silvia rocha

ABSTRACT The present work was carried out at the Mona Foundation Rescue Centre (Spain). This sanctuary holds two semi-free ranging rehabilitant groups of socially functional chimpanzees, known as “family group” and “bachelor group”. The study aimed to assess the effect of several stimuli on the behaviour of the chimpanzees and to determine the most adequate stimuli to elicit positive and negative emotional behaviour responses. Part of the materials used in these experiments had been pre-tested in similar experiments with these two groups of chimpanzees, as part of a preliminary study to induce and study surprise and respective reactions. With a few exceptions, objects were familiar treats or toys. Sessions began with subject’s morning release into outdoor space. Field experimental conditions were pre-prepared so that chimpanzees found the stimuli apparatus shortly afterwards, as they roamed about the landscape. The plan for the emotional induction field experiments consisted in 3 experimental conditions (neutral/positive/negative) and for each apparatus there were 4 variations of stimuli, so that each of the 4 sessions per condition (replicas) that each group would be subjected to, was slightly different and contained a surprise element. Experiments were conducted 6 days per week, 3 days family group and 3 days bachelor group randomized, giving a total of 8 weeks all 3 treatments each week in a randomized distribution. When the first chimpanzee approached the vicinity of the apparatus (i.e. was within an approximate range of 10 m and had established visual contact with the apparatus) observers started recording behaviour for 20 continuous minutes. Data collection was obtained through the register of video sessions with a total of 48 hours of direct observation, subsequently submitted to behaviour coding. The behaviour responses to these experimentally generated emotional situations met expected behaviours (e.g. play, affiliative) in the positive condition sessions; the neutral experiments elicited mostly the behaviours expected in the positive condition; the stimuli assumed to elicited aversive responses (e.g. avoidance, flee, scream) in the negative condition varied substantially in the elicited responses: some as expected elicited negative responses, but most had the same behaviour outcomes as the positive condition. To conclude, this study demonstrates the difficulty to assess in daily management the most appropriate materials to achieve our goals of behavioural change, either in enrichment programmes or in experimental projects, and highlights the need to inventory what constitutes positive and negative stimuli for a chimpanzee.