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.
Reproduction and Parenting
When in estrus, the female points her posterior towards a male and raises it, moving her tail to one side. The male then approaches the female and inspects her chest and genital areas. A female will copulate up to five times per day, usually around midday. Breeding and reproduction can occur at any time of the year, although some areas have birth peaks.
Most births occur at night. Newborn infants have red faces and closed eyes, and they are covered in black hair.] On average, newborn infants weigh 464 g (16.4 oz). Females that have just given birth stay on the periphery of the reproductive unit. Other adult females may take an interest in the infants and even kidnap them. An infant is carried on its mother’s belly for the first five weeks, and thereafter on her back. Infants can move independently at around five months old. A subordinate male in a reproductive unit may help care for an infant when it is six months old. When herds form, juveniles and infants may gather into play groups of around ten individuals. When males reach puberty, they gather into unstable groups independent of the reproductive units. Females sexually mature at around three years, but do not give birth for another year. Males reach puberty at about four or five years, but they are usually unable to reproduce because of social constraints and wait until they are about eight to ten years old. Average life span in the wild is 19 years.
Adult geladas use a diverse repertoire of vocalizations for various purposes, such as: contact, reassurance, appeasement, solicitation, ambivalence, aggression and defense. The level of complexity of these vocalizations is thought to near that of humans. They sit around and chatter at each other, signifying to those around that they matter, in a way, to the individual "speaking". To some extent, calls are related to the status of an individual. In addition, females have calls signaling their estrus. Geladas communicate through gestures, as well. They display threats by flipping their upper lips back on their nostrils to display their teeth and gums, and by pulling back their scalps to display the pale eyelids. A gelada submits by fleeing or presenting itself.