Saving the gorillas (Gorilla g. gorilla) and chimpanzees (Pan t. troglodytes) of the Congo Basin

The forests of the Congo Basin in equatorial Africa are home to significant populations of gorillas and chimpanzees. However, numbers are declining owing to hunting and to alteration of their habitat. Gorillas and chimpanzees are particularly vulnerable for biological reasons: slow reproduction, prolonged developmental periods and complex social behaviour. In addition, their capacity to recover from disturbance is limited and the reinforcement of wild populations with captive-born individuals is rarely an option. Compared with the critically endangered mountain gorillas and the beleaguered chimpanzees in forest fragments in West Africa, there are some reasons for optimism about the future of the Congo Basin apes: levels of threat remain relatively low; and conservation of tropical rainforests has become a priority of the international community. At the same time, knowledge of the ecological needs of wild apes has increased and non-invasive techniques now exist to monitor population health. Sadly, no animals remain truly 'wild', as their survival depends to a greater or lesser extent on management. Protected areas and laws that forbid hunting of vulnerable species are classic tools of management, but broader landscape visions are now emerging that may allow the Congo Basin to avoid the fragile scenario of larger animals persisting only in 'island' parks.

The primate community of the Lopé Reserve, Gabon: diets, responses to fruit scarcity, and effects on biomass

The diets of all diurnal primates (Gorilla g. gorilla, Pan t. troglodytes, Mandrillus sphinx, Colobus satanas, Cercocebus albigena, Cercopithecus nictitans, C. pogonias, C. cephus) in the Lópe Reserve, central Gabon, are described from qualitative and quantitative data collected over 10 years. A total of 397 foods were recorded, of which 91% were from plants. The diet of seven of the eight species were numerically dominated by fruit, the exception being Colobus satanas with a diet dominated by seeds. When proportion of feeding time was examined, fruit remained the dominant food class for six species, while Cercocebus albigena, like the black colobus, spent most time feeding on seeds. The number of foods recorded per species ranged from 46-220, but dietary breadth of the four species that have not been subjects of detailed study was certainly underestimated. Almost half of the foods (46%) were eaten by only one species, and only four (1%) were recorded for all eight species. At Lópe, fruit is scarce for 2-3 months during the annual dry season, and fruit crop failures can prolong this period of scarcity to as many as 8 months in some years. When fruit is scarce, the diets of all the species changed to include more nonfruit foods, but chimpanzees and the three species of guenons maintained a fruit dominated diet. The total biomass of the Lópe primate community is 374 kg/km2, which is low compared to other sites in tropical Africa. Within the Lópe community, biomass correlates negativity with degree of frugivory, suggesting that fruit availability may be critical, but this does not explain the low total biomass compared to other sites. Neither floristic diversity nor the composition of the primate community at Lópe can account for the biomass. While historical events such as climate-induced changes in forrest cover, disease, or impact of human activities cannot be ruled out, we conclude that the most likely explanation of low primate biomass is the occurrence of an ecological "catastrophe" in the fairly recent past from which populations have not yet recovered. We believe that the most likely scenario was climate-mediated disturbance of flowering of important fruit food species. Prolonged fruit scarcity would have caused mortalities and affected the most frugivorous species more severely.

Lowland gorillas and seed dispersal: the importance of nest sites

Lowland gorillas eat the fruit and disperse the seeds of many tree species in the Lopé Reserve, Gabon. This study aimed to show whether deposition of seeds at gorilla ground nest sites conferred any advantage for germination and seedling establishment as compared to the fate of seeds deposited in gorilla dung on trails or under parents. Four tree species were chosen for study, which had a range of fruit types and fruiting patterns but which were all important foods for gorillas. Data showed that gorillas removed significant quantities of seeds from all four species and deposited them in dung at nest sites or on trail. Nest sites were not always favorable for germination, but the most favorable sites permitted the best survival and growth of any of the seedlings, including those deposited in dung on trail or scatter-dispersed under or away from parent canopies. Initial performance in the first few weeks after deposition was not always indicative of long-term survival and growth, so data collection over 1-2 years was absolutely essential. The main factors affecting seedling fate at nest sites appeared to be vegetation cover and desiccation. It is suggested that the nesting habits of gorillas are an additional factor encouraging the successful establishment of seedlings over and above the obvious advantages of large body size, gut capacity, and extended day ranges.

[Ecology and social organization of African tropical forest primates: aid in understanding retrovirus transmission]

The risk of transmission of primate viruses to humans is great because of their genetic proximity. It is now clear that the HIV group of retroviruses came from primates and that the origin of HIV1 is the chimpanzee subspecies of Central Africa, Pan troglodytes troglodytes. Many African primates are natural hosts of retroviruses and details of the natural history of both hosts and viruses are essential to understand the evolution of the latter. Data on the demography, ecology and behaviour of three species of primates (gorillas, chimpanzees and mandrills), studied in the Lopé Reserve in Central Gabon since 1983, are analysed to identify the factors that allow, or favour, disease transmission within each species, between different species and between primates and humans. The comparison of the relative degree of risk suggests that of the three species, chimpanzees are the most susceptible to exposure to infection both from conspecifics and from other species. With respect to humans, the comparative analysis suggests greater exposure to viruses of mandrills and gorillas than to those of chimpanzees. For primates, major risk factors are: large social groups; bites inflicted in fights; social grooming; and predation on mammals. However, given that contacts between social groups of the same species are rare, the spread of a virus through a population will be slow and uncertain. Hunting wild animals is the behaviour most likely to provide transmission routes for primate viruses into human populations because of the high probability of blood-blood contact. Not only the hunters themselves, but also women who prepare bush meat for cooking and people involved in trade of carcasses are at high risk of transmission of pathogens. Hunting of bush meat is increasing in Central Africa due to the economic recession and the spread of logging into the forests of the interior of the region. To counter the significant risk of transmission of known, as well as new, diseases from primates to humans, urgent measures are needed to attack the root causes of commercial hunting which is not only risk to public health but also a serious threat to biodiversity in the region.

Cultures in chimpanzees

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation. Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumulated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans. We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds. The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinctive, a phenomenon characteristic of human cultures but previously unrecognised in non-human species.

Intestinal parasites of sympatric gorillas and chimpanzees in the Lopé Reserve, Gabon

A coprological survey of intestinal parasites of wild chimpanzees (Pan t. troglodytes) and western lowland gorillas (Gorilla g. gorilla) was carried out in the Lopé Reserve in central Gabon. Most samples (69%) were positive but the prevalence of intestinal parasites in the 61 gorilla samples (84%) was higher than in the 66 chimpanzee samples (56%). At least 11 species of parasite were observed: six protozoan, one trematode and at least four nematodes. Six of the species were found in gorillas and chimpanzees but the remainder only occurred in chimpanzees. All but one parasite occurred at low prevalences. Entodiniomorph ciliates, which occurred frequently in both ape species (particularly in gorillas) in the Lopé survey and in all previous coprological surveys of wild apes, may be symbionts involved in cellulose digestion. The dietary and behavioural strategies of wild primates that serve to reduce infection by pathogenic parasites are reviewed.

Foraging profiles of sympatric lowland gorillas and chimpanzees in the Lopé Reserve, Gabon

Comparison of the diets of sympatric gorillas and chimpanzees allows an analysis of niche separation between these two closely related species. Qualitatively, their diets are similar, being dominated by an equally diverse array of fruit species complemented with vegetative plant parts, seeds and insects. Gorillas eat more vegetative plant parts than do chimpanzees, but niche separation is most obvious in periods of fruit scarcity when the two species show different strategies that reduce competition for food. Their abilities to overcome mechanical and physical plant defences appear to differ, as gorillas are able to subsist entirely on abundant vegetative foods. Chimpanzees show social adjustment, foraging alone or in small groups, to reduce intra-specific competition for scarce fruit resources. Thus it seems that subtle physiological differences have far-reaching repercussions, defining potential evolutionary pathways for social organization and allowing sufficient niche separation between species.

Possible osteomyelitis of skull causes death of a wild lowland gorilla in the Lopé Reserve, Gabon

The remains of a juvenile gorilla, apparently dead for 3-4 days, were found in the Lopé Reserve, Gabon. The skull was recovered and showed a chronic lesion involving the insertion of the masseter muscle, consistent with chronic osteomyelitis.

Reproductive behaviour of wild chimpanzees in the Gombe National Park, Tanzania

(1) The reproductive behaviour of chimpanzees in the Gombe National Park, Tanzania, was studied for 16 months and additional information came from 19 years of demographic data collected by Dr Jane Goodall and members of the Gombe Stream Research Centre. (2) The mating system of the Gombe chimpanzees comprises 3 mating patterns: (a) opportunistic, non-competitive mating, when an oestrous female may be mated by all the males in the group; (b) possessiveness, when a male forms a special short-term relationship with an oestrous female and may prevent lower ranking males from copulating with her; and (c) consortships, when a male and a female leave the group and remain alone, actively avoiding other chimpanzees. While males took the initiative in possessive behaviour and consortships, females had to co-operate for a successful relationship to develop. (3) Data from 14 conceptions indicated that the majority of females (9) became pregnant while participating in the restrictive mating patterns, possessiveness and consorting. Adult males showed differential frequencies of involvement in the restrictive mating patterns. The following male characteristics showed significant, positive correlations with participation in the restrictive patterns: (a) the amount of time spent in the same group as oestrous females, (b) the proportion of that time spent grooming oestrous females, and (c) the frequency with which males shared food with females. Dominance ranks of the adult males showed no consistent correlation with involvement in the restrictive patterns, but it was clear that the most dominant male did gain an advantage. He was the only male able to monopolize oestrous females by showing possessiveness. (4) Developmental and demographic data from observations for 19 years show that female chimpanzees have a very limited reproductive potential. Females reached menarche at about 11 years of age but this was followed by a period of adolescent sterility of median length 26 months. Each birth, if the infant survived, was followed by a long period of lactational amenorrhoea of median duration 42 months. The mean inter-birth interval of the Gombe chimpanzees was 5 years 8 months. Thus, the theoretical lifetime reproductive potential of females is 5-6 offspring who survive to weaning. Data on achieved reproductive success showed that females had a median of 3 births in their lifetime, with only 2 offspring surviving to reproductive age.

The intestinal parasites of a community of feral chimpanzees, Pan troglodytes schweinfurthii

Fecal specimens from 32 champanzees living in Gombe National Park, Tanzania, were examined. Six species of helminths and 2 species of ciliates were found: Probstmayris gombensis File (in press), Strongyloides fuelleborni von Linstow 1905, Necator sp., Oesophagostomum sp., Abbreviata caucasica von Linstow 1902, Trichuris sp., Troglodytella abrassarti Brumpt and Joyeux 1921, and an unidentified ciliate. None of the parasitic infections were heavy. This is the first such survey of the chimpanzee in its natural habitat.

Tool use in a group of captive chimpanzees I. Escape

A group of 4 female and 3 male adolescent wild-born chimpanzees was observed for 7 months in an outdoor enclosure. Use of tools aimed at escaping from this enclosure is decribed, the two main techniques being the use of poles as ladders and sticks as pitons.

Chimpanzee copulatory behaviour

Observations were made of a group of adolescent chimpanzees (Pan troglodytes) living in one-acre field enclosure. In 1,200 h of observation, we observed 341 copulations involving six individuals. 34 elements of copulatory behaviour were described and recorded, including facial expressions, vocalisations, gestures, postures and locomotion. Frequencies, combinations and sequences of the elements were extracted in analysis. The results emphasise individual differences and the rapid ontogeny of copulatory behaviour elements.