The Gelada (Theropithecus gelada) is a species of Old World monkey, found only in the Ethiopian Highlands of Ethiopia and Eritrea. It has large populations in the Semien Mountains. Like its close relative, the baboon, it stays on land and spends its time foraging in grasslands. Gelada can be distinguished from baboons by the bright patch of skin on its chest. The patch is hourglass-shaped. On males, it is bright red and surrounded by white hair. On females, the patch is far less pronounced. However, when in heat, the female’s patch will brighten. The “necklace” of fluid-filled blisters forms on the patch. This is thought to be similar to the swelling on the buttocks during reproductive changes, which is common to most baboons. This modification probably evolved because the Gelada spends almost all its life in a sitting position. It has the buttocks hidden, so that it cannot serve as a visual cue. The male Gelada’s tail is about as long as the body and densely tufted at the tip. It also has a long and flowing mantle and mane.
The Gelada lives in small groups with one male, and several females and their offspring. These small bands often join together to feed. They create groups of upwards of 350 individual monkeys. At especially good feeding spots, group of upwards of 670 individuals have been observed.
The Gelada is primarily a grass-eater. It eats every part of the plant, from the seeds, to the roots, to the stalk. It has the most well developed opposable thumbs of any of the Old World monkeys. This allows it to pick apart grasses with great dexterity to find the nourishing parts. It has also been known to eat fruit on occasion.
Although not listed as endangered, only 50 to 60,000 Geladas are known to exist. Hunting and habitat destruction have forced the Gelada into areas formerly inhabited by the Olive Baboon. Hybridization between the two groups has been observed. In the southern part of the Amhara plateau, Gelada males are killed every two years in order to use their manes in a coming-of-age ceremony. The loss of much of the adult male population on a regular basis has disrupted the population of the species.