A gelada (Theropithecus gelada) perches on a rock in the Ethiopian highlands at sunset. Endemic to Ethiopia, this primate—also known as the 'bleeding-heart baboon' for the distinctive reddish patch on the chest of males, a sign of health and dominance—is the only primate in the world that feeds almost exclusively on grass, which it selects with agile, precise fingers. It spends the nights clinging to rocky ledges along steep escarpments, where the altitude and steep walls protect it from predators. In the background, amid threatening clouds, the jagged peaks of the Simien Mountains rise, a volcanic massif in northern Ethiopia with deep gorges and spectacular basalt cliffs. Declared a UNESCO World Heritage Site, they host the world’s largest concentration of geladas and other endemic species in a high-altitude ecosystem often above 3,000 meters.