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.     

Noninvasive paternity assignment in Gombe chimpanzees

The relative success of chimpanzee male mating strategies, the role of male dominance rank and the success of inbreeding avoidance behaviour can only be assessed when paternities are known. We report the probable paternities of 14 chimpanzees included in a long‐term behavioural study of chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania. DNA samples were collected noninvasively from shed hair and faeces and genotyped using 13–16 microsatellite loci characterized in humans. All 14 offspring could be assigned to fathers within the community. While there is a positive relationship between male rank and reproductive success, we demonstrate that a range of male mating strategies (possessiveness, opportunistic mating and consortships) can lead to paternity across all male ranks. Several adult females were at risk of breeding with close male relatives. Most successfully avoided close inbreeding but in one case a high‐ranking male in the community mated with his mother and produced an offspring. In contrast to recent data on chimpanzees (P. t. verus) from the Taï forest, Côte d’Ivoire, no evidence of extra‐group paternity was observed in our study. Reanalysis of Taï data using a likelihood approach casts doubt on the occurrence of extra‐group paternity in that community as well.     

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.     

Poliomyelitis and skeletal asymmetry in Gombe chimpanzees

Skeletons of free-ranging chimpanzees from Gombe National Park, Tanzania allow assessment of the effects of long-term, unilateral upper limb paralysis due to the infectious viral disease, poliomyelitis. Comparison of left and right upper limb bone weights, lengths, joint areas, and diaphysial diameters between two adult females with long-term, partial paralysis and a group of unaffected adult Gombe chimpanzees show that the disease caused considerable asymmetries in the skeleton. Detailed analyses of mineral content and diaphysial cross-sectional geometry of the humerus in the affected females show individual differences. The analysis extends to consideration of bone-muscle relationships and peripheral and central nervous system involvement. For each individual, sex, estimated age at death, and behavioral information during life are known from field studies. The impact of the disease on survival and reproductive outcome of the affected individuals is discussed.     

Causes of death in the Kasekela chimpanzees of Gombe National Park, Tanzania

Understanding the rates and causes of mortality in wild chimpanzee populations has important implications for a variety of fields, including wildlife conservation and human evolution. Because chimpanzees are long-lived, accurate mortality data requires very long-term studies. Here, we analyze 47 years of data on the Kasekela community in Gombe National Park. Community size fluctuated between 38 and 60, containing 60 individuals in 2006. From records on 220 chimpanzees and 130 deaths, we found that the most important cause of mortality in the Kasekela community was illness (58% of deaths with known cause), followed by intraspecific aggression (20% of deaths with known cause). Previous studies at other sites also found that illness was the primary cause of mortality and that some epidemic disease could be traced to humans. As at other study sites, most deaths due to illness occurred during epidemics, and the most common category of disease was respiratory. Intraspecific lethal aggression occurred within the community, including the killing of infants by both males and females, and among adult males during the course of dominance-related aggression. Aggression between communities resulted in the deaths of at least five adult males and two adult females in the Kasekela and Kahama communities. The frequency of intercommunity violence appears to vary considerably among sites and over time. Intercommunity lethal aggression involving the Kasekela community was observed most frequently during two periods. Other less common causes of death included injury, loss of mother, maternal disability, and poaching.     

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.     

Body size and proportions in chimpanzees,with special reference toPan troglodytes schweinfurthii from Gombe National Park,Tanzania

Body weight, cranial capacity, linear and joint area data from ten free-ranging adult chimpanzees from Gombe National Park, Tanzania with known life histories allow study of variation in a local population and comparison to other populations ofPan troglodytes and toPan paniscus. Because individuals in the Gombe population are small compared to other common chimpanzees, they provide a useful comparison toPan paniscus. Body weight and some linear dimensions overlap withPan paniscus. However, cranial capacity, tooth size, and body proportions of Gombe individuals lie within the range of otherPan troglodytes and are distinct fromPan paniscus.     

Rates of predation on mammals by gombe chimpanzees, 1972–1975

Rates of chimpanzee predation on mammals are calculated using data on 75 kills recorded during focal observation in Gombe National Park, Tanzania, from January 1972 to April 1975. The chimpanzees were members of two study communities (Kanyawara, or Northern, and Kahama, or Southern, community), and were observed as focal individuals for 14,583 hr by more than 30 researchers and field assistants working in pairs. The rate of predation by females was too low to allow reasonable estimates. For males, the mean rate of killing during the study period was 0.31 kills per male per 100 hr (N=17 males), or 4.65 kills per 100 hr in the two communities. In contrast to results from Mahale Mountains, there was no difference in predation rate between wet and dry seasons. However, predation rates varied over time, increasing by four times between the first three and last four seasons of the sample period. In an average year the 15 adult and subadult male chimpanzees are calculated to have killed 204 prey per year in an area of 16 km², varying between 99 and 420 prey per year in periods of low and high predation rate. Red colobus were the most frequent prey, followed by bushpig and bushbuck. Predation rates varied greatly on different prey species, and were not related to either the proportion of time spent within 200 m of male chimpanzees, or to their population densities. In relation to encounter rates and population density, baboons, blue monkeys, and redtail monkeys were killed at a fraction of the rate of red colobus monkeys, which suffered severe mortality from chimpanzee predation. Predation on bushpig and bushbuck also appears to have been high in relation to population density. The amount of food provided by predation is estimated to have averaged 600 kg per year for chimpanzees in the two communities (totalling 14–17 adult or subadult males, 18–20 adult of subadult females, and about 19 infants or juveniles). This suggests that adult males consumed around 25 kg of meat per year, although any average figure undoubtedly masks considerable individual variation. Present data suggest that chimpanzees in Gombe and Tai National Park, Ivory Coast, prey on mammals at rates higher than other populations.     

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.     

Infant killing and cannibalism in free-living chimpanzees

Male chimpanzees at the Gombe National Park were twice seen to attack 'stranger' females and seize their infants. One infant was then killed and partially eaten: the other was 'rescued' and carried by three different males. Once several males were found eating a freshly killed 'stranger' infant. A similar event was observed in Uganda by Dr. Suzuki and Dr. Nishida reports an incident from the Mahali Mountains, Tanzania. A different kind of killing occurred at Gombe when a female and her daughter killed and ate three infants of other females of the same community during a 2-year period. There is evidence suggesting that other infants may have died in this way. The paper draws attention to puzzling aspects of infant killing and cannibalism in chimpanzees.     

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.     

A demographic analysis of the membership of the American Society of Primatologists: 1992

Rank differences in the production of vocalizations by wild, semihabituated, unprovisioned chimpanzees were investigated during a 10-month study in the Kibale Forest, Uganda. Vocalization rates were calculated from data collected during 230 hours of focal-animal sampling on adult females, adult males, and subadult males. Rates were calculated according to whether individuals were alone, with adult females only, or in mixed parties, and the results were compared with published data collected at the Gombe provisioning area. Adult females and low-ranking adult and sub-adult males were generally quiet except when they were in mixed parties, whereas high-ranking males vocalized in all social contexts. These results were in partial contrast to data collected at Gombe, which indicated that vocal production was similar across all age and sex classes. Vocal production at Gombe did, however, resemble that from mixed parties at Kibale, suggesting that the provisioning area at Gombe was comparable to a natural socioecological context occurring at large fruiting trees. It is suggested that low-ranking chimpanzees refrain from loud vocalizing when they are alone or with females only in order to avoid attracting feeding competition and/or potentially aggressive males. These individuals may vocalize when they are associating with high-ranking males in order to advertise the presence of large parties and to deter other individuals from joining them. The use of loud, interparty calls by high-ranking males, when alone or with others, is consistent with the greater sociality of adult male chimpanzees. Loud calling might be advantageous for adult males in attracting mates or allies. © 1993 Wiley-Liss, Inc.     

Patterns of predation by chimpanzees on red colobus monkeys in gombe national park, 1982–1991

Predatory patterns in wild chimpanzees are important evidence in the continuing debate about the role of hunting in the behavior of early hominids. Data are presented on the predator–prey ecology of red colobus monkeys (Colobus badius tephrosceles) and chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania, from 1982 through 1991. During this period chimpanzees were observed to kill 429 mammalian prey items, 350 of which were red colobus. Hunts were undertaken by chimpanzees in 71.5% of encounters with red colobus, and in 52.2% of all hunts at least one colobus was caught. Hunting occurred in all months, but its frequency peaked in the late dry season months of August and September, and was lowest in the rainy months of April and May. There was greater seasonality of hunting from 1982 to 1991 than previously reported for Gombe. Hunting success varied between 40% in the rainy season and 65% in the dry season. Sixty multiple kills of colobus were reported in which from two to seven colobus were killed. Approximately 75% of all colobus caught were immatures; juveniles were the most preyed upon age class. Adult and adolescent male chimpanzees made 89.3% of all kills; the 10.7% of kills made by adult females was an increase over the 4% figure for female kills reported in the preceding decade. Hunting showed a strong “binge” tendency, with the explanation for binges likely related to social rather than ecological factors. These results are discussed in light of earlier hunting data for Gombe chimpanzees, and compared with data from other chimpanzee field studies. © 1994 Wiley-Liss, Inc.     

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.     

Response of Rhesus Macaques (Macaca mulatta) to the Body of a Group Member That Died from a Fatal Attack

Among animals that form social bonds, the death of a conspecific may be a significant social event, representing the loss of an ally and resulting in disruptions to the dominance hierarchy. Despite this potential biological importance, we have only limited knowledge of animals’ reactions to the death of a group member. This is particularly true of responses to dead adults, as most reports describe the responses of mothers to dead infants. Here, we describe in detail and provide video evidence of the behavioral responses of a group of free-ranging rhesus macaques (Macaca mulatta) immediately after the death of a mid-ranking adult male as a result of a fatal attack. High-ranking male members of the group, suspected to have carried out the attack, dragged and bit the dead body, exhibiting a rate of aggression 20 times greater than baseline levels. Lower-ranking individuals approached and inspected the body by looking closely, smelling, and grooming the fur. There was inconclusive evidence that these rhesus macaques found the death of a conspecific stressful: Levels of grooming between group members after the fatal attack were significantly higher than baseline levels, and higher than levels of grooming after nonfatal attacks. However, when grooming levels were adjusted based on the assumption that individuals positioned close to the body, i.e., those visible to researchers, were more likely to be engaged in grooming than those positioned farther away, this difference from baseline was no longer significant. The rate of self-directed behaviors after the fatal attack was also not different from baseline. Many of the behaviors we observed directed toward the body (aggression, inspection) have been previously reported in chimpanzees and geladas, and are similar to reactions sometimes displayed by humans. As such, this report represents a potentially valuable contribution the nascent field of nonhuman primate thanatology.     

Signature Patterns of MHC Diversity in Three Gombe Communities of Wild Chimpanzees Reflect Fitness in Reproduction and Immune Defense against SIVcpz

Major histocompatibility complex (MHC) class I molecules determine immune responses to viral infections. These polymorphic cell-surface glycoproteins bind peptide antigens, forming ligands for cytotoxic T and natural killer cell receptors. Under pressure from rapidly evolving viruses, hominoid MHC class I molecules also evolve rapidly, becoming diverse and species-specific. Little is known of the impact of infectious disease epidemics on MHC class I variant distributions in human populations, a context in which the chimpanzee is the superior animal model. Population dynamics of the chimpanzees inhabiting Gombe National Park, Tanzania have been studied for over 50 years. This population is infected with SIVcpz, the precursor of human HIV-1. Because HLA-B is the most polymorphic human MHC class I molecule and correlates strongly with HIV-1 progression, we determined sequences for its ortholog, Patr-B, in 125 Gombe chimpanzees. Eleven Patr-B variants were defined, as were their frequencies in Gombe’s three communities, changes in frequency with time, and effect of SIVcpz infection. The growing populations of the northern and central communities, where SIVcpz is less prevalent, have stable distributions comprising a majority of low-frequency Patr-B variants and a few high-frequency variants. Driving the latter to high frequency has been the fecundity of immigrants to the northern community, whereas in the central community, it has been the fecundity of socially dominant individuals. In the declining population of the southern community, where greater SIVcpz prevalence is associated with mortality and emigration, Patr-B variant distributions have been changing. Enriched in this community are Patr-B variants that engage with natural killer cell receptors. Elevated among SIVcpz-infected chimpanzees, the Patr-B*06:03 variant has striking structural and functional similarities to HLA-B*57, the human allotype most strongly associated with delayed HIV-1 progression. Like HLA-B*57, Patr-B*06:03 correlates with reduced viral load, as assessed by detection of SIVcpz RNA in feces.     

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.     

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.