Cranial capacity estimations of the FrankfurtPan troglodytes verus collection

Cranial capacity measurements of 18 individuals (9 ♂, 9 ♀) of a total collection of 277Pan troglodytes verus skulls were taken using four different methods:- two conventional filling methods and two mathematical methods. The two mathematical analyses normally used in hominids, were for the first time specifically modified forPan. The results probably present a more accurate estimation of total cranial capacity inPan and specifically inPan troglodytes verus (352 cm³) than previously available. Sexual differences related to this trait were also measured. Regardles of the methods used,Pan troglodytes verus seems to manifest the smallest cranial capacity of all subspecies ofPan.     

Heterochrony and sexual dimorphism in the skull of the Liberian chimpanzee (Pan troglodytes verus)

Allometric methods and theory derived from principles of relative growth provide new and powerful approaches to an understanding of the nature and development of sexual dimorphism among living primates. The Frankfurt collection of Liberian chimpanzee skulls and mandibles provides a large skeletal sample from a single natural population of wild shot animals, including individuals of all ages and both sexes, and allows investigation of allometric and heterochronic patterns of sexual dimorphism. Univariate, bivariate, and multivariate analyses are utilized in this study in order to ascertain the ontogenetic nature of male-female differences in the skull of the Liberian chimpanzee. The results of univariate and multivariate analyses indicate that, while overall levels of sexual dimorphism in the chimpanzee skull are small, the greatest differences are in dimensions of the viscerocranium, while neurocranial dimensions and orbital size tend to be less dimorphic. Bivariate regressions of 21 cranial variables against basicranial length document positive allometry in many facial and mandibular dimensions, and isometry or negative allometry for most neurocranial dimensions. The data confirm previous work in chimpanzees and other anthropoid primates suggesting that males and females are “ontogenetically scaled” in most cranial traits. That is, males and females share the same cranial growth trajectories, although ending up at different points. Both rate and time hypermorphosis are suggested as underlying causes of ontogenetic scaling in the Liberian chimpanzee.     

Diet of wild chimpanzees (Pan troglodytes verus) at Mt. Assirik,Senegal: I. Composition

The composition of the diet of a savanna-living population of wild chimpanzees (Pan troglodytes verus) at Mt. Assirik in Senegal is presented. The study site had a prolonged dry season, high temperatures, and vegetation dominated by grasses. Data came from direct observation, fecal specimens, and feeding traces; thus, strict criteria for acceptance of the indirect data were specified. Composition of diet was given in terms of species and family of prey, parts eaten, life-form, type of habitat, and criteria for inclusion. Forty-three species of plants with 60 parts were eaten; mostly fruits, from trees, in woodland. Nine species of animal prey were eaten, mostly social insects. An additional 41 species of plants with 53 parts were classed as likely to be eaten by chimpanzees, mostly on the grounds of their being eaten by sympatric anthropoids. Overall, the diet of the apes at Mt. Assirik resembles that of this species elsewhere in Africa, but the size of the dietary repertoire seems small and the proportion of low-quality foodstuffs high. The latter are mostly time-consuming to collect or tedious to obtain or process, and include underground storage organs.     

Evidence of cave use by savanna chimpanzees (<Emphasis Type="Italic">Pan troglodytes verus</Emphasis>) at Fongoli,Senegal: implications for thermoregulatory behavior

Much attention has been paid to how humans both adapt and acclimate to heat stress, primarily due to the relevance of these issues to hominid evolution in open Plio-Pleistocene environments. However, little is known about the responses of human’s closest living relative, the chimpanzee (Pan troglodytes), to similar environmental stressors. In southeastern Senegal, one of the hottest and driest habitats that chimpanzees (P. t. verus) live in today, apes rely on behavioral mechanisms of dealing with thermal stress. Chimpanzees’ use of caves was based primarily on indirect evidence (feeding traces, feces, and hairs) gathered from one cave from January to December 2004, but data from observational records collected from May 2001 through March 2006 supplement these data. The hypothesis that chimpanzees’ use of caves is a response to heat was tested by collecting data on temperatures within the largest cave and in different habitats used by chimpanzees, such as gallery forest and woodland. Results indicate that chimpanzees primarily use caves as shelters during the hottest times of year and that caves are consistently and significantly cooler than open habitats. Insight into the way that chimpanzees in Senegal cope with extreme temperatures may help us to better understand the behavior of early hominids in such an environment.     

Social behavior and genital swelling in pregnant chimpanzees (Pan troglodytes)

Previous reports of increased sexual activity associated with genital swelling during chimpanzee pregnancy have suggested that the tumescent pregnant female may be regarded as a regularly cycling estrous female. Analysis of additional data from seven pregnant and eight cycling females, however, indicated that tumescent pregnant females differed from cycling females in some social interactions with males. As in earlier reports, pregnant females were more receptive to male-initiated copulatory bouts. In addition, pregnant females initiated grooming bouts with males much less frequently than did cycling females, and males spent less time grooming and less frequently inspected the genitals of pregnant than cycling cagemates. This tendency to decrease social interaction during pregnancy is consistent with field reports that pregnant chimpanzees prefer the company of their offspring and other noncycling females. In addition, the genital swelling patterns of 40 chimpanzee pregnancies were analyzed. Length of gestation averaged 231.5 days. Although a high degree of individual variation existed, females were swollen an average of 41% of the days observed, yet reached maximum swelling only 8.7% of the time. Genital swelling was less frequent during the third trimester, averaging 50.5, 47.9, and 22.6% tumescent days in each trimester. Young pregnant females showed maximum swelling more often than did older females. This finding is discussed with respect to field reports of intercommunity transfer of young, tumescent female chimpanzees.     

Nasal region polymorphism frequencies in the FrankfurtPan troglodytes verus collection

The results of a morphometric study on the mid-facial region in a collection of 278Pan troglodytes verus skulls are reported. Upwardly divergent nasal bones were found in 35 of the 124 specimens (28.2%) in which this feature could be analyzed. Appreciable separation (1 cm. or more) between nasion and glabella characterized 13 of the 154 skulls (8.4%) in which both these osteometric points could be observed. These findings document the wide ranges of variation that are normally to be found in modest-sized population samples of hominoid primates, and point to the inherent unreliability of cladistic analyses based on the hypothesis that hominoid primate taxa are monomorphic for these character states in the nasal region.     

Social influences on ranging patterns among chimpanzees (Pan troglodytes verus) in the Tai National Park, Cote d'Ivoire

Group size is expected to be an important factor to predicthome-range (HR) size in social animals. In chimpanzees adultmales play an important role in defending the HR against neighbors,and therefore it has been suggested that HR size depends onthe number of adult males. In this long-term study on wild WestAfrican chimpanzees, we analyzed the relative importance ofcommunity size and composition on ranging patterns over a 10-yearperiod, using multivariate statistics. Because community sizedecreased from 51 individuals with 6 adult males in 1992 to22 individuals with only 1 adult male in 2001, we expected adecrease in HR size, which should be better predicted by thenumber of males than by community size. We further investigatedthe effect of fruit availability on monthly HRs over a 4-yearperiod. As predicted, HR size decreased during the first 7 yearsof our study but increased during the last 3 years. Overall,the number of adult males was the best predictor of HR size,whereas fruit availability did not correlate with HR size. HRuse remained stable over the entire study period, with a constantproportion of about 35% of the HR used as core area. High HRand core-area overlap values between different years indicatedstrong site-fidelity. Although the number of males within thecommunity explained the decrease in HR size, the recent increasein size remains unexplained. This finding suggests that otherfactors such as relative fighting power of males affect HR size.     

Imaginary Play in chimpanzees (Pan troglodytes)

Imaginary Play was studied in a group of five signing chimpanzees and it was found that chimpanzees engage in imaginary play similar to that found in human children. Fifteen hours of remote videotapes were analyzed for instances of imaginary play. Behaviors were defined as imaginary play by meeting a predetermined criteria which allowed them to be classified into one of six different categories of imaginary play. Six instances of imaginary play were found and these were classified into the two categories of Animation and Substitution. Observations of imaginary play in other research with chimpanzees were discussed.     

Comparing infant and juvenile behavior in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): a preliminary study

The dichotomy between the two Pan species, the bonobo (Pan paniscus) and chimpanzee (Pan troglodytes) has been strongly emphasized until very recently. Given that most studies were primarily based on adult individuals, we shifted the “continuity versus discontinuity” discussion to the infant and juvenile stage. Our aim was to test quantitatively, some conflicting statements made in literature considering species differences between immature bonobos and chimpanzees. On one hand it is suggested that infant bonobos show retardation in motor and social development when compared with chimpanzees. Additionally it is expected that the weaning process is more traumatic to chimpanzee than bonobo infants. But on the other hand the development of behaviors is expected to be very similar in both species. We observed eight mother–infant pairs of each species in several European zoos. Our preliminary research partially confirms that immature chimpanzees seem spatially more independent, spending more time at a larger distance from their mother than immature bonobos. However, the other data do not seem to support the hypothesis that bonobo infants show retardation of motor or social development. The development of solitary play, environmental exploration, social play, non-copulatory mounts and aggressive interactions do not differ between the species. Bonobo infants in general even groom other group members more than chimpanzee infants. We also found that older bonobo infants have more nipple contact than same aged chimpanzees and that the weaning process seems to end later for bonobos than for immature chimpanzee. Additionally, although immature bonobos show in general more signs of distress, our data suggest that the weaning period itself is more traumatic for chimpanzees.     

Oil Palm Use by Adjacent Communities of Chimpanzees at Bossou and Nimba Mountains,West Africa

We investigated oil palm (Elaeis guineensis) use for feeding in 3 chimpanzee communities: Bossou and Seringbara in Guinea and Yealé in Côte d'Ivoire. Bossou was used as the benchmark for comparison. Bossou chimpanzees (Pan troglodytes verus) exhibit a wide range of oil palm targeted behaviors. We used direct observations of their two tool use, i.e., nut-cracking and pestle pounding, to establish strict and reliable criteria to ascertain the presence of comparable behaviors at the two adjacent Nimba sites. Based on monthly surveys of oil palms across the three sites, significant differences in patterns of use emerged. Bossou chimpanzees demonstrated the greatest frequency of oil palm use, while Seringbara chimpanzees, 6 km away, failed to exhibit any use and Yealé chimpanzees, 12 km away, showed all uses comparable to Bossou chimpanzees except pestle pounding and mature leaf pith-feeding. We examined the density and distribution of oil palms, tool availability for nut-cracking and pestle pounding, fruit, flower and nut availability, competition with sympatric species for fruit and nuts and the diversity of fruit species in the diet across the 3 sites. We found no clear difference in proximate environmental variables underlying observed variations in oil palm use among the 3 sites, yielding the conclusion that the differences are cultural. Assuming individual interchange between communities and the involvement of social learning in the intracommunity transmission and maintenance of oil palm uses, the result raises interesting questions about diffusion of behavior between neighboring chimpanzee communities.     

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.     

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.     

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.     

The type locality of <Emphasis Type="Italic">Pan troglodytes vellerosus</Emphasis> (Gray, 1862), and implications for the nomenclature of West African chimpanzees

We show that, in 1862, Richard Burton collected the type specimen of Pan troglodytes vellerosus not on Mount Cameroon, as has been generally assumed, but in Gabon. Therefore, P. t. vellerosus is not the correct name for the chimpanzee population of western Cameroon and southern Nigeria, if that population is taxonomically distinct. As First Reviser, we choose the name Pan troglodytes ellioti for this population of chimpanzees, based on Anthropopithecus ellioti named by Matschie [Matschie P (1914) Neue Affen aus Mittelafrika. Sitzungsber Ges Naturforsch Freunde Berlin 1914:323–342] from a specimen in the Humboldt Museum, Berlin, collected in Bascho (=Basho), Cameroon, and given to the museum in 1905.     

Preliminary survey of the distribution and population of chimpanzees in the Republic of Guinea

An investigation of the distribution and population of chimpanzees in the Republic of Guinea was carried out with the help of the Government authorities on the basis of a questionnaire. As a result, at least 20 out of the 36 prefectures in the country were confirmed to be inhabited by chimpanzees, and the estimated total number of animals in the present population amounted to 6,625. This number represented an approximately 50% reduction from the 13,940 estimated by the same informants on the same questionnaire based on assumptions for the past (20–60 years ago). On comparing these data with our observations in some localities, the present number of chimpanzees as estimated from the questionnaire appeared to be overestimated. Among the 16 other prefectures without any reply, at least 7 have chimpanzees according to our own and our colleagues' observations. On our modest estimate, the number of chimpanzees at present could be only about 1,420 for 30 prefectures rather than 6,625 for 20 prefectures. The true population size in the whole country may lie between the two estimates, 1,420–6,625, even including other prefectures with no information. The reduction in population size during the last 20–60 years must be half or even more. The reason for this drastic reduction of the chimpanzee population is thought to be mainly the destruction of its habitat and poaching in some prefectures adjacent to Sierra Leone and Liberia. These findings emphasize that urgent efforts need to be directed towards the conservation of the chimpanzees and their habitat, especially through international cooperative programmes.     

Tool use by wild chimpanzees (Pan troglodytes) to obtain termites (Macrotermes herus) in the Mahale Mountains,Tanzania

Wild chimpanzees (Pan troglodytes) used probes made of vegetation to fish for termites (Macrotermes herus) in the Mahale Mountains of western Tanzania. Data on both the artefacts and behavior associated with their use were recorded over a 5-month period. The chimpanzees of one unit group, B Group, were seen four times to use the tools to extract the insects from their mounds. A sample of 290 tools was collected and analyzed in terms of age, seasonality, length, width, class of raw materials, species, methods of making, extent of use, and damage incurred through use. There were differences across groups in tool use in feeding on termites; some could be related to biotic factors, but others appeared to be cultural differences.     

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.     

Factors Affecting Party Size in Chimpanzees of the Mahale Mountains

We studied factors affecting party size and composition of wild chimpanzees at Mahale (M group) over an 11-month period. Parties with 1–5 individuals were most frequent (37.8%; 153/405 parties); they included 94.7% of all male parties (n = 76) and 81.3% of all female parties (n = 75). The median of monthly values was the standard for analysis. We divided the year into four periods based on the median size of monthly bisexual parties (30.9 individuals; includes both males and females): monthly bisexual party sizes were larger in May–June (period II) and October–January (period IV) and smaller in February–April (period I) and July–September (period III). Only bisexual parties changed in size with period. The number of fruit items (=species) eaten was fewer in periods II and IV when abundance per item appeared to be great. The sizes of bisexual parties, which included cycling females with maximal anogenital swelling, were larger, and their representation (%) in all bisexual parties was greater in periods III and IV. The numbers of both cycling females and cycling females with maximal anogenital swelling were also larger in periods III and IV. The percentage of cycling females with maximal anogenital swelling was greater in periods II and III. The results of this study and those of Nishida (1979) suggest that seasonal variation in party size of Mahale chimpanzees maintains a relatively consistent annual cycle. The factors assumed to affect party sizes are fruit availability and the presence of cycling females with maximal anogenital swelling.