Tool-using and -making behavior in wild chimpanzees at Bossou,Guinea

The behavior of wild chimpanzees at Bossou, Guinea, was studied from November 1976 to May 1977 recognizing each chimpanzee without artificial feeding. During the study period some tool-using and tool-making behavior was observed, as follows: (1) Although water drinking using a “leaf-sponge” was not seen, that using a “leaf-spoon” was observed for taking water from the hollow of a tree. (2) “Termite fishing” was not seen in this group although there were many termite hills in the moving range of the chimpanzees. They dug termites from the hollow of a tree by pounding with a small stick. Similar use of a stick was made for digging up the resin from a tree. (3) “Aimed throwing” was frequently observed in adult males for attacking an observer, and in adolescents and juveniles as mischief against an observer or for their own play. (4) “Nut cracking” with a pair of stones was seen for removing the ovule from palm-seeds. Particular stones were repeatedly used by many chimpanzees for a long period. (5) “Branch hauling” represented difficult work. Patient and inventive manufacture of proper sticks was necessary for capturing branches which they were unable to reach normally. Local variations in the tool-using patterns and manufacturing ability of chimpanzees are discussed.     

Social structure and dynamics of wild chimpanzees at Bossou,Guinea

A small population of wild chimpanzees was studied at Bossou, Guinea, for six months from November 1976 to May 1977. All the chimpanzees except dependent infants were identified without artificial feeding and were observed from within 20 m almost every day. The population size of 21 chimpanzees was little changed from 1967. Although the sex ratio (male/female) of immatures (infants, juveniles, and adolescents) was 0.833 in January 1977, the adult sex ratio was 0.429. More than half of the males must therefore have disappeared. No desertion of males from the Bossou group was confirmed during the study period but two emigrated males from other groups did come to join the Bossou group for a short period. Four out of six mothers had two or three children. From the age discrepancy of brothers/sisters, the mean birth interval from a mother was estimated to be about four years. An elder sister of two infants who had an age-gap of only three years, or perhaps less, disappeared without receiving sufficient care from her mother. Mothers who had infants aged about 1 year or more showed swelling of their sexual skin and were confirmed to mate with males.     

Drinking tools of wild chimpanzees at Bossou

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

Demographic parameters and life history of chimpanzees at Bossou, Guinea

Demographic parameters of wild chimpanzees at Bossou, Guinea, are presented and compared with those of other populations. The population size of Bossou chimpanzees has been stable over the last 26 years, except during two incidents of partial deforestation. The annual birth rate for a female (mean = 0.194, but 0.165 when the infant survived more than 4 years) and interbirth interval are not much different from those of other study sites. The primiparous age of Bossou chimpanzees, however, is far younger (mean = 10.9 years) than for all other known wild chimpanzee populations. The infant and juvenile survival rate is also the highest (female = 0.64, male = 0.52 for the first 8 years). As a result, the lifetime reproductive success of Bossou chimpanzees is estimated to be highest among long-term study sites. The rate of disappearance from Bossou dramatically increases during the adolescent stage, and most young chimpanzees disappear before or around maturation. Probably because the environmental capacity for chimpanzees at Bossou is at its limit, many young independent males, as well as females, have to disperse, though others may die. For chimpanzee alpha males of other populations, mature males may be needed as collaborators to defend resources. In the case of Bossou, however, a lack of adjacent groups, conspecific competitors, predators, and perhaps medium-sized mammals as prey for group hunting may eliminate this need of the alpha male for other males. The reasons why all males of other chimpanzee populations persist in being philopatric for life and maintain kin-related male bonds differing from most mammal species, including humans, are discussed.     

Flexible feeding on cultivated underground storage organs by rainforest-dwelling chimpanzees at Bossou, West Africa

It has been proposed that exploitation of underground storage organs (USOs) played an important role in the evolution of the genus Homo, these items serving as ‘fallback foods’ during periods of low food availability. The use of USOs as food by wild chimpanzees is infrequent and seen mostly in populations inhabiting relatively arid environments, such as the savanna. Here, we specifically test the hypothesis that chimpanzees (Pan troglodytes verus) inhabiting tropical wet forest at Bossou (Republic of Guinea, West Africa) exploit USOs as a fallback food during periods of fruit scarcity. Chimpanzees were never observed feeding on wild USOs, that is, those that were never cultivated, and rarely on other underground plant parts. However, direct observations revealed regular consumption of the USOs of cultivated cassava (Manihot esculenta), a spatially abundant and continuously available plant, although the chimpanzees did not use tools when acquiring and feeding on cassava. In agreement with the fallback foods hypothesis, our results show that chimpanzees exploited cassava USOs more frequently when both wild and cultivated fruits were scarce, and consumption patterns of cassava paralleled those of wild fallback foods. These seasonal extractive USO foraging strategies by chimpanzees can strengthen attempts to construct a clearer picture of the importance of USO feeding in hominoid evolution.     

Age-specific birth rate and lifetime reproductive success of chimpanzees at Bossou,Guinea

Preliminary calculations of the age-specific birth rate for wild female chimpanzees were based on demographic records from a long-term study at Bossou, Republic of Guinea. Primiparous age was 12-14 years. Birth rate for a female reached a peak of 0.333 a year at 20-23 years, and then decreased until menopause at more than 40 years of age. Mean birth rate for a female of more than 12 years was 0.197 a year. Mean interbirth interval was 4.6 years overall, but 5.1 years, if all cases in which the previous infant had died within its first three years were excluded. Infant survival rate for the first four years was 0.727 and that of juveniles (four to seven years) was 0.714; however, that of adolescents (eight to 11 years) was only 0.222. Some adolescents who disappeared from Bossou are thought to have migrated to adjacent habitats. From age-specific birth rate and survival rate, the lifetime reproductive success was calculated as only 0.74 offspring per female. This rose to 2.39 when adolescent survival rate was assumed to be the same as that of juveniles. This must be less than the minimum reproductive success required for continued survival of the population. The recent and continuing degradation of the environment will lead to the extermination of this species from the area in the near future. © 1994 Wiley-Liss, Inc.     

Capturing and toying with hyraxes (Dendrohyrax dorsalis) by wild chimpanzees (Pan troglodytes) at Bossou, Guinea

Chimpanzees (Pan troglodytes verus) were observed capturing and toying with western tree hyraxes (Dendrohyrax dorsalis, Order Hyracoidea) at Bossou, Guinea. An adolescent female carried one hyrax for 15 hr, slept with it in her nest, and groomed it. The captive was not consumed. Nearby adults ignored the hyrax. In another case, two adolescent males timidly inspected a small hyrax. These observations indicate that the chimpanzees at Bossou do not regard the hyrax as a prey animal, supporting the idea that lack of opportunity does not seem to be the only reason that chimpanzees do not consume an individual of a potential prey species.     

A case report of a novel type of stick use by wild chimpanzees

We have found evidence that wild chimpanzees used stout sticks to dig into one end of a decayed fallen trunk from the side and a long stick with a frayed end to dig into or brush its stump, in the Moukalaba Reserve, Gabon. This type of stick use by wild chimpanzees has not been recorded in any habitat. This finding should contribute to future studies and discussions of variations in tool use and cultural processes among wild chimpanzees. Electronic Publication     

Grooming interactions among adult chimpanzees at Bossou,Guinea, with special reference to social structure

Grooming and proximity interactions among chimpanzees at Bossou, Republic of Guinea, were analyzed as an index of friendly and affinitive relationships among adult males, among adult females, and between the sexes. Data from the first (1976–1977) and the third (1982–1983) study period were used. The expected value of their interactions was calculated from the number of adult males and females in the group and also from the observed frequency of combinations of adult males and females in the parties (temporary foraging groups). In the pooled data from the two periods, there was little difference between grooming and proximity (without grooming). The frequency of male-female grooming and proximity interactions was lower than expected, and that of female-female interactions was higher than expected. The frequencies of male-male grooming and proximity were intermediate but fluctuated. Male-male grooming frequency was lower than that recorded in chimpanzees of East Africa. Characteristics of same-sex affinitive interactions, especially between Bossou chimpanzee females, clearly differ from those of East African chimpanzees and are more like those recorded for female-related groups of Japanese macaques (Macaca fuscata).These differences indicate the variability and flexibility of chimpanzee social structure.     

Chimpanzees in Bwindi-Impenetrable National Park, Uganda, use different tools to obtain different types of honey

Evidence of tool use for foraging for honey by chimpanzees in Bwindi-Impenetrable National Park, Uganda, is reported. These are the first records of tool use by chimpanzees in this region of the Albertine Rift. Tools of two types were found at sites of bee activity. Chimpanzees apparently use small stick tools to forage for the honey of a stingless bee [Meliponula bocandei (Trigonidae)] that nests in tree cavities and also in subterranean holes. They use significantly larger, thicker tools to assist in foraging for honey of African honeybees (Apis mellifera).     

A preliminary list of chimpanzees' alimentation at Bossou,Guinea

A preliminary list of all the plant and animal foods for wild chimpanzees at Bossou, south-east of the Republic of Guinea, is presented for comparison with that of other study areas and as the basic data for the further studies. Altogether 205 food items (species × part eaten) from 156 species in 106 genera of plant food are recorded (Table 1). On the other hand little of animal food has been recorded (Table 2). Thus only one species of mammal (tree pangolin) and bird (wood owl) are represented in the diet along with only a few types of other animals. As calculated from number of food items fruits and seeds (nuts) occupy more than half of the diet; and leaves, shoots, and twigs (stems) constitute about one third.     

Nut cracking by wild chimpanzees in Sierra Leone,West Africa

I report an incidence of chimpanzee (Pan troglodytes verus) cracking ofDetarium senegalense (Caesalpiniaceae) nuts on Tiwai Island, Sierra Leone. Similar behavior has been reported from other West African locations, but not from Central or East Africa.     

Socioecological factors of male chimpanzee migration at Bossou, Guinea

For more than 21 years a small semi-isolated group of wild chimpanzees have been studied at Bossou, Guinea, west Africa. All individuals have been identified since the beginning of the study. Remaining rates of infants (0–3 yr) and juveniles (4–7 yr) in the group were 64–80% for both sexes, however, those of adolescents (8–11 yr) dropped drastically, particularly for males (14%). As a result, most natal males as well as females disappeared before fully maturing. Two male visitors and an immigrant were observed in the group. More adult males than females disappeared from Bossou. Group males could be excluded as the genetic father of an offspring born in the group. From these demographic trends it is highly likely that some of these males emigrated rather than succumbed to sickness and death. It seems likely that they left on their own by choice. The reason for male dispersal is hypothesized to be influenced by intra-group male-male competition and the habitat ecology and structure of Bossou. There are no competitive adjacent groups or predators to prevent males from living alone and males can sire offspring out of their natal group.     

Factors affecting party size and composition of chimpanzees (Pan troglodytes verus) Bossou,Guinea

I studied the party sizes of western chimpanzees (Pan troglodytes verus)and factors assumed to affect them at Bossou, Republic of Guinea, West Africa. Party size is negatively correlated with feeding ratio, and larger parties tend to be formed in more dangerous situations (i.e. crossing roads with much traffic). When parties included estrous females, young (i.e., late juvenile and adolescent) males tended to forage with them, independently from their mothers. Lactating females with infants tended to spend more time alone, but the trend was not as apparent as it is in P. t. schweinfurthiat Gombe, Tanzania. These facts suggest that several factors, in addition to food availability, affect party formation, or fission-fusion, of chimpanzees. I also briefly discuss comparatively the pattern of party formation in P. paniscus.     

Infanticide and cannibalism by male chimpanzees at Ngogo, Kibale National Park, Uganda

Researchers have documented infanticide by adult males in four wild chimpanzee populations. Males in three of these have killed infants from outside of their own communities, but most infanticides, including one from Kanyawara, in Kibale National Park, Uganda, took place within communities. Here we report two new cases of infanticide by male chimpanzees at a second Kibale site, Ngogo, where the recently habituated chimpanzee community is the largest yet known. Both infanticides happended during boundary patrols, which occur at a high frequency there. Patrolling males attacked solitary females who were unable to defend their infants successfully. The victims were almost certainly not members of the Ngogo community. Males cannibalized both infants and completely consumed their carcasses. These observations show that infanticide by males is widespread in the Kibale population and that between-community infanticide also happens there. We discuss our observations in the context of the sexual selection hypothesis and other proposed explanations for infanticide by male chimpanzees. The observations support the arguments that infanticide has been an important selective force in chimpanzee social evolution and that females with dependent infants can be at great risk near range boundaries, but why male chimpanzees kill infants is still uncertain.     

Ant dipping and meat eating by wild chimpanzees in the kalinzu forest, uganda

New evidence of ant dipping and meat eating by chimpanzees was recorded in the Kalinzu Forest, Uganda. We found stems and branches at the nests of driver ants,Dorylus molestus, just after chimpanzees had left the spot. Fecal samples also revealed that chimpanzees sometimes ate driver ants. The configuration of stems and branches and the condition of holes at the driver ant's nests suggested that chimpanzees used them as wands to dip for ants. The frequency of ant dipping and length of wands may be more related to culturel rather than ecological factors. Although hunting was not seen, we found chim-panzees eating a blue monkey and a redtail monkey. In both cases, they ate meat and leaves alternatively, and shared meat with each other.