Gelada Monkey - A Monotypic Species
The gelada monkey is also known as the ‘bleeding heart’ monkey. Its taxonomic name is Theropithecus gelada. Like the pronghorn, numbat and moose, it is a monotypic species, the only survivor of its genus.
It gets its bleeding heart name from a bare patch of skin on the chest which varies from pink to red depending on the social status of the male and the reproductive state of the female. The gelada monkey is the last of a long line of grazing primates.
Widespread famine in the area together with political upheaval has meant that very little study has been done on these large herds of monkeys.
Geladas are found on the mountainous peaks of northern Ethiopia.
The towering Simien Mountains contain grassed plateaux which provide food for the geladas. These grasslands are 6,000 to 16,000 feet above sea level. Researchers need to be keen as it can take three inland flights, a six-hour drive and a 13-hour hike to reach this beautiful highland plateau. The skyline reveals jagged volcanic plugs split by deep channels and gorges.
Geladas are visually arresting with leathery complexions and huge canines. Males are twice the size of females and weigh 50 to 60 pound. The pelage is coarse and buff to dark brown in colour. The eyelids are pale and the tail shorter than the body and head with a tuft at the end. The extremities are almost black.
The bare patch on the chest is hourglass shaped and ranges from pink to bright red, depending on hormone levels. Pearl-like knobs of skin surround the patch on females and these blister during oestrus. Other monkeys signal sexual readiness with swellings on the rump but the gelada spends so much time sitting on his rump feeding that evolution has supplied another signal.Credit: By BluesyPete (Own work) [GFDL (www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (www.creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Although the gelada has ischial callosities (hard leathery skin) on the rump, these are not as colourful as those of other species.
The gelada has long thumbs. These have a high degree of precision when used for gripping grasses, the highest of any primate bar humans. The fingers are short and strong, ideal for digging. Their dentition is specialised for their grass- and seed-eating diet although the canines of the male are longer than those of a lion. The males bare their canines at each other in threat gestures. The females’ canines are short. Males have a long, luxurious mane on the head and shoulders which forms a flowing cape. There is no fur on the face. In contrast, the females are close-cropped.
Geladas have a very varied vocal repertoire, one of the most varied of all the primates. From explosive barks to soft grunts and high-pitched cries, the gelada uses them all.
Foraging takes place during the day but at night the monkeys go over the edges of the cliffs to sleep on small ledges, out of reach of leopards and hyenas. They move in huge herds of up to 1,200 individuals. Most communication though is between a male leader, his harem of 2 to 12 females and their offspring. The females are related to each other. The male is expected to groom each female as well as protecting them as a group. The females are not above ganging up against their leader if he becomes lax in his duties.
Bachelor groups lurk on the edges of the harems.Credit: By BluesyPete (Own work) [GFDL (www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (www.creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Ritual displays take place with the leader challenging a bachelor who roars back. The leader then tears around with the bachelor in pursuit. When the leader tires of the charade, he leaps into a tree and shrieks at the bachelor who then wanders off. The shriek is always a triple ‘yeow’.
From time to time, a bachelor group will take turns chasing the leader. The triple call of the leader at the end of each chase gradually becomes less strident and the bachelors sense this weakening.
When he is at the point of exhaustion, a contender steps forward and a vicious fight ensues which may result in one of the pair being mortally wounded. The canines are brought into play, hair is pulled and there is much scratching and biting. A vanquished leader may be allowed to remain with the group but loses mating rights and within hours his chest begins to fade.
However it is the females who decide the order of the day and where grazing will take place. A female may also leave a harem and go off with one of the bachelor group even if he hasn’t won a fight with the leader.
Sunbathing is a ritualistic activity in the morning as is social activity and grooming between the members of the harem. The bulk of the day is spent feeding with more social interaction towards the end of the day before the monkeys descend to the sleeping sites over the edges of the cliff.
They are one of the most terrestrial of the primates and feed almost exclusively on the ground. The monkey squats, feeds then shuffles forward bipedally without changing its posture. This allows almost continuous feeding.
The gelada is herbivorous (or graminivorous – grass/grass-seed eating) and spends hours each day pulling up grass to eat. The fescue grasses are soft and rich in protein. Geladas use both hands to pluck up to 150 blades of grass a minute. Precise manipulation between thumb and forefinger ensures only the best grass is eaten.
Depending on local conditions, flowers, fruits, creepers and herbs may be eaten and rhizomes and roots dug up. Insects are eaten only when readily available.
Habitat loss is the major problem for the gelada with land being increasingly converted into farmlands. Goats, sheep and cattle compete for grass. Some areas of their habitat are now under cultivation and the gelada will sometimes move into the cropped area to forage. Potential and actual predators include dogs, leopards, jackals, hyenas and servals. Geladas normally flee from threats but males have been seen to confront and/or surround predators including leopards. Many habitats are now in closer proximity to human habitations and predation pressure is not high.
Geladas are not endangered at the moment although there is little data on how many of these monkeys exist.