Typically diurnal , the oribi is active mainly during the day . Small herds of up to four members are common ; males defend their group 's territory , 25 – 100 hectares ( 62 – 247 acres ) large . The oribi is primarily a grazer , and prefer fresh grasses and browses occasionally . A seasonal breeder , the time when mating occur vary geographically . Unlike all other small antelopes , oribi can exhibit three types of mating systems , depending on the habitat – polyandry , polygyny and polygynandry . Gestation last for six to seven months , following which a single calf is born ; births peak from November to December in southern Africa . Weaning take place at four to five months .