Gelada

The gelada is large and robust, and it is covered with buff to dark-brown, coarse hair and has a dark face with pale eyelids. Its arms and feet are nearly black. Its short tail ends in a tuft of hair. Adult males have a long, heavy cape of hair on their backs. The gelada has a hairless face with a short muzzle that looks more similar to a chimpanzee's than a baboon's. It can also be physically distinguished from a baboon by the bright patch of skin on its chest. This patch is hourglass-shaped. On males, it is bright red and surrounded by white hair; on females, it is far less pronounced, but when in estrus, the female's patch brightens, and a "necklace" of fluid-filled blisters forms on the patch. This is thought to be analogous to the swollen buttocks common to most baboons experiencing estrus. In addition, females have knobs of skin around their patches. Geladas also have well-developed ischial callosities. Sexual dimorphism is seen in this species; males average 18.5 kg (40.8 lb), while females are smaller, averaging 11 kg (24.3 lb). The head and body length of this species is 50–75 cm (19.7–29.5 in) for both sexes. Tail length is 30–50 cm (11.8–19.7 in). The gelada has several adaptations for its terrestrial and graminivorous (grass-eating) lifestyle. It has small, sturdy fingers adapted for pulling grass and narrow, small incisors adapted for chewing it. …

Geladas are found only in the high grasslands of the deep gorges of the central Ethiopian plateau. They live in elevations 1,800–4,400 m (5,900–14,400 ft) above sea level, using the cliffs for sleeping and montane grasslands for foraging. These grasslands have widely spaced trees and also contain bushes and dense thickets. The highland areas where they live tend to be cooler and less arid than lowland areas. Thus, the geladas usually do not experience the negative effects that the dry season has on food availability. Nevertheless, in some areas, they do experience frost in the dry season, as well as hailstorms in the wet season. Geladas are the only primates that are primarily graminivores and grazers – grass blades make up to 90% of their diet. They eat both the blades and the seeds of grasses. When both blades and seeds are available, geladas prefer the seeds. They eat flowers, rhizomes, and roots when available, using their hands to dig for the latter two. They consume herbs, small plants, fruits, creepers, bushes, and thistles. Insects can be eaten, but only rarely and only if they can easily be obtained. During the dry season, herbs are preferred over grasses. Geladas consume their food more like ungulates than primates, and they can chew their food as effectively as zebra. Geladas are primarily diurnal. At night, they sleep on the ledges of cliffs. …

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). If a new male assumes mastery of a harem, females impregnated by the previous leader have an 80% likelihood of aborting, in a phenomenon known as the Bruce effect. Females come into estrus quickly after giving birth, so males have little incentive for practising infanticide, although it does occur in some communities in the Arsi region of Ethiopia, which may be an incentive for females to abort and avoid investing caring for an infant that will most likely be killed. Females also practice deceptive fertility signalling when conception is unlikely, a strategy to avoid infanticide. Infanticide in geladas remains fairly uncommon, though, compared to many primates that live in one-male units such as gorillas or gray langurs. The females that cancel their pregnancy are thought to bond with the new leader faster. …