The foraging ecology of a band of gelada monkeys (Theropithecus gelada) was studied in the field at Sankaber, Ethiopia, for 14 months. The field site is at high altitude (3300m) and experiences severe variation in climatic and vegetational conditions across distinct wet and dry seasons and between different microhabitats. Gelada live in a complex fission/fusion social system and occupy a unique environmental niche as the world's only graminivorous primate species. Research was directed towards examining the ecological parameters affecting the gelada's group-level behavioural ecology. The nature and distribution of gel ada food resources was found to be a more complex and influential selective force than previously acknowledged. Gelada ranging behaviour varied in relation to spatial and temporal variation in food availability and specific small scale weather patterns, but not in relation to the distribution of sleeping sites, refuges or water sources. Group size and day journey length covaried significantly between seasons and months and the strength of the correlation between the two variables was determined by levels of food availability. The rate at which the main gel ada study band underwent fission or fusion correlated to the degree in which food was patchily distributed but not direct levels of food availability. Distribution of food sources varied significantly between habitats as did levels of visibility. Gelada alarm and flight response rates were found to correlate more strongly to levels of visibility under 10 metres within each habitat than mean levels of visibility per se. Both males and females spent significantly more time feeding, (and feeding on subterranean food items specifically) in the dry season, resulting in a slightly higher mean daily calorific intake than in the wet season. It is suggested that the dry season does not represent a 'nutritional bottleneck' to the gel ada as previously thought, but does constitute a period of increased energy requirements due to seasonal variation in lactation and thermoregulation demands