The spread of human activity, settlement and land fragmentation threatens the migrations of large migratory ungulates in Africa. Modelling the migrations gives conservationists a tool for building scenarios of the threats and containment options. We propose a simple spatially explicit mathematical model of ungulate migrations based on the seasonal distribution of vegetation quantity and quality and allometric models of diet. We use the seasonal movements of selected migrants in relation to vegetation in the Amboseli ecosystem, Kenya. Parameters estimation was done by fitting the model to long term movement patterns by minimizing total least square errors. The model suggests that the migrants broadly track the shifting patterns of vegetation growth and senescence according to body size.