P. J. Baldwin

Chimpanzees in a hot, dry and open habitat: Mt. Assirik, Senegal, West Africa

The habitat of the chimpanzees of Mt. Assirik, in the Parc National du Niokolo-Koba, Senegal, is described in terms of rainfall, temperature and vegetation. The results are compared with those collected at five other sites of study elsewhere in Africa. Mt. Assirik is the driest site at which chimpanzees have been studied, in terms of annual rainfall, proportion of dry months, and number of rainy days. Mt. Assirik is also the hottest such site: the coolest mean maximum temperature at Mt. Assirik exceeds the hottest such temperature at any other site. Mt. Assirik is the only site where chimpanzees have been studied in which the majority of vegetation is grassland. Forest consitutes less than 3% of the surface area. In summary, Mt. Assirik presents a truly open savanna habitat and is thus unique amongst sites where chimpanzees have been studied. These results are compared with data from a tropical foraging human society, the !Kung San of southern Africa. The !Kung Sans habitat is drier on most (but not all) criteria, but Mt. Assirik is hotter. The climate and vegetation of Mt. Assirik strikingly resemble those reconstructed for the Plio-Pleistocene in eastern Africa. This suggests that the chimpanzees of Mt. Assirik provide a useful model for inferring the processes of adaptation in early hominids.

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.

Social organization of savanna-dwelling chimpanzees,Pan troglodytes verus, at Mt. Assirik, Senegal

A community of chimpanzees at Mt. Assirik in south-eastern Senegal subsists in a hot, dry and open environment. This wide-ranging, savanna-living group provides an opportunity for comparisons of social organization with other population elsewhere in Africa living in forest and woodland. The group numbered about 28 over the four-year study, and its composition by age and sex was typical. The average size of parties (i.e., temporary sub-groups) did not differ from other populations. However, a high proportion of the group tended to remain together in such parties. The composition of parties resembled that found elsewhere, but some differences emerged between the wet and dry seasons. Larger, mixed parties containing adult males were much more common in open, non-forested habitats than were solitary individuals or parties without adult males. Large parties tended to form for travelling, especially for rapid movement over long distances. Such aspects of social organization seem unlikely to be related to the availability of food in any simple way. Instead, they seem to be adaptations to threat from predators and patchily distributed food, water and nesting sites. This results in occasional bivouacs and mass-migrations from one part of the home-range to another, especially in the dry season.

Comparisons of nests made by different populations of chimpanzees pan troglodytes

Data on the nests built by chimpanzees were collected in Equatorial Guinea and Senegal. A post-hoc comparison was made on six variables common to both sets of data, and where possible, the effects of season and type of habitat were also compared. The only variable which was not found to differ significantly was the minimum distance between nests. More effects both of season and type of habitat were found in Senegal than in Equatorial Guinea. This is attributed to the marked seasonality and more variable vegetation in the former site. It was concluded that all the differences found in nest-building could be explained by environmental factors and although learning seems to be involved, it remains for further investigation to demonstrate how this might give rise to cultural variation in nest-building.

Responses of Wild Chimpanzees to Potential Predators

This paper reports the responses of wild chimpanzees (Pan troglodytes verus) to the presence of potential predators at Mt. Assirik, in the Parc National du Niokolo Koba, Senegal. Many field studies of wild chimpanzees have been made in the last 20 years but only a few reports have appeared on the responses of chimpanzees to potential predators (Gandini and Baldwin 1978, Izawa and Itani 1966, Itani 1979, Kano 1972, van Lawick-Goodall 1968, Nishida 1968, Pierce, unpubl.). The scarcity of such reports is due largely to the absence or rarity of predators large enough to present a threat to chimpanzees, in the majority of study sites. For example, at both Gombe and Kasoje in Tanzania where chimpanzees have been studied for 20 and 15 years respectively, leopards are the only potential predator and they are extremely rare.