Primarily a grazer , the oribi prefer fresh grasses and browses occasionally . Grasses can constitute up to 90 % of the diet ; preferred varieties include Andropogon , Eulalia , Hyparrhenia , Loudetia , Pennisetum and Themeda species . Mineral licks are also visited regularly . Oribi have been observed feeding on flowers and Boletus mushrooms . Groups of oribi congregate in the rainy season , when grasses are abundant .