The blue monkey is a species of Old World monkey native to Central and East Africa, ranging from the upper Congo River basin east to the East African Rift and south to northern Angola and Zambia. It sometimes includes Sykes’, silver, and golden monkeys as subspecies
The Blue Monkey has little hair on its face, and this does sometimes give a blue appearance, but it never has the vivid blue appearance of a mandrill, Like they mainly olive and grey apart from the face which is dark with a place or yellowish patch on the forehead- the diadem from which the species derive its common name, the blackish cap, feet and front leg and the mantle, which is brown, olive or grey depending on the subspecies.
Typical sizes are from 50 to 65 cm in length, not including the tail, which is almost as long as the rest of the animals. Females weigh 4kg and male up to 8kg. The blue monkey is found in evergreen forest and montane bamboo forest and lives in forest canopy.
It is very dependent on humid, shady areas with plenty of water. It eats mainly fruit and leaves, but will take some slower-moving invertebrates. It prefers to live in tall trees which provide both food and shelter, and are therefore, like almost all guenons, suffering from the loss of its natural habitat. Where pine plantations replace natural forest the monkey may be treated as a threat by foresters, since it sometimes strips the bark from exotic trees in a search for food or moisture. It is also hunted for bush meat.
The blue monkeys exist in all national parks in Uganda but they are only absent in Murchison fall Lake mburo national park. The female monkeys live in phliopatric social system and males disperse once they reach Adult. Blue monkey groups usually consist of one male with several females and infants, giving rise to matrilineal societies. Occasionally, solitary males are observed which are probably transient, having left their natal group in search of a new group.
The mating system is polygynous, and there is a corresponding sexual dimorphism in size, with the males substantially the larger sex. Females normally give birth every two years, during the onset of the warm, rainy season; gestation is around 5 months and the infants are born with fur and with their eyes open.
Group size range from 10to 40, containing only a single adult male. It is often found in groups with other species such as red-tailed monkeys and Red colobus monkey.