The mountain nyala are shy and elusive towards human beings. They spend the night on the edges of forests, feeding part of the time. To avoid human disturbance, they choose to navigate at night. They come out in morning and late afternoon to browse in grasslands. They generally seek cover in woodlands and heather thickets when it is very hot or cold. Feeding may occur in midday, but is interspersed with resting intervals. They tend to come out when it is overcast or raining. In the dry season (November to March), given the dilapidated state of grasslands, the mountain nyala travel up to the wooden areas rich in
ericaceous heath. Four to five individuals may congregate for short intervals of time to form small herds. However, groups containing as many as 100 individuals have been reported from the
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 to engage in aggressive fights, which, if they happen, last only for a brief period.
Flehmen follows vulva-testing.
Gestation lasts for eight to nine months, after which a single calf is born. In the
Bale Mountains National Park, births occur throughout the year, but peak from September to November. Calves remain in cover for the first few weeks after birth. The calves remain close to their mothers for nearly two years. The young females may get pregnant by then. The young males, as they mature by two years, are challenged by other males and driven out of their herds. The lifespan of a mountain nyala is around 15 to 20 years. ==Habitat and distribution==