The Gelada is not in fact peculiar to the Semyen as is the exclusive Walia Ibex, but they are more numerous here than in their other habitats Some live at Debre Sina not far from Addis Ababa and others at Debre Libanos on the way to the Blue Nile; there are also small populations in the Mulu and Bole Valley gorges. But in the Semyen there may be as many as 20,000, and troops of 400 together may be seen. They do not molest humans and, more surprisingly, the local people do not molest them. Thus they are very tame and will allow humans to approach quite close to the troop before moving nearer to the cliff edge.
The Gelada was discovered in 1835 by the explorer Ruppell, who nan;ed it by the local name used by the inhabitants of Gonder region where he first observed it. They are not difficult to study as they are very tame, however, little interest was shown in them until recently, when Patsy and Robin Dunbar made an exhaustive study of their social behaviour. The social behaviour of the apes and monkeys is evidence of a very high degree of intelligence and studies of their rudimentary social structures are proving of considerable value in analysing the origins of human social behaviour.
Geladas live along the edges and steep slopes of precipices. They never move far from the rim and thus their distribution is linear along the escarpment. At night they climb down the steep cliff faces to caves where they roost on ledges, often huddled close together for warmth as Semyen nights are frosty and bitterly cold. Babies cling tight to their mothers even in sleep. In the morning in the warm sun they climb up again to the top of the cliff and spread out to feed. Geladas are mainly vegetarian, living on herbs, grasses and roots, but they also eat insects and locusts. They never eat meat, or hunt or kill even small birds or mammals. As a result of this restricted diet they are obliged to spend a very high percentage of their lives foraging and browsing in order to obtain sufficient nutrients to survive. This may explain why they are so extremely peaceable by nature, with very little squabbling even amongst themselves. They have no natural enemies (except of course, Man, who takes a fair toll with his rifle. The great mane of the adult male is used for traditional headresses by highland warriors).
Apart from feeding, "grooming" is their other main pastime. This entails simply picking through each other's fur. This is not only a friendly and peaceful occupation, but it serves also to establish bonds between various members of a 'harem' and to cement the accepted relationships in the hierachy, between male and female, older and younger members.
The long narrow plateaus of the Semyen slope up- wards from the south until they end in the dizzying precipices of the northern escarpment. This is the haunt of the Walia, and the Gelada do not frequent these vertical cliffs, but the rims of the stupendous gorges and ravines which bisect the plateau. The troops tend to graze the higher moorlands, amongst everlastings, giant lobelias and alchemilla-tussock grass. Never far from the rim, which is their refuge when danger threatens, they disappear over the edge on to the grassy slopes and ledges of the gorge sides. Their grazing ranks are so arranged that the males are always farthest from the edge and thus it is "women and children first" when they have occasion to flee to safety.