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The study of lateralisation has taken several forms ranging from investigating morphological asymmetries to research on lateralised motor and perceptual functions with many studies successfully evidencing lateralisation in a variety of species. This study, featuring three species (olive baboons, rhesus macaques, and spotted hyaenas) investigated visual field biases with the aim of determining whether emotional valence underpins these biases whilst also considering the influence of a number of other factors such as emotional intensity, age, sex, rank, and, for the first time, oestrus cycles (olive baboons only). This study aimed to establish whether Campbell’s (1982) Right Hemisphere Hypothesis or Silberman & Weingartner’s (1986) Valence Hypothesis offered the more valid theory for the lateralisation of emotion by considering interactions across the full spectrum of emotion – a question the almost exclusive investigation of negatively affective scenarios by previous studies has been unable to answer. Furthermore, this study provided a new methodology for investigating behavioural lateralisation by suggesting that separating the visual spectrum into five fields (extreme left, mid left, centre, mid right and extreme right) allows a more accurate insight into the lateralisation of visual perception than the traditional hemifield model. Finally, a more conservative method is proposed for analysing behavioural data in future studies from this field and suggests that these methods provide a more accurate representation of the lateralisation of emotion than those previously employed. A population-level left side bias was found for the spotted hyaenas, thus providing the first evidence of significantly lateralised behaviour in a large carnivore and, for this species at least, lending some support to Campbell’s (1982) Right Hemisphere hypothesis but as population-level biases were not found for either of the other species it may be premature to suggest this support is unequivocal. Significant age effects were found in two species as adult olive baboons and spotted hyaenas were both found to express significant left side biases. Spotted hyaenas were also found to express significant left side biases for females, dominant individuals, high intensity interactions, and sexual valence interactions whilst olive baboons expressed a significant left side bias during negative valence behaviours but no significant lateral biases were found in any context for rhesus macaques. In olive baboons behaviours performed by males and those of a low intensity were found to occur more frequently in the mid and central visual fields and neutral valence behaviours were less occurrent in the extreme visual fields whilst in spotted hyaenas sexual, positive and negative valence behaviours were significantly less centralised than neutral valence behaviours. Non-oestrus adult female olive baboons were significantly more strongly lateralised than in-oestrus females, thus suggesting an influence of sex hormones upon lateralisation that may also have been apparent from the hyaena data, particularly regarding the significant lateral biases observed for females and dominant individuals. Finally, this thesis discusses a number of methodological issues that were encountered during this study and provides recommendations for future research in this field. Namely, this thesis provides an updated method for calculating laterality bias that is much more suitable for species with binocular vision and details a novel method of assessing visual field preferences by considering central and peripheral visual fields as separate entities. Furthermore, this thesis suggests that the weighted method designed and implemented for this study provides a much more accurate methodological foundation for analyses which avoids the caveats that may have affected previous research and thus provides a considerably more robust template that should be encouraged for any similar subsequent studies.

This thesis uses a number of novel methods to investigate how various measures of individual energetic status and condition vary within and between two troops of olive baboons (Papio hamadryas anubis) in Gashaka Gumti National Park, Nigeria. One troop is entirely wild-feeding whilst the other supplements its diet with crop-raiding, behaviour previously suggested to provide energetic benefits. Observations of activity budgets and feeding behaviour were combined with nutritional analyses of food samples to estimate energetic intake and expenditure amongst adult female baboons. Glucocorticoid (stress hormone), progesterone (reproductive hormone) and urinary C-peptide (an indicator of energetic status) levels of the same animals were assessed via analyses of faecal and urine samples. These data were used to investigate the effect of food-enhancement, between troops; the effect of reproductive state and rank, within troops; and the effect of variation in weather conditions and food availability across the nine month study period. Benefits of crop-raiding behaviour included elevated resting time, energy intake rates and reproductive success, and reduced feeding time and glucocorticoid levels in the crop-raiding troop as compared to the wild-feeding troop. Food-enhancement also appears to have buffered the crop-raiding troop’s energetic status and stress levels against the effects of environmental stressors. Within troops, energy intake and expenditure rates varied between individuals in different reproductive states but not different ranks and neither factor significantly affected C-peptide or glucocorticoid levels. Rainfall had a considerable but variable influence on the baboons, being correlated with both positive and negative aspects of their behaviour and condition. Gashaka represents an extreme habitat for baboons, with high rainfall creating both a food and disease rich environment. The results of this study suggest that while low to moderate rainfall brings benefits, via increased food availability, heavy rainfall exerts a negative influence on the Gashaka baboons via increased disease risk.