Behavioural ecology of chimpanzees in Gombe National Park, Tanzania

Abstract

Chapter I The aims of this study are to understand certain relationships between the behaviour and ecology of chimpanzees. By studying one population over time many complicating factors are eliminated. The behaviour of females changes according to their reproductive state: in order to focus attention on behavioural responses to environmental change, only adult males, in two communities, were selected as target individuals. Chapter 2 The study population and its habitat ~ described and recording methods are outlined and discussed. Chapter 3 The aim in describing feeding behaviour is to identify and explain seasonal changes. Chimpanzees are found to have an intimate knowledge of their environment and its food sources; the data do not support previous suggestions that the function of dispersal and aggregation to locate foods. Evidence from a series of dependent measures indicated that more food was available in the second of two dry season periods of observation. At this time parties were larger. Apparently when food is scarce the behaviour of individuals is directed to maximising feeding efficiency; when food is abundant males may forego maximisation of feeding efficiency for the sake of increased reproductive effort. Chapter 4 All observations of chimpanzees eating animals in Gombe National Park are listed. The factors affecting predation by chimpanzees are considered, and it is concluded that opportunity is the most important III · IV determinant of predatory interest. The frequency of predation on mammals is calculated, and prey species are found to suffer mortality rates comparable to the prey of true carnivores. Food transfer during meat- eating is considered to be the outcome of competition for an item which is not easily divisible and can be carried. Chapter 5 Data are presented on the ranging behaviour of individuals over one day, four days and one year, and on the directions from which individuals entered the artificial feeding area. It is found that despite considerable overlap individuals use different core areas. Although males may be regarded as forming distinct communities, some females do not conform to male community'rules': for instance they associate peacefully with males of more than one community. A new model of chimpanzee dispersion is proposed. Factors affecting travel patterns are discussed. Larger ranges occurred when more food was available, and are suggested to represent increased reproductive effort. Chapter 6 Some chimpanzees were g~ven bananas at an artificial feeding area: the possible influence of artificial feeding is discussed. Though its consequences may be widespread they were reduced ~n this study by appropriate methods of observation and analysis. The form of chimpanzee social structure is suggested to depend on the feeding strategies of mothers. This principle is applied to other apes and species with similar social structures.

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