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.     

Trauma, degenerative disease, and other pathologies among the Gombe chimpanzees

The well-known and extremely well-documented chimpanzees from Gombe National Park were analyzed for presence of skeletal pathologies. Of the 15 animals available for study, 11 were old and complete enough to permit systematic analysis. Of these, 10 showed some evidence of skeletal pathological involvement. The most common type of lesion seen resulted from trauma. Those chimps with the most fractures (Old Female, 3; Flo, 4; Hugo, 8) are consistently the oldest individuals in the sample. In addition to accidental falls, the most common cause of trauma was from interpersonal violence, resulting in bite wounds (see in two individuals) and fractures (see in three individuals). Conversely to trauma, degenerative disease was exceedingly rare in this population, found in no large intervertebral joints (N = 344) and only two major synovial joints (N = 186). In fact, the complete lack of osteophytosis, even in older individuals, stands in stark contrast to the situation seen in modern humans, perhaps in our species reflecting a biomechanical cost of bipedality.     

Anogenital swelling in pregnant chimpanzees of Gombe National Park

Previous studies show that anogenital swelling patterns of pregnant chimpanzees in captivity are correlated with the female's age during pregnancy and are associated with changes in social behavior. The purpose of the present study was to investigate whether the anogenital swelling patterns of free-ranging pregnant chimpanzees resemble those reported for captive chimpanzees. We reviewed the records of 47 pregnancies experienced by 20 female chimpanzees living in Gombe National Park from 1975 to 1992. Percentage scores for swelling during each trimester and for the overall occurrence of various levels of swelling were obtained by dividing the frequency by the total number of days the subject was observed (i.e., 28 days of swelling/165 days observation = 17.2% anogenital swelling for that pregnancy). Subjects exhibited anogenital swelling an average of 25.1% of the days observed during pregnancy, yet reached maximum only 9.4% of the time. Anogenital swelling occurred less frequently as pregnancy progressed, averaging 40.8, 27.3, and 2.7% in the first, second, and third trimesters, respectively. As seen in captive chimpanzees, young pregnant females at Gombe showed anogenital swelling more often than did older ones (r = ?.65, P < .0001). These findings are consistent with reports of behavior associated with anogenital swelling (e.g., intercommunity transfer of young females exhibiting anogenital swelling). © 1993 Wiley-Liss, Inc.     

Polymerase chain reaction detection of Clostridium perfringens in feces from captive and wild chimpanzees, Pan troglodytes

Background For veterinary management of non‐human primates in captivity, and conservation of wild‐living primates, management of their health risks is necessary. Incidences of pathogenic bacteria in the fecal specimens are considered as one of the useful indicators for non‐invasive health monitoring. Methods We carried out the detection of Clostridium perfringens in feces from captive and wild chimpanzees by the rapid polymerase chain reaction method. Results The bacterium was detected in most fecal specimens (80%) in captive chimpanzees. Contrarily, the detection rate in the wild chimpanzees was low, with 23% (n = 12) of 53 fecal samples from the Bossou group, Guinea, and 1.2% (1/81) in the Mahale group, Tanzania. Conclusions These results show that the intestinal microflora differs between Pan populations under various living conditions, being influenced by their diet and environment.     

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.     

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.     

Troop fission in free-ranging baboons in the Gombe Stream National Park, Tanzania.

During a 13 month field study of baboons in the Gombe Stream National Park, Tanzania, the troop under observation divided into two groups. One group left the main troop to become ultimately an independent troop with a separate range. The troop fission followed a period of instability in the male status hierarchy. The events prior to and during the troop fission are described in detail and the membership of the group which left is analyzed. Social bonds prior to the fission, including kinship, determined membership in the group which left. Aggression from members of the main troop played a major role in causing the group which left to establish a new range. This fission is compared with troop fissions observed in rhesus and Japances macaques.     

Severe Aggression Among Female Pan troglodytes schweinfurthii at Gombe National Park, Tanzania

Aggression is generally more severe between males than between females because males gain greater payoffs from escalated aggression. Males that successfully defeat rivals may greatly increase their access to fertile females. Because female reproductive success depends on long-term access to resources, competition between females is often sustained but low key because no single interaction leads to a high payoff. Nonetheless, escalated aggression can sometimes immediately improve a female’s reproductive success. Resisting new immigrants can reduce feeding competition, and infanticide of other females’ young can increase a female’s access to resources. East African chimpanzees live in fission-fusion communities in which females occupy overlapping core areas. Growing evidence indicates that reproductive success correlates with core area quality, and that females compete for long-term access to core areas. Here we document 5 new cases of severe female aggression in the context of such competition: 2 attacks by resident females on an immigrant female, a probable intracommunity infanticide, and 2 attacks on a female and her successive newborn infants by females whose core areas overlapped hers. The cases provide further evidence that females are occasionally as aggressive as males. Factors influencing the likelihood and severity of such attacks include rank and size differences and the presence of dependable allies. Counterstrategies to the threat of female aggression include withdrawing from others around the time of parturition and seeking male protection. We also discuss an unusual case of a female taking the newborn infant of another, possibly to protect it from a potentially infanticidal female.     

Analysis of a bone assemblage made by chimpanzees at Gombe National Park, Tanzania

Chimpanzee hunting provides information on prey characteristics and constraints acting on a large-bodied primate lacking a hunting technology, and has important implications for modeling hunting by fossil hominids. Analysis of the remains of five red colobus monkeys captured and consumed by Gombe chimpanzees in a single hunting bout provides one of the first opportunities to investigate the characteristics of prey bones surviving chimpanzee consumption. Four of the five individuals (an older infant, two juveniles and one subadult) were preserved in the bone assemblage; a neonate was entirely consumed. Cranial and mandibular fragments had the highest survivorships, followed by the scapulae and long bones. Post-cranial axial elements had the lowest survivorships. A high percentage (80%) of the long bones and ribs surviving consumption were damaged, most commonly through crenulation and step fracturing of bone ends. One of two partially reconstructed crania preserves a canine puncture through its left parietal. Proposed characteristics of faunal assemblages formed through chimpanzee-like hunting include small modal prey size, limited taxonomic diversity, a high proportion of immature individuals and a high frequency of skull bones. These characteristics would not uniquely identify hunting by fossil primates in the geological record, necessitating a contextual approach to diagnose hunting by hominids not forming an archeological record.Hominid utilization of vertebrate tissue is first unambiguously documented at 2.5 m.y.a. Rather than representing a strict "scavenging phase" in the evolution of hominid-prey interactions, Oldowan hominid carnivory may represent the overlay of large mammal scavenging on a tradition of small mammal hunting having a low archeological visibility.     

Patterns of food sharing among mother and infant chimpanzees at Gombe National Park, Tanzania

The patterns of food sharing among mother and infant chimpanzees at the Gombe National Park, Tanzania, are primarily influenced by the infants' ability to procure and process foods independently. Foods infants could find and process on their own were not shared by mothers as frequently as foods infants could not obtain independently. Temporal changes were observed in the patterns of interactions as infants matured. It is suggested that food sharing may be considered a behavioral strategy which facilitates the infant's transition from dependent suckling to independent foraging.     

Paleoepidemiology of a central California prehistoric population from CA-Ala-329: dental disease

Ala-329 is a prehistoric central California site located on the southeastern margin of San Francisco Bay, dating from approximately 500 AD up to pre-European contact. A large earth mound, Ala-329, has yielded many well preserved burials, approximately 300 of which are included in this study. The most common pathological lesions seen in this population are in the dentition. Advanced attrition is pervasive, affecting all individuals with teeth in occlusion for 2 years or more. Deciduous teeth are involved even in very young children and often show severe wear before replacement. In the permanent dentition, all elements are involved by the second decade; in the oldest age category (41+ years), all individuals show severe wear throughout their dentitions. In fact, by the end of the third decade, the majority of individuals have no enamel remaining. Mild periodontal involvement is found in 74% of adults, socket resorption in 53%, and abscesses in 31% of the relevant sample. Interestingly, although dental abscesses are found more than twice as often among males, socket resorption is seen more often among females. Dental caries are seen in only 10 individuals. The high incidence of periodontal remodeling, socket resorption, and dental abscesses is probably a secondary result of severe dental attrition. It is hypothesized that a large quantity of abrasives in the diet is responsible for the extreme degree of attrition, in fact, among the most severe for any population yet described.     

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.     

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.     

Demographic observations (1963–1973) on the chimpanzees of Gombe National Park, Tanzania

This report provides a longitudinal demographic profile for a small study population of chimpanzees living in the Gombe National Park of Tanzania, East Africa. The size and composition of this study population, and the trends in mortality, natality and migratory patterns it experienced over a span of ten years, are described and analysed within various ethological and ecological frameworks. The validity of the demographic profile is examined in relation to field methodology, as the study population was intensively provisioned with bananas for several years. The results yield some guidelines for managing and conserving wild chimpanzee populations, and special emphasis is placed upon protection from diseases that involve human vectors. The data presented here may also offer some novel insights to the evolution of pongid and hominid populations, so tentative steps are taken to place the Gombe profile into a broader demographic perspective.     

On the possible adaptive value of coprophagy in free-ranging chimpanzees

Coprophagy occurred during major periods of feeding on fruits of Dialium spp. (Caesalpiniaceae) in a group of orphaned chimpanzees released in Conkouati Douli National Park, Republic of Congo. Since stress, boredom or food scarcity could not explain coprophagy according to our daily behavioral and veterinary control observations, we suggest that Dialium seeds were the item of interest in the feces. Two types of Dialium seeds were commonly found in the feces after chimpanzees swallowed the mesocarp and whole seeds together. These seeds were either whole and hard or whole/broken and soft imbibed. A mechanical and/or chemical effect of the gut passage may enable the chimpanzees to chew and ingest the seeds, thus providing nutritional intake.     

New Cases of Intergroup Violence Among Chimpanzees in Gombe National Park,Tanzania

Despite considerable attention to chimpanzee intergroup violence, the number of observed cases remains small. We report 4 cases of intergroup violence that occurred in Gombe National Park, Tanzania, between 1993 and 2002. We observed (3 cases) or inferred (1 case) males from the Kasekela community to attack members of their 2 neighboring communities: Mitumba and Kalande. In 1993, Kasekela males killed and ate a female infant from Mitumba. In 1998, Kasekela males captured 2 infants (sex unknown) from Kalande, one of which escaped and the other was killed and eaten. Also in 1998, Kasekela males attacked an adolescent male from Kalande. The victim was alive but severely injured by the end of the attack. The intensity and duration of the attack are comparable to other attacks that resulted in fatal injuries. In 2002, observers found the body of an adolescent male from Mitumba following an incursion by Kasekela males into the area. The injuries inflicted on the Mitumba male together with circumstantial evidence suggest that Kasekela males killed him. The attacks support the view that intergroup violence is a persistent feature of chimpanzee societies and that the primary benefit attackers gain from them is reduced competition for resources.     

Notes on chimpanzee interactions with small carnivores in Gombe National Park,Tanzania

Although interspecific interactions between chimpanzees and various mammals have been reported from several field studies, relatively few encounters with carnivores of any size have been observed in natural conditions. The previously documented examples are here supplemented by three events describing wild chimpanzee responses to small carnivores. The observations now available suggest that chimpanzee responses are flexible rather than strictly patterned.     

Dental variability of the Liberian chimpanzee,Pan troglodytes verus

Dental variability was studied in a collection of Liberian chimpanzee (Pan troglodytes verus) crania from one geographic area of Central Liberia. Morphological and metric data were compared to another population of the same subspecies studied by Schuman and Brace (1955) as well as to other pongid taxa. It appears that of all living pongids, chimpanzees are the most derived in their lower molar patterns, particularly, P. t. verus. It is clear, however that the mandibular molar patterns of contemporary chimpanzees are more similar to other pongids that to humans which is contra to the suggestions of Schuman and Brace. Hypocone reduction from M1 to M3 is the common pattern in all hominoids. Complete absence of the M3 hypocone is rare in pongids but it is present in the Frankfurt collection. Of living pongids, the gorilla expresses the least amount of hypocone reduction from M1 to M3. A cusp of Carabelli is recorded bilaterally in one P.t. verus. There is less odontometric variation in P.t. verus than in other pongids as indicated by the CV’s which may suggest the greater dental variability present when different geographic groups are included in the sample.