This book comes from a conference on ‘Behavioural Diversity in Chimpanzees and Bonobos’, held 11–17 June, 2000 at the monastery of Seeon in southern Bavaria, Germany. Organized by Gottfried Hohmann and Christophe Boesch, and monitored by Linda F. Marchant, the cloistered meeting heard reports from 30 researchers on 13 different populations of these African apes. Instead of publishing proceedings of the conference, we decided to organize a collection of integrated findings on key topics. Thus, the chapters in this book deviate from the contributions to the Seeon conference in several ways. First, most chapters were greatly edited in order to draw direct comparisons across sites and between species. Second, for the same purpose, some authors who gave separate presentations at the meeting agreed to prepare combined chapters. Third, to enlarge the scope of the book, we asked others who were not present at the meeting to contribute.

This book is the result, and it is devoted only to research on wild populations of Pan, a hominoid genus with two sister species, chimpanzee (P. troglodytes) and bonobo (P. paniscus). Although many research facilities offer excellent housing and stimulating social and non-social environments, when compared with field data, the steady flow of resources, reduced fluctuation in health, safety from predators, and constrained movements limit the ecological validity of their findings.

Behavioural diversity is not a new research topic. There is a rich tradition in comparative ethology of examining given behaviours across species (Lorenz 1950; Hinde & Tinbergen 1958; Wickler 1967; Eibl-Eibesfeldt 1975). These studies focused on species-typical behavioural patterns by comparing closely related taxa.

INTRODUCTION

In nature, access to food sources is constrained and, depending on their diet, individuals compete directly or indirectly to meet their nutritional needs. Sometimes, however, food resources can be divided. Division of food has been seen in vertebrates as diverse as the raven (Corvus corax, Heinrich et al. 1995), vampire bat (Desmodus rotundus, Wilkinson 1984), and chimpanzee (Pan troglodytes, Goodall 1968). For mammalian species, reports on food sharing are mostly for primates and, within this order, Pan dominates the other genera.

In chimpanzees, food sharing occurs most often between mother and dependent offspring (McGrew 1975; Nishida & Turner 1996) and involves plant food. Although food sharing between mature individuals sometimes involves plant food (Lanjouw, Chapter 3; Watts & Mitani, Chapter 18), it is more common in the context of hunting and meat consumption. Hunting of mammalian prey has been reported from all sites where chimpanzees have been studied long term: Assirik (Hunt & McGrew, Chapter 2), Budongo (Suzuki 1975), Gombe (Goodall 1968; Stanford 1995), Kahuzi (Basabose & Yamagiwa 1997), Lopé (Tutin & Fernandez 1993), Mahale (Nishida et al. 1979), Ngogo (Mitani & Watts 1999), Kanyawara (Wrangham, personal communication), Ndoki (Kuroda et al. 1996), Taï (Boesch & Boesch 1989), Tongo (Lanjouw, Chapter 3), Sapo (Anderson et al. 1983), and Semliki (Hunt & McGrew, Chapter 2).

Frequency and style of hunting vary both within and across sites, and appears to be affected by forest structure, prey species and group composition (Lenglet 1987; Boesch 1994; Stanford 1998a; Boesch et al., Chapter 16). Accordingly, food sharing is also likely to vary across different sites or populations.

INTRODUCTION

In the last 20 years, chimpanzee (Pan troglodytes) and bonobo (Pan paniscus) research has produced contrasting pictures of these two sister species. Chimpanzee society has been characterized as male dominated and structured by a linear hierarchy amongst males, with more egalitarian relations amongst females. Male dominance rank is often based on alliances with other males and exerted by intense aggression (Riss & Goodall 1977; Goodall 1986; McGrew 1996; Watts 1998). Parous females, except when they are in oestrus, tend to avoid travelling with males in order to prevent aggression and to improve their foraging efficiency (Williams et al., Chapter 14; Wrangham, Chapter 15). Consequently, parties are relatively small and often male biased (Nishida 1979; Wrangham 1986; Wrangham et al. 1992; Boesch & Boesch-Achermann 2000). In comparison, bonobo society is characterized by egalitarian relations between the sexes (Furuichi 1997) and females may collaborate to defend food sources against males (Idani 1991; Parish 1994; Hohmann & Fruth 1996;Vervaecke et al., 2000). Males establish dominance relationships with each other but aggression amongst males and between the sexes is less intense than in chimpanzees, and conflicts are often settled in a non-agonistic way (Furuichi & Ihobe 1994; de Waal 1995). Compared to chimpanzees, bonobo parties are large and biased towards females. Recently, the behavioural contrasts between the two Pan species have been questioned (Stanford 1998) for various reasons. These include scarcity of information from wild bonobos, and the failure to compare data from wild chimpanzees with what is known from studies of captive bonobos. The goal of this chapter is to address these issues by providing new data on the social organization of wild bonobos.

INTRODUCTION

Over decades apes have served as either referential or conceptual models in attempts to reconstruct the path of human evolution (Ghiglieri, 1987; Wrangham, 1987). In the search for behavioral traits shared by all members of the great apes, few have turned out to be conservative, that is, common features seen in all extant hominoids, and by inference present in our common ancestor. Of these shared traits, skilled object manipulation has been of great interest in comparative analyses as a basic criterion for hominization. Tool use and tool production, however, vary tremendously not only among the four species but also within a single species. Thus the trait in common is not tool use itself, but the general ability for environmental problem solving (McGrew, 1992). Nest building is part of this ability. It is probably the most pervasive form of material skill in apes. Whether or not this trait should be considered as tool use is much disputed (Goodall, 1968; Alcock, 1972; Beck, 1980; Galdikas, 1982).

Nest building is called ‘bed building’ by some investigators (Itani, 1979; Hiraiwa-Hasegawa, 1986). It is a daily habit of weaned great apes to build a place in which to rest. The technique employed depends on the site and on the available materials. Orangutans, chimpanzees and bonobos start their arboreal constructions by preparing a foundation of solid sidebranches or forks, bending, breaking and inter-weaving sidebranches crosswise.