Geladas are easily recognizable primates due to the identifying hairless patches of skin on their chests. During the mating season, these chest patches acquire bright crimson coloration in females. These primates are sometimes called Gelada baboons. However, they aren't baboons. Instead, Geladas form a separate genus of their own. Additionally, they are the last surviving member of a grass-grazing primate group, members of which were abundant and widespread in the past. Geladas are well adapted to their terrestrial lifestyle. These animals are specialist grass-eating primates. Their small, powerful fingers are designed for pulling grass, while small incisors allow them to chew it. When eating, Geladas move around with characteristic shuffle gait. When walking, they use all of their four limbs and slide their feet without changing the body posture, so that the bright red patch on their chest is conspicuous, whereas the rump remains hidden. Captive Geladas are known to live more than 30 years. Life expectancy of those in the wild in unknown, although it's believed to be shorter than that of captive individuals.
The natural range of this species is restricted to Ethiopia, where these animals mainly occur in in the Semien Mountains National Park. During the nighttime hours, they typically sleep on rocky cliffs and outcrops. In the morning, Geladas typically look for food in nearby grasslands, at heights of 2,000 - 5,000 meters above sea level.
Geladas are diurnal and highly social animals, forming so-called one male units (OMUs). These are female-led groups that consist of a single male and multiple females with their young. When a male from the outside challenges the male of the OMU in order to displace it, females of the group may support or oppose both of them, accepting the winning male and fiercely driving away the defeated one. Various OMUs occasionally share the same area, thus forming larger units called bands. As these animals are non-territorial, they may be observed grazing in separate bands in areas with abundant food without any conflicts. Males and females can often be observed grooming each other. In general, all members of the community participate in grooming, which enhances social bonds within the OMU.
Geladas are polygynous, which means that one male gets an exclusive right to mating with multiple females. Although Geladas can mate at any time of the year, births appear to peak during the rainy season. Gestation period lasts for 5 - 6 months, yielding a single baby, which feeds upon maternal milk for 1 - 1.5 years. The infant is mainly cared by its mother, who will carry, groom, nurse and protect the baby, until the latter reaches the age of independence. Meanwhile, the father will take little part in rearing its offspring. Males of this species are sexually mature at 5 - 7 years old, whereas females are ready to produce young at 4 - 5 years old.
One of the biggest threats to the population of this species is habitat reduction due to development of agriculture. Additionally, Geladas are considered pests and thus shot because of destructing crops.
According to the IUCN Red List, the total population of Geladas is around 200,000 animals. Currently, this species is classified as Least Concern (LC) but its numbers are decreasing.
On one hand, due to their grass-based diet, Geladas control plant communities of their range. On the other hand, they contribute to aeration of soil through their habit of digging for roots, tubers and grass rhizomes. Additionally, Geladas may be an important prey species for many local predators.