These baboon-size animals are the world's most terrestrial primates—except for humans. As grass-eaters, they are the last surviving species of ancient grazing primates that were once numerous. Geladas spend most of their day sitting down, plucking and munching on grasses. They have fatty rear ends, much like human buttocks, which seem well adapted to this activity.
Theropithecus gelada live in small family units of one male and three to six females. Though males are larger and more colorful, females dominate gelada societies. When an aging male begins to decline, the females in his family decide when he will be replaced by a younger rival—though the male will do all he can do to drive off such competition.
Gelada family units often combine to form large foraging bands of 30 to 350 animals. When food is abundant as many as 670 geladas have been seen together. About 100,000 to 200,000 gelada monkeys survive, but even their remote mountain locales are feeling the effects of encroaching agriculture that threatens the grasslands. Indigenous peoples also hunt gelada and use their impressive manes in traditional coming-of-age ceremonies.