Within-group cannibalism by adult male chimpanzees

In the Mahale Mountains National Park, Tanzania, a young adult male chimpanzee was observed to feed on a 3-month-old male infant of the same unit-group. Four other adult males and an adult female shared the carcass. The mother of the victim had immigrated from a neighboring unit-group four years previously. Circumstantial evidence strongly suggests that the first-observed cannibal male also killed the infant. The adult male and the mother of the victim had been familiar socially and sexually with each other since the female immigrated. Since the mother of the victim had usually been ranging in the peripheral part of the unit-group's range, i.e., the overlapping area of the two unit-group's ranges during pregnancy and soon after birth, the infanticidal male might have had reason to suspect the paternity of her infant. Four such cases of within-group cannibalism by adult males suggest that the female range and association pattern before and after parturition are key factors allowing an infant to survive. The possibility of male-biased infanticide is also discussed.     

Acoustic variation of pant hoot calls by male chimpanzees: a playback experiment

Pant hoots, a type of long-distance calls of chimpanzees (Pan troglodytes), were played back to two male chimpanzees in a group of seven captive individuals to determine if chimpanzees would modify those vocalizations in response to strange males. Subjects emitted pant hoots with higher rates of delivery, shorter duration of buildup, and lower minimum fundamental frequency of climax when they were presented with pant hoots of strangers than when they produced the calls spontaneously. Considering the direction of acoustical change, we concluded that the rate of delivery, duration of buildup, and minimum frequency of climax might be associated with the underlying emotional states of the callers rather than call matching. Individual difference between two subject males was significant in minimum frequency and duration of climax and in average frequency of call, which appears to reflect differences of the caller's age and social status. These results suggest that different acoustic variables relate to within- and interindividual differences of these vocalizations. Received: March 7, 2000 / Accepted: May 8, 2000     

Demographic influences on the behavior of chimpanzees

Recent research has revealed substantial diversity in the behavior of wild chimpanzees. Understanding the sources of this variation has become a central focus of investigation. While genetic, ecological, and cultural factors are often invoked to explain behavioral variation in chimpanzees, the demographic context is sometimes overlooked as a contributing factor. Observations of chimpanzees at Ngogo, Kibale National Park, Uganda, reveal that the size and structure of the unit group or community can both facilitate and constrain the manifestation of behavior. With approximately 150 individuals, the Ngogo community is much larger than others that have been studied in the wild. We have taken advantage of the unusual demographic structure of this community to document new and intriguing patterns of chimpanzee behavior with respect to hunting, territoriality, and male social relationships. Chimpanzees at Ngogo hunt often and with a considerable degree of success. In addition, male chimpanzees there frequently patrol the boundary of their territory and engage in repeated bouts of lethal intergroup aggression. By forming two distinct subgroups, male chimpanzees at Ngogo also develop social bonds above the level of dyadic pairs. While the sheer number of chimpanzees contributes to differences in hunting, patrolling, mating, and subgrouping at Ngogo, the demographic situation may also constrain behavioral interactions. At Ngogo, male chimpanzees who are closely related genetically through the maternal line do not appear to affiliate or cooperate with each other. Demographic constraints may be responsible for this finding. In this paper, I use these examples to illustrate how the demographic context affects the possible range of behavioral options open to individuals and ultimately contributes to the explanation of behavioral diversity in chimpanzees.     

Comparison of behavioral sequence of copulation between chimpanzees and bonobos

We compared sex differences in behaviors leading to copulation of chimpanzees (Pan troglodytes) in the Kalinzu Forest, Uganda with those of bonobos (Pan paniscus) at Wamba, D.R. Congo, using the same definition. Female chimpanzees were more likely to initiate copulation than female bonobos. While most of copulations (96%) were initiated by males in bonobos, among chimpanzees only 63% of copulations were initiated by males. Female bonobos initiated an interaction leading to copulation when males approached them within a short distance. On the other hand, both male and female chimpanzees initiated behavior at a longer distance. Higher proceptivity and a higher copulation rate during the maximal swelling period of female chimpanzees might suggest that they gain greater benefits from a high frequency of copulations than do female bonobos.     

Ant fishing by wild chimpanzees is not lateralised

Right-dominant handedness is unique and universal in Homo sapiens, suggesting that it is a highly derived trait. Our nearest living relations, chimpanzees, show lateralised hand preference when using tools, but not when otherwise manipulating objects. We report the first contrary data, that is, non-lateralised tool-use, for ant fishing as done in the Mahale Mountains of Tanzania. Unlike nut cracking, termite fishing, and fruit pounding, as seen elsewhere, in which most individuals are either significantly or wholly left- or right-biassed, ant fishers are mostly ambilateral. The clue to this exception lies in arboreality; all other patterns of chimpanzee elementary technology are done on the ground. Arboreal tool use usually requires not only that one hand be used to hold the tool, but also that the other hand gives postural support. When the supporting hand is fatigued, then it must be relieved by the other. Terrestrial tool use entails no such trading off. To test the hypothesis, we compared frequency of hand changing with the incidence of major hand support, and found them to be significantly positively correlated. The evolutionary transition from arboreality to terrestriality may have been a key enabler for the origins of human laterality.     

New observations on the tool-behavior of chimpanzees from Mt. Assirik (Senegal,West Africa)

The tool-behavior of chimpanzees were studied at the Mt. Assirik, in the Parc National du Niokolo-Koba, Senegal from December 1982 to June 1983 and from February 1985 to January 1986. Five leaf-stalks to obtain termites ofMacrotermes subhyalinus species and four sticks to obtain honey (this is the first report on the use of tools to obtain honey by wild chimpanzees in far western Africa) were found; we also report the first evidence of tools probably used as hammers to break open hard-shelled fruits ofAdansonia digitata. We conclude that Mt. Assirik chimpanzees provide evidence of a certain cultural behavior related to the use of stones.     

Spatial aspects of spontaneous object grouping by young chimpanzees(Pan troglodytes)

I report spontaneous spatial object grouping in five chimpanzees (Pan troglodytes)ranging from 1 to 4 years of age. I recorded subjects' spontaneous interactions with groups of objects, noting the spatial relations in the groupings and the constructive processes that the subjects adopted. Though one subject developed vertical stacks, none of them realized horizontal alignments or spatial correspondences between groups. All subjects showed consistent trends in their constructive processes toward manipulating objects in relation to the body: they increasingly manipulated objects globally, that is to say, they moved or held objects together with the same part of the body. They also increasingly placed objects on the body or in correspondence to their symmetrical body parts. The increasing importance assigned by chimpanzees to body- object relations over object- object relations contrasts with human developmental trends in the domain of manipulative space.     

Hierarchy and social status in Budongo chimpanzees

The status hierarchy is fundamental in the lives of male chimpanzees. This study describes the dominance interactions and social status among adult male chimpanzees of the Sonso community in the Budongo Forest Reserve, Uganda, during the period that they were first studied (1994 and 1995). Social dominance is typically measured using the behaviour of either the subordinate or the dominant individual, but a relationship is dependent on the behaviour of both parties and this study explicitly used both subordinate and dominant behaviours to investigate the status hierarchy. Among adult males of the Sonso community, agonistic interactions occurred at a low rate and pant-grunts were rare, but males could be ranked into separate hierarchies of agonistic dominance and pant-grunting (labelled respect) using ratios of behaviour performed/behaviour received. These hierarchies were combined to form a single hierarchy of social status that divided the males among five distinct status levels. The highest status level was held by an alliance between two males who replaced the previous alpha male during the first part of the study. Neither male in this alliance partnership pant-grunted to the other, although the reason for cooperative behaviour was unclear. Although the nominally beta male was treated as such by other adult males, he achieved surprisingly little mating success. Budongo Forest chimpanzees do not warrant the sometimes-expressed view that they are non-aggressive and peaceable and the broad pattern of their status interactions matches with that seen in other chimpanzee populations.     

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.     

What chimpanzees (Pan troglodytes) learn in a cooperative task

To examine the development of cooperation in a captive group of chimpanzees (Pan troglodytes), we designed an apparatus which required the simultaneous traction by two animals to get a reward. Two chimpanzees, an adult male and an infant female in a group of six, produced most of the successful responses (pulling on two handles simultaneously). Visual behavior was used to try to determine what chimpanzees learned about the cooperative task. Propositions were made to investigate what kind of learning could be attributed to chimpanzees and were confronted with results. Both subjects learned the link between the presence of fruits on the apparatus and the possibility of getting a fruit. They also learned the importance of the partner at the apparatus to make a successful response. Only the adult male learned to take into account the behavior of the partner at the apparatus before pulling a handle. From a methodological point of view, the glances made by the animals can constitute a useful behavioral indicator of what the subjects learned in a given social situation.     

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.     

Piagetian stage 5 in two infant chimpanzees (Pan troglodytes): The development of permanence of objects and the spatialization of causality

We investigated the level of cognitive development of two chimpanzee infants, both tested at 14 and 19 months of age, within the Piagetian framework of cognitive development. We administered tasks related to the understanding of object-concept—visible displacement tasks-and the operation of physical causality—the support problem-and observed responses similar to those of human infants. Both subjects reached stage 5 object-concept when they were 19 months of age: only at this time, in fact, were chimpanzees able to find the object wherever it was hidden. Stage 4 errors still characterized infants' performance when they were 14 months old. However, only one of the 19-month-old subjects was able to solve the support problem: she ignored the support when the goal object did not rest on it, showing that the understood the necessity of spatial contact between the target and the intermediary object. On the contrary, the other subject was not proficient in such a task because he drew the support even when the reward was placed beside it. At 19 months of age its level of causality still remained characteristic of the fourth stage.     

Environmental factors influencing the seasonality of estrus in chimpanzees

Although the energetics of the estrous cycle in primates is not well understood, evidence suggests that energy and nutrient acquisition influence ovulation and the timing of conception. Energy for estrus has to compete with energy allocated for cellular maintenance, thermoregulation, movement for food, and predation avoidance. While some chimpanzee (Pan troglodytes) populations do not have a seasonal birth period, evidence suggests that there is seasonality in the number of estrous females. Similarly, the onset of postpartum cycles has been reported to be seasonal. We used 33 months of data from the Taï National Park, Côte dIvoire, to examine how the number of estrous females in a given month was influenced by the abundance and distribution of food, diet, rainfall and temperature. In a second analysis, we examined if there was a seasonal effect on first estrous swellings in adolescent females and postpartum adult females. Results demonstrated that the number of females in estrous in a given month was positively related to food abundance and percent foraging time spent eating insects, and negatively related to mean rainfall in the two preceding months and the mean high temperature. The timing of first estrous swellings of postpartum females and prepartum young females was positively related to the food abundance, and negatively related to mean high temperature. These results showed that environmental conditions can seasonally limit the energetically demanding estrus cycle. The presence of estrous females increases gregariousness in chimpanzee communities, and this study identified environmental factors that affect estrus directly and hence social grouping indirectly.     

Wide-ranging chimpanzees at Mt. Assirik,Senegal

A 4-year study of the ecology and ethology of wild chimpanzees (Pan troglodytes verus)was carried out in far western Africa. Contacts with chimpanzees and the locations of their nests were noted to determine which types of habitat were most used and to estimate the density of the population and the size of its home range. The results show that this community has one of the lowest densities and largest home ranges of all populations of chimpanzees studied so far. As such, it may provide a useful model for the reconstruction of hominid evolution in the Plio-Pleistocene.     

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.     

Conflict and post-conflict behavior in a small group of chimpanzees

Chimpanzee research plays a central role in the discussions of conflict negotiation. Reconciliation, or the attraction and affiliation of former opponents following conflict, has been proposed as a central element of conflict negotiation in chimpanzees and various other taxa. In an attempt to expand the database of chimpanzee conflict resolution, conflict and post-conflict behavior were recorded for a small group of socially housed chimpanzees at the Chimpanzee and Human Communication Institute, at Central Washington University. Data were collected over six 6-week periods between 1997 and 2000, for a total of 840 hours of observation, resulting in a substantial post-conflict (PC) and matched control (MC) data set. The data demonstrate this group’s tendencies to maintain visual contact and closer proximity after conflicts. Dyadic corrected conciliatory tendencies ranged between 0 – 37.5% and averaged 17.25% across all dyads. Individual corrected conciliatory tendencies ranged between 5.8 and 32%. The results of this study combined with recent publications on captive and free-ranging chimpanzee post-conflict behavior suggest that variation in post-conflict behavior may be important to our understanding of chimpanzee conflict negotiation, and may also have implications for the design and management of captive chimpanzee enclosures and social groups, respectively.     

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.     

Laterality of hand use pays off in foraging success for wild chimpanzees

The aim of this study was to see if behavioral lateralization in hand use benefits a lateralized organism in nature. We recorded wild chimpanzees (Pan troglodytes schweinfurthii) at Gombe, Tanzania, fishing for termites (Macrotermes spp.), an extractive foraging task using elementary technology. We compared individual apes who were completely lateralized, using only one hand or the other for the task, versus those who were incompletely lateralized, using either hand. Exclusively lateralized individuals were more efficient, that is, gathered more prey per unit effort, but were no different in success or error rate from incompletely lateralized apes. This is the first demonstration of a payoff to laterality of behavioral function in primates in conditions of ecological validity.