Bale Zone, composed of several family units moving in and out periodically. Size and longevity of such large herds depends upon the season, habitat type and the time of the day. Female and juvenile groups have adult females accompanied by a calf of her previous year and another of the current year. These groups are led by adult males, depending on the presence of oestrus. Bachelor herds are formed by non-dominant adult bulls and young males, consisting of up to 13 individuals. Mixed sex groups may also be formed. Old bulls tend to lead a solitary life, though they may occasionally visit female herds looking for females in oestrus. Dominance hierarchies are observed in both sexes. Males are not territorial, and have home ranges covering in the wet season. Females and juveniles, on the other hand, occupy much smaller ranges of about in the wet season. Dry season ranges are much larger than the wet season ones for both sexes. Males often wrestle using their horns. Though usually silent, the mountain nyala may "cough" noticing a potential threat, or utter a low bark if the threat is more serious. The leopard is the main predator of the mountain nyala. Diet Primarily a browser, the mountain nyala may switch to grazing occasionally. It feeds on low-height herbs, bushes, shrubs and general foliage. They might even eat lichens, ferns and aquatic plants. Grasses are specially preferred during the early wet season. They pick up fallen leaves and use their horns to reach higher branches. Favoured species include Artemisia afra (African wormwood), Hypericum revolutum, Kniphofia foliosa, Solanum sessilistellatum and Hagenia abyssinica leaves. They prefer Alchemilla rotti, Helichrysum splendidum and lower foliage of Lobelia rhynchopetalum. Reproduction Females start mating at two years of age, and males too become sexually mature by that time. Sexual dimorphism, larger home ranges for males, and a female-biased population indicate polygyny in the species. The mountain nyala breed throughout the year, but the peak occurs in December. Prior to and during the breeding season the adult males tend to get associated with mixed sex herds. Bulls continuously follow receptive females and test their vulvas. Three to four males may seek a single female, and, if equally ranked in hierarchy, may engage in circling displays. In these displays the males move very slowly and stiffly, with the crest on the back erect and the tail raised. They are less likely