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Our understanding of large-scale climatic phenomena and dynamics of large herbivore populations comes principally from research in northern regions with temperate, seasonal climate and animal communities with relatively low species diversity. To assess the generality of that perspective, we investigated effects of El Nino-Southern Oscillation (ENSO) on population dynamics of African buffalo Syncerus caff er inhabiting a semi-arid savanna with variable rainfall. We used linear and nonlinear-threshold models to investigate relationships between population parameters and explanatory variables affecting forage conditions (seasonal rainfall, Southern Oscillation Index [SOI]). El Nino-related droughts in 1982-1983 and 1991-1992 were associated with strongly negative population change, a pattern expected to coincide with a decrease in normally high and constant adult survival. Consistent with that nonlinear pattern, we detected threshold relationships between wet-season rainfall and population change. Juvenile recruitment was described best by linear relationships with dry-season. Because ENSO operates primarily through wet-season rainfall, whereas population dynamics were also related to dry-season rainfall, SOI did not have the predictive ability of individual weather components.