Fifty-day observation of a free-ranging adult male chimpanzee

An adult male chimpanzee living in Gombe National Park, Tanzania, was observed for 50 consecutive days during the 1974 dry season, for a total of 563 h. This individual, Figan, was the alpha male of a community of 42 chimpanzees. The composition and size of temporary associations within the community was influenced largely by the presence of one estrus female and by characteristics of the food resources. Figan's daily time budget varied little for travel and grooming, but there were major changes in time spent feeding tha inactive over the 50 days. Predatory behavior occurred periodically and meat was eaten on five occasions. Agonistic and sexual behaviors are discussed relative to Figan's high social status. A cooperative relationship was maintained between Figan and his older brother.     

A within-group gang attack on a young adult male chimpanzee: Ostracism of an ill-mannered member?

During a long-term study of wild chimpanzees in Tanzania, an unusual gang attack on a young adult male by the alpha male and seven other members of the same unit group (community) was observed and videotaped. Before the gang attack, the victim had not pant-grunted to the alpha male or to other adult males except for the second-ranked male, but had often bullied adult females without apparent reason. The alpha male's violent behavior, therefore, might have been punishment of or revenge against the ill-mannered young chimpanzee. This is the first record of an adult male other than an ex-alpha male becoming the object of ostracism by wild chimpanzees, although the victimized male did manage to return to the group after more than three months, when an ex-alpha male succeeded in reestablishing his former position.     

Social rejection,exclusion, and shunning among the Gombe chimpanzees

From the observations at Gombe over the past 23 years it appears that group punishment of deviant behavior through ostracism, as practiced in human groups, has not yet evolved in a truly sophisticated way in chimpanzee society. However, cases of “social rejection or exclusion” have been observed in three different behavioral contexts. Most frequently, a chimpanzee is the target of hostility as the result of competitive interaction within the community; in such cases, social cohesion counterbalances rejection, typically leading to integration within a relatively stable pattern of dominance and social interaction. The occasional departure of an individual who has been the target of aggression —like the withdrawal of Evered after repeated attacks by Figan and Faban—seems due to persistent hostility by a few males rather than general “ostracism” by the group as a whole. A second form of exclusion concerns outsiders found in the home range of the group: in these cases, hostility is more generalized, particularly in response to the attempt of an adult female with offspring to join the community. Finally, there are the rarely observed instances of shunning a group member whose behavior seems abnormal the social rejection of Pepe and Old Mr. McGregor after they suffered from polio.     

Able-Bodied Wild Chimpanzees Imitate a Motor Procedure Used by a Disabled Individual to Overcome Handicap

Chimpanzee culture has generated intense recent interest, fueled by the technical complexity of chimpanzee tool-using traditions; yet it is seriously doubted whether chimpanzees are able to learn motor procedures by imitation under natural conditions. Here we take advantage of an unusual chimpanzee population as a ‘natural experiment’ to identify evidence for imitative learning of this kind in wild chimpanzees. The Sonso chimpanzee community has suffered from high levels of snare injury and now has several manually disabled members. Adult male Tinka, with near-total paralysis of both hands, compensates inability to scratch his back manually by employing a distinctive technique of holding a growing liana taut while making side-to-side body movements against it. We found that seven able-bodied young chimpanzees also used this ‘liana-scratch’ technique, although they had no need to. The distribution of the liana-scratch technique was statistically associated with individuals'' range overlap with Tinka and the extent of time they spent in parties with him, confirming that the technique is acquired by social learning. The motivation for able-bodied chimpanzees copying his variant is unknown, but the fact that they do is evidence that the imitative learning of motor procedures from others is a natural trait of wild chimpanzees.     

Ape-like endocast of “ape-man” Taung

I have identified and illustrated a spherical “dimple” or “depression” on the Taung endocast as indicating the most likely position of the medial end of the lunate sulcus but have not drawn an actual lunate sulcus on Taung because one is not visible. In a recent paper, R.L. Holloway (Am. J. Phys. Anthropol. 77:27–33, 1988) drew a lunate sulcus on his copy of the Taung endocast, incorrectly attributed this sulcus to me, and used it to obtain a ratio of 0.254 to describe “Falk's” position of the lunate sulcus. My published ratio of 0.242 for Taung (Falk: Am. J. Phys. Anthropol. 67:313–315, 1985a) was not considered, although the focus of Holloway's paper was my assessment of the position of the lunate sulcus. Holloway also excluded published ratios for a chimpanzee in my collection from his statistical analysis but, even so, my published ratio for Taung is still only 1.5 standard deviations from his chimpanzee mean. If my chimpanzee brain is included in the sample, the ratio for Taung is 1.2 standard deviations from the mean. Furthermore, one of Holloway's own chimpanzees (B60–7) has a ratio of 0.241, just 0.001 below my ratio for Taung. There is no sulcus where Holloway has drawn one on Taung, his “F(LS)” is not mine, his 2 mm error is not mine, and the correct ratio for my measurement of Tuang is the one that I published, not the one that Holloway attributes to me. Assessment of Holloway's chimpanzee data supports my claim that the dimple on the Taung endocast is within the chimpanzee range for the medial end of the lunate sulcus.     

Fatal Chimpanzee Attack in Loango National Park,Gabon

In some populations, chimpanzees engage in lethal aggression within and between social units. We report a fatal attack on an adult male chimpanzee at a new research site in Loango National Park, Gabon. We found a fresh corpse of an adult male chimpanzee only a few hundred meters from the research camp, after noting numerous vocalizations and chimpanzee movements the previous evening. Previous contacts with chimpanzees and fresh tracks in the area around the corpse suggest that 2 communities of chimpanzees range where the attack occurred and that members of the neighboring community killed the chimpanzee. To support the conclusion, we conducted genetic analysis for 13 Y-chromosome loci and 9 microsatellite loci of fecal samples from the dead individual, 5 possible attackers, and 2 members of the other community Though we cannot exclude the possibility of an intracommunity killing, the combined observational and genetic evidence suggest an intercommunity attack. The case study adds to the growing evidence that intercommunity killings are a rare but widespread phenomenon among chimpanzees and not an artifact of human provisioning or habituation.     

Invention and modification of a new tool use behavior: ant-fishing in trees by a wild chimpanzee (Pan troglodytes verus) at Bossou, Guinea

Wild chimpanzees are known to have a different repertoire of tool use unique to each community. For example, "ant-dipping" is a tool use behavior known in several chimpanzee communities across Africa targeted at driver ants (Dorylus spp.) on the ground, whereas "ant-fishing," which is aimed at carpenter ants (Camponotus spp.) in trees, has primarily been observed among the chimpanzees of Mahale in Tanzania. Although the evidence for differences between field sites is accumulating, we have little knowledge on how these tool use behaviors appear at each site and on how these are modified over time. This study reports two"ant-fishing" sessions which occurred 2 years apart by a young male chimpanzee at Bossou, Guinea. Ant-fishing had never been observed before in this community over the past 27 years. During the first session, at the age of 5, he employed wands of similar length when ant-fishing in trees to those used for ant-dipping on the ground, which is a customary tool use behavior of this community. Two years later, at the age of 7, his tools for ant-fishing were shorter and more suitable for capturing carpenter ants. This observation is a rare example of innovation in the wild and does provide insights into problem-solving and learning processes in chimpanzees.     

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.     

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.     

Individual copulatory preference and the “strange female effect” in a captive group-living male chimpanzee (Pan troglodytes)

The common chimpanzee has been considered to be a promiscuous species, although transient consort relationships and male possessive behavior have been described byTutin (1975, 1979). A prolific adult male chimpanzee was housed with from four to seven adult female chimpanzees (depending on the females' maternal status) and copulations were recorded from August 7, 1978 until February 16, 1979, during morning feeding periods. Ten females composed the fluctuating available partners. Sixty-four observed copulations involved six females. One female was clearly preferred, including occasions when she was not maximally tumescent (e.g., completely detumescent, pregnant) and other available females were maximally tumescent. The remainder of the observed copulations, with one exception, involved females who had recently been reintroduced into the one-male breeding group. Such copulations took place on and continued temporarily after the day of reintroduction for two females, and after the resumption of menstrual cycling for two females who had been reintroduced while still lactating. Nonpreferred females were impregnated during the period of data collection, even though copulations with them were not observed. These data suggest that the male chimpanzee can form an individual mating preference regardless of the hormonal status of his available partners without lessening his reproductive success with nonpreferred females, but also tends toward maximization of his reproductive success by copulating with novel females.     

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.     

Apples, oranges, and the lunate sulcus

Holloway (1984) used a method of direct tape-arc measurements on chimpanzee brain casts to reject the hypothesis that the lunate sulcus is located in an anterior position in the Taung endocast. However, Holloway neglected to measure the occipital pole-lunate sulcus (OP-LS) arc directly on the Taung endocast as he did on chimpanzee brain casts (a crucial part of his methodology); instead, he determined the relative position of Taung's lunate sulcus on the basis of a calculation that confounds direct measurements and measurements from photographs. When arc OP-LS is measured directly on Taung according to Holloway's methods, the feature that has been identified as the medial end of the lunate sulcus is shown to be located within the range that Holloway determined for chimpanzees. Thus Holloway's methodology and data support rather than refute the claim that the lunate sulcus is located in a pongid-like position in australopithecines.     

Death of a wild chimpanzee community member: possible outcome of intense sexual competition

Our observations strongly support the view that a lethal gang attack occurred against a young adult male within a wild chimpanzee (Pan troglodytes schweinfurthii) community. This is the first report of such an occurrence. At least three adult male chimpanzees are believed to have been involved in the attack. This case is unusual because the attack was fatal, involved directed group aggression within a community, and was not linked to the overthrow of the alpha male. During the period before the attack, the percentage of cycling females in the community was very low (15 males:17 females, a maximum of two regularly cycling). This fact, coupled with the presence of one female in full genital tumescence, may have incited and escalated the violence of the attack. The lethal attack is interpreted as an act of intra-community male sexual competition resulting in the complete exclusion of one male from estrous females.     

Female reproductive strategies, paternity and community structure in wild West African chimpanzees

Although the variability and complexity of chimpanzee behaviour frustrates generalization, it is widely believed that social evolution in this species occurs in the context of the recognizable social group or community. We used a combination of field observations and noninvasive genotyping to study the genetic structure of a habituated community of 55 wild chimpanzees, Pan troglodytes verus, in the Ta? Forest, C?te d'Ivoire. Pedigree relationships in that community show that female mate choice strategies are more variable than previously supposed and that the observed social groups are not the exclusive reproductive units. Genetic evidence based on nuclear microsatellite markers and behavioural obser-vations reveal that females in the Ta? forest actively seek mating partners outside their social unit; noncommunity males accounted for half the paternities over 5 years. This female mating strategy increases male gene flow between communities despite male philopatry, and negates the predicted higher relatedness among community males. Kin selection seems unlikely to explain the frequent cooperation and sharing observed among group males in this population. Similarly, inbreeding avoidance is probably not the sole cause of permanent adolescent female dispersal as a combination of extragroup mating and avoidance of incest with home group males would allow females to avoid inbreeding without the hazards associated with immigration into a new community. Extragroup mating as part of chimpanzee females' reproductive strategy may allow them to choose from a wider variety and number of males, without losing the resources and support provided by their male social group partners. Copyright 1999 The Association for the Study of Animal Behaviour.     

New cases of inter-community infanticide by male chimpanzees at Ngogo,Kibale National Park,Uganda

Infanticide by males has been recorded in four chimpanzee populations, including that in Kibale National Park, Uganda. Some infanticidal attacks occur during inter-community aggression. The sexual selection hypothesis does not easily explain these attacks because they may not directly increase male mating opportunities. However, females in the attackers’ community may benefit by expanding their foraging ranges and thereby improving their reproductive success; thus infanticide may increase male reproductive success indirectly. We report two new cases of infanticide by male chimpanzees at Ngogo, Kibale National Park. Like two previous cases, these occurred during a boundary patrol and were almost certainly between-community infanticides. The patrolling males attacked despite the proximity of males from the victims’ presumed community. This probably explains why, unlike the earlier cases, they did not completely cannibalize their victims. Such attacks seem to be relatively common at Ngogo and infanticide may be an important source of infant mortality in neighboring communities. Our observations cannot resolve questions about the sexual selection hypothesis. However, they are consistent with the range expansion hypothesis: the infanticides occurred during a period of frequent encounters between communities associated with a mast fruiting event, and Ngogo community members greatly increased their use of areas near the attack site during another mast fruiting event one year later. Our observations contribute to growing evidence that lethal intergroup aggression is a common characteristic of wild chimpanzee populations.     

Dominance rank and fecal testosterone levels in adult male chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda

In an attempt to describe hormone-behavior interactions in a sample of wild male chimpanzees, we quantified testosterone in 67 fecal samples obtained from 22 adult male chimpanzees at Ngogo, Kibale National Park, Uganda. A mixed-model methodology that controlled for age-class identified a significant positive association between testosterone levels and dominance rank. The results are consistent with those reported from a separate, smaller chimpanzee community in the same population in a study that analyzed testosterone levels in urine [Muller & Wrangham, 2004]. As in that earlier study, our results held during a period of social stability, which is not consistent with predictions of the "challenge hypothesis." We concur with Muller and Wrangham [2004] that the challenge hypothesis requires modification to explain the chimpanzee data, because fission-fusion sociality in chimpanzees makes challenges unpredictable. We also discuss the utility of fecal samples and a mixed-model statistical method for behavioral endocrinology studies.     

Intracommunity Coalitionary Killing of an Adult Male Chimpanzee at Ngogo,Kibale National Park,Uganda

Intercommunity coalitionary killing of adult and adolescent males has been documented in two chimpanzee communities in the wild, and it was strongly suspected in a third. It may increase survivorship for the attackers, their mates, and their offspring by reducing the combined strength of hostile neighbors and/or by increasing territory size and food availability, and it may help the attackers to attract mates. Lethal coalitionary attacks by males on other male members of their own communities would not provide these benefits and are not expected, given the importance of cooperation among male community members in contests for dominance rank and in both defense and offense against neighboring males. Nevertheless, intracommunity coalitionary killings associated with struggles for alpha rank occur in the wild and in captivity, and observers have seen serious gang attacks on maturing adolescent and young adult males at Mahale and Budongo: the victim in the Budongo case was killed (Fawcett and Muhumuza, 2000). I describe a lethal attack on a young adult male by a large coalition of males from his community at Ngogo, Kibale National Park, Uganda. The Ngogo community is the largest known for chimpanzees and has an unusually large number of males. The attack was not related to a struggle for alpha rank: the victim was low-ranking and the community had a well-established alpha at the time. However, the victim had risen substantially in the male hierarchy over the past few years and might have appeared threatening to many higher-ranking males. Simultaneously, he associated relatively little with most other adult males, had relatively few grooming partners and was not well integrated into the male grooming network, and had no influential allies. The combination of these social factors with the unusual demographic circumstances – which presumably meant that mating competition was relatively high and the cost of losing one male relatively low – might have triggered the attack.     

ORIGINAL ARTICLE: Tetraparesis resembling acute transverse myelitis in a captive chimpanzee (Pan troglodytes): long‐term care and recovery

Background A 24‐year‐old, male chimpanzee (Pan troglodytes) developed acute tetraparesis. Magnetic resonance imaging showed a diffuse T2‐weighted hyperintensive lesion, indicating inflammation at the C1–2 level. All infective, autoimmune, and vascular investigations were unremarkable. Results and Conclusions The chimpanzee’s condition most resembled acute transverse myelitis (ATM) in humans. The chimpanzee was in severe incapacitated neurological condition with bedridden status and required 24‐hour attention for 2 months followed by special care for over a year. Initially, corticosteroid therapy was performed, and his neurological symptoms improved to some extent; however, the general condition of the chimpanzee deteriorated in the first 6 months after onset. Pressure ulcers had developed at various areas on the animal’s body, as the bedridden status was protracted. Supportive therapy was continued, and the general condition, appetite, mobility, and pressure ulcers have slowly but synergistically recovered over the course of 2 years.     

Technical note: Chromosomal and mtDNA analysis of Oliver

Oliver is an African ape whose species identity has been debated in the popular media and by various scientists since the early 1970s. Although decisive morphological data has never been adduced on Oliver, many reports indicated that Oliver was morphologically unusual for a chimpanzee, particularly in his habitual bipedal posture. In addition, his diploid chromosome number was reported to be inconsistent with either human or chimpanzee, but instead intermediate between those species. We performed standard chromosomal studies which demonstrated that Oliver had the diploid number expected for a chimpanzee (2N = 48) and that the banding patterns of his chromosomes were typical for a chimpanzee and different from both humans and bonobos. We also sequenced a 312 bp region of his mitochondrial DNA D-loop region. Results indicated a high sequence homology to the Central African variety of chimpanzee, Pan troglodytes troglodytes. The highest percent homology was observed with a previously characterized specimen from Gabon, strongly suggesting that Oliver originated from this region. Am J Phys Anthropol 105:395–403, 1998. © 1998 Wiley-Liss, Inc.     

T-strain mycoplasma in the chimpanzee.

Specimens from 4 chimpanzees were cultured for T-strain mycoplasma and Mycoplasma hominis. T-strain mycoplasmas were recovered from the genital tract and throat of a male and the genital tract of his female cagemate; neither had clinical evidence of infection. Two other male chimpanzees were culturally negative for T-strain mycoplasmas. M hominis was not isolated from any of the animals. The chimpanzee may serve as a suitable experimental model for studying the role of T-strain mycoplasmas in human urethritis and reproductive failure.