Males compete among themselves for access to females and generally defend territories in which they maintain a harem of about 7 or 8 females. Male posturing includes head-flagging, marking of grass stems with preorbital glands, ground scraping with their hooves, and dung accumulations. Aggressive fighting between males is different from play-fighting by their stance. Earnest fights take place on their knees, whereas play-fighting takes place in an upright position.
Mating System: polygynous
Hirolas mate at the beginning of the long rainy season in March or April and gives birth at the beginning of the short rainy season in October and November. Gestation typically lasts 7 to 8 months and a single calf is born, though twins are possible. Females become sexually mature at 2 to 3 years of age, while males do not mate until they are large enough and dominant enough to successfully compete with other males, usually between 3 to 4 year old.
Breeding interval: Hirolas breed once yearly.
Breeding season: Breeding occurs in March and April.
Range number of offspring: 1 (low) .
Average number of offspring: 1.
Range gestation period: 7 to 8 months.
Range age at sexual or reproductive maturity (female): 2 to 3 years.
Range age at sexual or reproductive maturity (male): 3 to 4 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous
Females nurse and care for their young, who are capable of standing and running soon after birth. Calving females will separate from the group for the two weeks following birth. During this time the female and the calf are vulnerable to predation. When the calf has reached yearling status, it separates from the herd to join a sub group of yearlings.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female); post-independence association with parents