 Impala feed on soft and nutritious grasses such as Digitaria <unk> ; tough , tall grasses , such as Heteropogon contortus and Themeda triandra , are typically avoided . Impala on the periphery of the herds are generally more vigilant against predators than those feeding in the centre ; a foraging individual will try to defend the patch it is feeding on by lowering its head . A study revealed that time spent in foraging reaches a maximum of 75 @.@ 5 % of the day in the late dry season , decreases through the rainy season , and is minimal in the early dry season ( 57 @.@ 8 % ) . 
