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. They are found in evergreen forests and montane bamboo forests, and lives largely in the forest canopy, which provides both food and shelter. They are very dependent on humid, shady areas with plenty of water and eat mainly fruit and leaves, but will take some slower-moving invertebrates. Despite their name, the blue monkey is not noticeably blue; they are mainly olive or grey apart from the face, the blackish cap, feet, and front legs, and the mantle, which is brown, olive, or grey depending on the subspecies. They range from 50 to 65 cm in length, (not including the tail, which is almost as long as the rest of the animal), with females weighing a little over 4 kg and males up to 8 kg. The blue monkeys live in female-philopatric social systems where females stay in their natal groups, while males disperse once they reach adulthood. Group sizes range from 10 to 40, containing only a single adult male. They are often found in groups with other species of monkeys such as the red-tailed monkey and various red colobus monkeys since they sometimes join other monkeys for extra protection. Their groups usually consist of one male with several females and infants, and this gives rise to matrilinear societies. In these female-bonded societies, only 5-15% of their activity budget is occupied by social interactions and the most common social interactions within a group are grooming and playing. Relationships between group members vary: infants interact most frequently with their peers and adult or juvenile females and are rarely seen near adult males. Alloparenting is common among blue monkeys. The most common infant handlers are juvenile females, and usually one infant is carried by a number of alloparents, possibly to allow the infant to learn to socialise at an early stage in life. Their mating system is polygynous, with a corresponding sexual dimorphism in size, as the males are the substantially larger sex. The males mate with more than one female, but the females only mate with one male. The female attracts males to copulate with her through body language. Females normally give birth every two years, during the onset of the warm, rainy season; gestation is around five months, and the infants are born with fur and with their eyes open. Like almost all guenons, the Blue Monkey suffers from a loss of its natural habitat. As well, where pine plantations replace natural forest, they may be treated as a threat by foresters, since they sometimes strip bark from exotic trees in a search for food or moisture. They are also hunted for bushmeat.