A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Okaukuejo 1993 / This study was designed to investigate the eco-physiology of baboons (Papio cynocephalus ursinus) in a troop living in the Kuiseb River canyon of the central Namib desert, Namibia. Answers were sought for two major questions: what Were the baboons prospects for survival and were there special adaptations allowing for their survival in their desert environment? To answer the former, life history phenomena of individuals and demographic changes within the troop were studied over a six year period. Results showed that the troop was not self-sustaining. Ectco-parasite infestations killed the majority of infants born to high ranking female baboons, while infant kidnapping by high ranking females killed most lower ranking females' infants. The high infant mortality appeared to affect the behaviour of adult male baboons in the troop, causing non-paternal males to fight harder to maintain a rank with reproductive opportunities, usually with serious wounding or death as a consequence. Answers to the latter question involved investigation into the baboons feeding patterns and diet, body temperature regulation, water flux rates and methods of body water conservation. Despite their desert environment, the baboons had access to plants of high water content and Were not dependent on free water intake. Plant foods also had low electrolyte concentrations. Body temparetures of three free-ranging baboons recorded by intraperitoneal radio tolemeters were remarkably labile, indicating an adaptive heterothermy. The baboons appeared to employ evaporative cooling only when water was available to drink and used cool sub-surface sand to slow their body temperature rises. water flux rates determined using tritiated water of three free-ranging baboons were not different to those of baboons from elsewhere. Acquisition of free water at times of water scarcity was strictly rank related. Body water conservation was apparently achieved through a combination of factors: urine concentration of Kuiseb baboons increased significantly when they were water deprived. The kidneys of the Kuiseb baboons, obtained from baboons that died naturally were anatomically significantly different and head greater urine concentrating abilities than the kidneys Of baboons from the northern Transvaal, South Africa. Kuiseb baboons showed efficient faecal water conservation, similar to other desert adapted mammals, Body water also was apparently conserved by engaging in water conservative behaviour, predominantly inactivity.