Field experiments are a powerful way of investigating the mechanisms of primate behaviour, their adaptive functions, and the cognitive forces responsible for them. They have several major advantages over observational data. First, they can reduce ambiguity about the causal relationship between stimuli and behavioural responses; second, they allow systematic investigations of even rare events; and third, they can test hypotheses more directly by systematically controlling for confounding variables. Although observational data can sometimes achieve the same results, they typically require more complicated statistical procedures and more observation effort. Field experiments can contribute to a range of scientific disciplines, but they have been used most extensively by psychologists interested in the primate mind, behavioural ecologists working on anti-predator behaviour, and anthropologists dealing with proto-human behaviour and primate culture.
In this chapter, we begin with a brief overview of the main observational methods used in primate fieldwork. We then discuss a number of commonly used experimental designs and stimuli, as well as some further techniques with considerable potential for work with wild primates and conclude by drawing attention to common problems and pitfalls.
Field experiments require a profound understanding of the causes and consequences of the behaviours under study, and they should always be the final step in a research programme based on lengthy, detailed and careful behavioural observations. Without such knowledge, there is a considerable danger of data misinterpretation, inadequate experimental design and meaningless findings.