Reconciliation and post-conflict third-party affiliation among wild chimpanzees in the Mahale Mountains,Tanzania

This study investigated post-conflict (PC) behavior among wild chimpanzees (Pan troglodytes) of the M-group in the Mahale Mountains, Tanzania, and examined what types of behavior characterize the PC situation in this group, and the factors that influence the occurrence of PC affiliation between opponents soon after the end of an aggressive conflict (i.e., reconciliation). We found that the opponents affiliated selectively soon after the end of aggression, suggesting that reconciliation occurred in this group. The mean individual corrected conciliatory tendency (CCT) (Veenema et al. 1994 in Behav Proc 31:29–38) was 14.4%, which is similar to or lower than frequencies observed in studies of captive and wild chimpanzees. The valuable relationship hypothesis predicts that the CCT is higher among individuals who share valuable relationships (e.g., males or affiliative dyads) than among individuals who do not (e.g., females or less-associative dyads). However, the analysis based on data for aggression between unrelated individuals (including one incident between an adult and non-adult) and aggression between unrelated adults, did not uncover this difference. Affiliation by a previously uninvolved individual with the victim (consolation) and with the aggressor (appeasement) occurred more frequently following aggression than in the control condition. The results are compared with previous studies of captive and wild chimpanzees.     

Aggression toward large carnivores by wild chimpanzees of Mahale Mountains National Park, Tanzania

In the Mahale Mountains National Park of Tanzania, a group of about 33 chimpanzees were observed to surround a leopard den containing a mother and at least one cub and to drag out and kill the cub. This is the first report of chimpanzees or any other primate species killing their potential predator's offspring. The incident suggests that chimpanzees, without any weapons, can manage to defend themselves against a carnivore of at least up to leopard size, and implicates how the early hominids may have reacted against their potential predators.     

A preliminary note on the intestinal parasites of wild chimpanzees in the Mahale Mountains,Tanzania

Feces of wild chimpanzees in the Mahale Mountains, Tanzania, were inspected for intestinal parasites under a compound microscope. Eggs or larvae ofOesophagostomum, Strongyloides, Trichuris, Prosthenorchis, andBertiella were found. Intestinal nematodes significantly increased in the mid-rainy season. This finding supports (or, at least, is not in conflict with) the hypothesis thatAspilia leaves which are occasionally swallowed by chimpanzees may function as a vermicide, since ingestion of such leaves also increases significantly in the mid-rainy season.     

Prevalence of muzzle-rubbing and hand-rubbing behavior in wild chimpanzees in Mahale Mountains National Park, Tanzania

In 1998, four chimpanzees in the Mahale Mountains National Park, Tanzania, were observed wiping their mouths with non-detached leaves or stalks of grass, or rubbing their mouths with a tree trunk or branch, especially while eating lemons. The number of mouth-wiping/rubbing individuals increased to 18 in 1999. By 2005, 29 chimpanzees were documented wiping/rubbing their muzzles in this way. Although it is difficult to determine whether the chimpanzees acquired this behavior as a result of trial and error or social learning, the fact that chimpanzees at other sites perform this behavior with detached leaves or leafy twigs much more often than with intact items suggests the possibility that cleaning with intact plant parts at Mahale spread via social learning.     

Newly acquired feeding habits among the chimpanzees of the Mahale Mountains National Park,Tanzania

The M group chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains National Park, Tanzania, began to feed on three agricultural fruit species, guava, mango and lemon. It took them 7–8 years until they began to taste these fruits since the villagers left the park area in 1974. Although adult chimpanzees are conservative in their feeding habits, they are capable of rapidly acquiring new feeding habits, or new traditions, once they notice that the food is suitable.     

Dominance among male chimpanzees in the Mahale Mountains National Park,Tanzania: A preliminary study

Dominance relationships among male chimpanzees in the Mahale Mountains National Park, Tanzania, were analyzed. Although all adolescent males were unequivocally subordinate to all adult males, dominance relationships within the age classes were much less clear. Especially among adolescent males, few pant-grunts or agonistic interactions occurred. While adolescent males frequently pant-grunted at adult males, these latter males, except the alpha and the youngest, rarely pant-grunted to one another. This suggests that a difference of social status exists between adolescent and adult males. Adult males rarely display overt dominance to one another probably because the presence of other males affects their interactions. Moreover, they seem to try to keep their dominance relationship ambiguous when making it overt is not advantageous to them. This may be a political way for males to coexist with one another in a unit-group.     

Sex and group differences in feeding on animals by wild chimpanzees in the Mahale Mountains National Park,Tanzania

Sex differences in animal prey intake were revealed by fecal analysis among wild chimpanzees of the large-sized M-group (ca. 100 members) in the Mahale Mountains National Park, Tanzania: prime adult or old males feed more on vertebrates, while adult females more onCamponotus ants. By contrast, such differences were not obvious in the neighboring, small-sized K-group (ca. 20–30 members), despite the similar environment in which the two unit-groups lived. Such sex and group differences may be explained in terms of various factors, either ecological or social, or both, but social factors seem most responsible in particular for the group differences. It seems likely that increased capture rate of vertebrates per unit-group in the larger-sized M-group results in increased per capita intake of meat among prime adult or old males. Also, the more frequent interactions among prime adult or old males of M-group appear to reduce the frequency of theirCamponotus ant-fishing behavior.     

One observed case of temporary adoption of an infant by unrelated nulliparous females among wild chimpanzees in the Mahale Mountains,Tanzania

A 2.4-year-old male chimpanzee in the Mahale Mountains, Tanzania became separated from his mother probably because of contagion of the flu-like sickness. He was adopted alternately by two unrelated immigrant females for at least six days before he was reunited with his mother. This episode is described and analyzed in relation to the babysitter relationships among female chimpanzees. The adaptive significance of the babysitting behavior of nulliparous females is discussed.     

Seasonal trends in intestinal nematode infection and medicinal plant use among chimpanzees in the Mahale Mountains, Tanzania

A longitudinal study of nematode infection in chimpanzees was conducted between 1989 and 1994 on the M group chimpanzees of the Mahale Mountains National Park, Tanzania during two annual dry and rainy season periods and a third rainy season. Chemical and physical antiparasite properties of medicinal plant use against the strongyle nematodeOesophagostomum stephanostomum have recently been reported at Mahale. Here, the incidence of nematode infections were analyzed for seasonal trends to elucidate the possible influence of parasite infection on previously reported seasonality of medicinal plant use and to test the hypothesis that the use of these plants is stimulated byO. stephanostomum. The number of chimpanzees infected byO. stephanostomum was significantly higher in the rainy season than in the dry season of both 1989–1990 and 1991–1992. However, the incidence ofTrichuris trichura andStrongyloides fuelleborni showed no seasonality. Reinfection of individuals byO. stephanostomum occurred in synchrony with annual variation in rainfall: there was a sharp rise in the occurrence of new infections per individual within one to two months after the beginning of the first heavy rains of the season. This pattern coincides with the reproductive cycle of this nematode species.O. stephanostomum (95%) infections were associated significantly more frequently with medicinal plant use than eitherT. trichiura (50%) orS. fuelleborni (40%) infections. These observations are consistent with previous reports for the increased use of these plants during the rainy season and are consistent the hypothesis that medicinal plant use is stimulated byO. stephanostomum infection.     

Body weights of wild chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains National Park, Tanzania

Ten male and nine female habituated chimpanzees (Pan troglodytes schweinfurthii) in the Kasoje area of the Mahale Mountains National Park, Tanzania, were weighed intermittently between December 1973 and March 1980 by luring them up a rope hung on a spring balance: six adult males averaged 42.0 kg and eight adult females 35.2 kg. Seasonal change in body weight was recognized at least partially; body weights tended to decrease in the later part of the wet season presumably because of food shortage in the middle of the wet season. Comparison of body weight among three populations of the same subspecies suggests that adult female chimpanzees of Mahale appear to be heavier than those of the Gombe National Park, Tanzania, and that they seem to be similar to the forest-living counterparts of eastern Zaire. On the other hand, body weights of adult male chimpanzees from the three populations do not show significant differences. Perhaps feeding competition among adult females in a small, isolated habitat is more severe than that among adult males, which may result in the body weight reduction among adult female chimpanzees at Gombe.     

Association,ranging, and the social unit in chimpanzees of the Mahale Mountains,Tanzania

In order to characterize the social unit in chimpanzees, about which several conflicting views have been proposed, the proximity matrix among 55 recognized chimpanzees and the range covered by each of them are examined, on the basis of data obtained at the Mahale Mountains during 12 months in 1978–1979. It is shown once again that chimpanzees have a bisexual social unit (unit-group). Two such unit-groups were detected in the study area. All animals belonged to one of the two unit-groups except a few cycling females (and a juvenile male accompanied by his cycling mother) which were seen to associate alternately with members of two neighboring unit-groups, covering a whole range of one or even two unit-groups. The problem of such females is discussed in relation to the spatial relationships between the two unit-groups. Reexamining the membership of a unit-group, it is demonstrated that a unit-group was most likely patrilineal. While nulliparous females transferred between unit-groups, parous females tended to remain in a unit-group where they first gave birth to infants and to have several offspring therein. This appeared significant for ensuring recruitment of members of the next generation to a patrilineal unit-group. Although some adult males left their natal unit-group, they never joined the other. Male departure from a unit-group seemed to be forced by the other males and to be the sociological equivalent of going into exile, which is unique in nonhuman primates.     

Social play of juvenile and adolescent chimpanzees in the Mahale Mountains National Park,Tanzania

Social play of juvenile and adolescent chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains National Park, Tanzania, was studied, by analyzing processes of play and interindividual relationships in play. The results are discussed in relation to communication mechanisms. Play was initiated in several ways. Communication about play seems to depend on the receiver's interpretation: They can interpret the sender's behavior as play, referring to (1) play signals accompanied by the behavior, (2) transformation of the behavior in timing, strength, or rhythm, and (3) situation of the occurrence. Initiation attempts sometimes failed because one hesitated in playing with the other. Although the stronger often reduced his/her activity during play, play tended to escalate in activity. Players may enjoy such escalation. Play also had a mechanism not to escalate into fighting. Play was influenced by individuals other than the players. The third party's movement often affected the players' interaction. The term play does not indicate a behavior itself but the context of the behavior: The players interpret their behaviors in their play context.     

Food transfer between mother and infant chimpanzees of the Mahale Mountains National Park,Tanzania

We studied food transfer between chimpanzee mothers and infants in the Mahale Mountains National Park, Tanzania. The rate of infant solicitation for food dramatically increased in the second year of life, then gradually decreased and, in the seventh year, virtually disappeared. The pattern of the ontogeny of food sharing precisely followed that of solicitation because mothers shared food only when requested to do so by their infants. The success rate of solicitation, however, did not display extreme changes across ages. Food that was difficult to process was shared more frequently because it was more likely to be demanded by infants. We defined food retrieval as an infant’s recovery of leftovers discarded by its mother. Food types retrieved were often those that are difficult to process and were also likely to be shared by mothers. However, infants tended to solicit small, difficult food types for sharing while they often retrieved the remains of large, difficult food types. The function of food sharing and food retrieval lies in an infant’s learning food types that it cannot easily obtain or process by itself. The level of competition for food between mothers and infants remained low throughout infancy. We noted no particular characteristic about foods from which infants were displaced by mothers. As infants grew older, they increased the distance between themselves and mothers that became more aggressive.     

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.     

Dynamics of the temporal structures of playing clusters and cliques among wild chimpanzees in Mahale Mountains National Park

The overall structure and temporally changing configuration of members of social play among the wild chimpanzees (Pan troglodytes schweinfurthii) of Mahale Mountains National Park, Tanzania, were described on both the microscopic ‘clique’ levels, conceptualized as directly connected configurations through social play behavior, and macroscopic ‘cluster’ levels, conceptualized as indirectly connected gatherings of members of adjacent multiple cliques at the same time and space. Most playing clusters started as dyads. Although the cumulative number of participants increased, each clique size remained at 2 for most of the observational units. Dyadic cliques were more stable and lasted longer than larger cliques. Of all clusters’ playing fields, 64.7 % had maximum diameters of 3 m. In summary, chimpanzees played stably in dyadic pairs in most of the time. As time passed, other chimpanzees often joined in the playing groups to form large polyadic clusters. Even when all chimpanzees in a cluster played socially at the same time, they normally did so in separate dyadic pairs, forming multiple dyadic cliques simultaneously in a small space. These social play dynamics may be explained assuming a hypothesis based on a balance model among socially playing chimpanzees, as the balanced cliques are limited only to those in which all the existing pairs form the mutual dyads, and they tend to avoid unbalanced and maintain balanced relationships during social play. As a result, larger cliques were difficult to maintain for long periods and tended to transition into dyadic mutual cliques. Thus, Heider’s balance theory can be one of the possible theories to explain not only human social phenomena, but also the proximate mechanism of the structure and the temporal change of social play among wild chimpanzees. Although both mutual and transitive relationships are known to be balanced in various human networks, only mutual relationships among socially playing chimpanzees were balanced.     

One observed case of cannibalism among wild chimpanzees of the Mahale mountains

This paper presents a detailed report on the behavior of cannibalism observed in a group of wild chimpanzees of Western Tanzania for two days of January 13 and 14, 1977. This case differs from the other ones observed so far in that the adult males killed and ate an infant of their own group. Much interesting behavior was observed in the mother whose infant was eaten and the high-ranking males who killed and ate it.     

Geochemistry and clay mineralogy of termite mound soil and the role of geophagy in chimpanzees of the Mahale Mountains,Tanzania

Earth from a termite mound in the Mahale Mountains National Park, Tanzania, eaten by chimpanzees, was analyzed to determine the possible stimulus, or stimuli, for geophagy. The termite mound sample contains relatively high aluminum (10.0%), iron (3.0%), and sodium (0.5%). This correlates well with the mineralogy of the clay (<2 μm) fraction, which is high in metahalloysite, a 1:1 (Si:Al=1:1) clay mineral similar in chemical composition to the clay mineral kaolinite, and smectite (montmorillonite), which is a 2:1 expandable clay mineral. The combination of metahalloysite and smectite produces a substance much like the pharmaceutical Kaopectate^™ widely used by humans as an anti-diarrheal agent. These analyses and preliminary observations linking geophagy with instances of severe diarrhea, and other signs of gastrointestinal upset in the Mahale chimpanzees, suggest that one function for the ingestion of this substance by chimpanzees may be to help provide temporary relief from gastrointestinal ailments. Further detailed investigations into the relationship between health and geophagy should provide important insights into the diverse roles of this behavior as a form of self-medication.     

Female life history and mating patterns among the M group chimpanzees of the Mahale national park,Tanzania

The mating behavior of receptive females in the M group chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains, western Tanzania, was studied by intensive sampling over a period of 5 months. Restrictive matings were observed only between parous females mostly in the ovulatory stage and prime adult males, in particular the alpha. Young, nulliparous and/or non-ovulatory females tended to mate with immature or low-ranking adult males. By contrast, older, parous and/or ovulatory females tended to mate with adult and higher-ranking males. These confirmed the results of a previous extensive study of the same group. In addition, gradual shift from opportunistic to restrictive matings after inter-unit-group transfer was revealed for 2 ex-K-group parous females. The findings were discussed in relation to the life history of female chimpanzees. A National Park since 1984.     

Physiological activities and the active constituents of potentially medicinal plants used by wild chimpanzees of the Mahale mountains,Tanzania

Potential medicinal plants for wild chimpanzees have been studied in order to discover their physiologically active compounds. Tests of the physiological activity of 3 plant species—Vernonia amygdalina, Aspilia mossambicensis, andFicus exasperata—indicate that they contain a variety of active compounds. From one species,V. amygdalina, an antitumor agent and 2 possible antitumor promoters are identified. Furthermore, steroid glucosides were isolated as the bitter substances. These structurally new compounds are expected to exhibit a number of significant physiological activities. The chemical investigation of possible medicinal plants used by chimpanzees should be helpful in recovering naturally occurring compounds of medicinal significance for human use.     

Parasitology of five primates in Mahale Mountains National Park, Tanzania

Parasitological surveillance in primates has been performed using coprological observation and identification of specimens from chimpanzees (Pan troglodytes schweinfurthii) in Mahale Mountains National Park, Tanzania (Mahale). In this study, we conducted coprological surveillance to identify the fauna of parasite infection in five primate species in Mahale: red colobus (Procolobus badius tephrosceles), red-tailed monkeys (Cercopithecus ascanius schmidti), vervet monkeys (Cercopithecus aethiops pygerythrus), yellow baboons (Papio cynocephalus), and chimpanzees. Fecal samples were examined microscopically, and parasite identification was based on the morphology of cysts, eggs, larvae, and adult worms. Three nematodes (Oesophagostomum spp., Strongyloides sp., and Trichuris sp.), Entamoeba coli, and Entamoeba spp. were found in all five primate species. The following infections were identified: Bertiella studeri was found in chimpanzees and yellow baboons; Balantidium coli was found in yellow baboons; three nematodes (Streptopharagus, Primasubulura, an undetermined genus of Spirurina) and Dicrocoeliidae gen. sp. were found in red-tailed monkeys, vervet monkeys, and yellow baboons; Chitwoodspirura sp. was newly identified in red colobus and red-tailed monkeys; Probstmayria gombensis and Troglocorys cava were newly identified in chimpanzees, together with Troglodytella abrassarti; and Enterobius sp. was newly identified in red colobus. The parasitological data reported for red colobus, vervet monkeys, and yellow baboons in Mahale are the first reports for these species.