A large and unusual monkey restricted to the mountains of central Ethiopia is the gelada (Theropithecus gelada). Like that of its close relatives the baboons and drills, gelada social structure is very complex and dynamic. In this species the social units seem to be held together mostly by the bonds between individuals of the same sex, especially females, who tend to associate more among themselves. Nights are spent sleeping on the faces of rocky gorges, where the animals feel secure and from where they never stray far. During the day they forage for grasses, from which they derive practically all of their nourishment -- a diet unique among primates. The adult male is easily distinguished by his long golden mane and whiskers, and a red triangle of bare skin framed by short grizzled fur on his chest. Perching elsewhere on the cliff are a lizard (Agama sp.) and a pectinator (Pectinator spekei), an unusual rodent distantly related to the chinchilla.