses of wild chimpanzees (Pan troglodytes schweinfurthii) to seismic activities. During our long-term fieldwork in Mahale Mountains National Park, Tanzania, a high-intensity earthquake with a Richter magnitude of 6.8 occurred at 15:19 hours local time on 5 December 2005. During the main tremor, the chimpanzees displayed the “wraa” call, “scream,” and “pant bark” or “bark” vocalizations. Many mild aftershocks followed the main tremor, and the wild chimpanzees displayed a variety of responses to these. In several cases, they climbed trees or stopped activities such as grooming, moving, and feeding. These responses are similar to those previously reported in nonhuman primates. During the observations, a unique behavior, one never reported before was exhibited by a female chimpanzee. She placed her right palm on the ground giving the impression she was inspecting the trembling of the ground.     

Seed Reingestion in Savannah Chimpanzees (<Emphasis Type="Italic">Pan troglodytes verus</Emphasis>) at Fongoli,Senegal

Coprophagy is common in captive primates but has also been reported in the wild. For example, wild apes extract and reingest items from faeces. We term this behavior seed reingestion because the dung matrix is not consumed. We assessed the importance of seed reingestion in a population of savannah chimpanzees at Fongoli, southeastern Senegal, one of the hottest and driest areas of the species’ range, where chimpanzees have a relatively narrow dietary repertoire. We observed habituated chimpanzees on 122 d during 8 mo in 2005 and 2006, employing both focal subject and scan sampling of identified individuals for 1278 h of data collection. Chimpanzees reingested seeds of 2 species: Parkia biglobosa and Adansonia digitata. Both seed species have a hard protective shell, and the embryos are rich in proteins and lipids. Chimpanzees initially ate the fruit matrix pulp and swallowed intact seeds before reingesting and chewing/destroying seeds. Seed reingestion accounted for almost 2% of feeding time. We suggest that at Fongoli this behavior may be an adaptive strategy to maximize food intake, by softening the seed’s shell and making the seed’s content more accessible.     

Is human conversation more efficient than chimpanzee grooming?

Clique sizes for chimpanzee (Pan troglodytes) grooming and for human conversation are compared in order to test Robin Dunbar’s hypothesis that human language is almost three times as efficient a bonding mechanism as primate grooming. Recalculation of the data provided by Dunbar et al. (1995) reveals that the average clique size for human conversation is 2.72 whereas that of chimpanzee grooming is shown to be 2.18. The efficiency of human conversation and actual chimpanzee grooming over Dunbar’s primate grooming model (always one-to-one and a one-way interaction) is 1.27 and 1.25, respectively, when we take role alternation into account. Chimpanzees can obtain about the same efficiency as humans in terms of quantity of social interactions because their grooming is often mutual and polyadic. The fieldwork was supported by a grant from the International Scientific Research Program (07041138 to T. Nishida) of the Monbusho (Japanese Ministry of Education, Science, Sports, and Culture). Michio Nakamura is a research fellow at Japan Monkey Centre. He received his Master of Science degree from Kyoto University in 1996. He is carrying out research on the grooming behavior of chimpanzees at Mahale, Tanzania, for his doctorate.     

Predation on mammals by chimpanzees in the montane forest of Kahuzi, Zaire

The rate of predation on mammals by chimpanzees was determined from carcasses and from fecal specimens found on fresh trails during a 16-month period in the montane forest of Kahuzi-Biega National Park, Zaire. A unit-group of semi-habituated chimpanzees, composed of 22 – 23 individuals including 8 adult or adolescent males, appeared to kill about 18 – 30 mammalian prey (16 – 28Cercopithecus monkeys) per year, if the multiple kills by chimpanzees were not considered. A juvenile l'Hoest's monkey was recorded for the first time as the prey of chimpanzees in this study. Predation occurred in the late dry and the early rainy seasons, when the diversity of ripe fruits was the highest during the year. The Kahuzi chimpanzees tended to kill mammals less frequently but to killCercopithecus monkeys more frequently than chimpanzees in other habitats. The absence of red colobus monkeys, which are the most frequent prey in Gombe, Mahale, and Tai, might be responsible for the low predation rate. However, the estimated rate of predation onCercopithecus monkeys is the highest record among various chimpanzee habitats. At least 11 – 18% of theCercopithecus population seemed to be lost annually as a result of being killed by chimpanzees. Chimpanzees may be the most important predators on these monkeys in the absence of leopards at Kahuzi. The examination of fecal samples and carcasses suggested that adult (probably male) or adolescent chimpanzees tended to eat juvenile or subadult monkeys most frequently, as is also seen for chimpanzees in Gombe, Mahale, and Tai.     

Grooming and the Expectation of Reciprocation in Mandrills (<Emphasis Type="Italic">Mandrillus sphinx</Emphasis>)

It is often (implicitly) assumed that the expectation of reciprocation motivates animal altruism, and thus that animals “plan” their social interactions. We tested this hypothesis by studying a captive group of mandrills (Mandrillus sphinx). In our focal group, the alpha male was more likely to provide agonistic support in the minutes after the receipt of grooming than in the absence of previous grooming. This offered other group members the possibility of manipulating the male’s support by grooming him before engaging in an aggression. We used survival analysis to test the hypothesis that the other group members systematically groomed the alpha male just before engaging in aggression, which would suggest that the expectation of reciprocation motivated their grooming. Contrary to the prediction of our hypothesis, we found that other group members did not groom the alpha male just before engaging in aggression, and thus did not benefit from increased support from the most effective ally. These results suggest that mandrills do not plan their social interactions and that the expectation of reciprocation does not motivate them to groom.     

The foraging adaptation of chimpanzees,and the recent behaviors of the provisioned apes in Gombe and Mahale National Parks,Tanzania

Current understandings of chimpanzee behavior and social organization are based largely on twenty years of studies of provisioned chimpanzees in Gombe and Mahale National Parks. These data indicate that chimpanzees are aggressive, dominance-seeking and fiercely territorial. Reports from a number of naturalistic (nonprovisioning, unobtrusive) field studies contrast sharply. All report open groups of nonaggressive, nonhierarchical chimpanzees, which repeatedly fission for foraging and reunite as a larger social group. Because of the authority accorded the Mahale and Gombe reports, the naturalistic studies are often discounted. In this paper foraging theory is used to show that the recent behaviors of the artificially fed apes are maladaptive, while those of the nonprovisioned, wild chimpanzees are excellent foraging strategy. It is suggested, but not concluded, that the recent behaviors of the Gombe and Mahale chimpanzees may be frustration-induced responses to feeding methods which introduce a blockage between the apes and the desirable bait foods.     

Social grooming among wild bonobos (Pan paniscus) at Wamba in the Luo Scientific Reserve, DR Congo, with special reference to the formation of grooming gatherings

Chimpanzees (Pan troglodytes) groom in gatherings in which many individuals may be connected via multiple chains of grooming and they often exchange partners with each other. They sometimes groom another while receiving grooming; that is, one animal can play two roles (i.e., groomer and groomee) simultaneously. Although this feature of chimpanzees is notable from the viewpoint of the evolution of human sociality, information on our other closest living relative, the bonobo (Pan paniscus), is still lacking. In this study, I describe grooming interactions of bonobos at Wamba in the Luo Scientific Reserve, Democratic Republic of the Congo (DR Congo), with a particular focus on the formation of grooming gatherings. Like chimpanzees, the bonobos also performed mutual grooming (two individuals grooming each other simultaneously) and polyadic grooming (three or more individuals). However, unlike chimpanzees, these sessions lasted for only a short time. Bonobos rarely groomed another while receiving grooming. Because social grooming occurred not only in trees but also in open spaces, including treefall gaps, the conditions did not necessarily limit the opportunity to make multiple chains of grooming. However, bonobos also engaged in social grooming in different ways from chimpanzees; That is, many individuals were involved simultaneously at a site, in which they separated for dyadic grooming. Some cases clearly showed that bonobos preferred a third party not to join while grooming in a dyad, suggesting that bonobos have a preference for grooming in dyads and that immature individuals formed the preference that was shared among adults while growing up. Most members of the study group ranged together during the majority of the study period. Although bonobos show a fission–fusion grouping pattern, when group members frequently encounter one another on a daily basis, they may not be motivated to form multiple grooming chains at this site, as do chimpanzees.     

Population dynamics of wild chimpanzees at Bossou,Guinea, between 1976 and 1983

The population dynamics of a small group of wild chimpanzees at Bossou, Guinea, were studied during a 6.5-year period between 1976 and 1983. The natality rate (0.23 births/female/year) was higher and the interbirth interval (4.3–4.4 years/female) was shorter than those of chimpanzees at East African study sites (the Gombe and Mahale National Parks). The infant mortality for the first 3 years (0.06–0.18/year) was lower than those in East Africa. However, the population had remained almost stable since 1967 (growth rate: 0.985/year). The increase in number by births was offset by the disappearance (perhaps emigration) of adolescent chimpanzees. Adult males immigrated and disappeared (perhaps emigrated) but adult females rarely did.     

Predatory behavior among wild chimpanzees of the mahale mountains

Eighteen predatory and two cannibalistic episodes have been observed among wild chimpanzees of the Mahale Mountains. The prey consists mainly of juveniles of medium-sized mammals, six species of which were recorded as prey fauna for the first time in this study. Predatory behavior of Mahale chimpanzees seems more opportunistic and primitive than has ever been observed in the Gombe National Park in terms of capture technique, size of prey, co-operation in hunting, sexual difference in capture frequency, degree of consumption and extent of meat sharing. Cannibalism is an inter-unit-group phenomenon and may be an extension of infanticide, which may function in changing “mother” into “female.” This study was financed mainly by the Overseas Scientific Research Fund of the Ministry of Education, Japan and partly by the Japan International Co-operation Agency and the Ministry of Natural Resources and Tourism, Tanzania.     

Responses of chimpanzees to a recently dead community member at Gombe National Park, Tanzania

Chimpanzee responses to the death of a group member have rarely been observed in the wild and most instances involve infant deaths. One of the very few detailed accounts of a group's response to the death of an adult community member is from Gombe National Park, Tanzania, where Teleki [Folia Primatologica 20:81-94, 1973] observed the responses of 16 chimpanzees to an accidental death, none of whom touched the body. Now, almost 40 years later, we report on the behaviors of 16 (different) Gombe individuals to the recently dead body of an adult female community member. In stark contrast to Teleki's account, we observed individual chimpanzees' responses to range from curious observation and passive investigation (e.g. smelling and grooming) to the shaking, dragging, and frustrated beating of the body. Variation across demographic groups is described and may reflect individuals' past experience with death. The implications of our observations are discussed in the context of core morbidity traits shared between humans and chimpanzees.