in association with other species, particularly oryx, Grant's gazelle, Burchell's zebra and topi. They avoid Coke's hartebeest, buffalo and elephant. Whilst hirola avoid direct association with livestock, they reportedly prefer the short grass in areas where livestock have grazed. Social structure and reproduction Female hirola give birth alone and may remain separate from the herd for up to two months, making them vulnerable to predation. Eventually the female will rejoin a nursery herd consisting of females and their young. Nursery herds number from 5 to 40 although the mean herd size is 7-9. They are usually accompanied by an adult male. Young hirola leave the nursery herd at around nine months of age and form various temporary associations. They may gather together in mixed or single sex herds of up to three individuals; sub-adult or subordinate adult males may form bachelor herds of 2-38 individuals; female sub-adults may join an adult male and; if no other hirola are present, young hirola may attach themselves to a herd of Grant's gazelles or simply spend most of their time alone. Adult males attempt to secure a territory on good pasture. These territories are up to and are marked with dung, secretions from the sub-orbital glands and by stamping grounds where males scrape the soil with their hooves and slash the vegetation with their horns. It has been suggested that at low population densities adult males abandon territory defence and will instead follow a nursery herd. Nursery herds do not defend a territory but do have home ranges which overlap the territories of several adult males. The size of a nursery herd's home range varies from with a mean size of . Nursery herds are relatively stable but bachelor herds are very unstable with a fission fusion dynamic. In the 1970s hirola were observed forming aggregations of up to 300 individuals to take advantage of scarce, but spatially clumped, resources during the dry season (Bunderson, 1985). Information is lacking on male territoriality and how it relates to mating success, how and when hirola join a herd and how new herds are established (Butynski, 2000). Hirola are seasonal breeders with young being born from September to November. Data on age of sexual maturity and gestation period are not available for wild hirola however in captivity gestation was around 7.5 months (227–242 days) with one female mating at 1.4 years old and giving birth at