Wikipedia:
The Patas Monkey (Erythrocebus patas) is a ground-dwelling monkey distributed over West Africa, and into East Africa. It is the only species classified in the genus Erythrocebus. The Patas Monkey avoids dense woodlands and lives in more open savanna and semi-deserts. The Patas Monkey grows to 85 cm (33 in) in length, excluding the tail, which measures 75 cm (30 in) Reaching speeds of 55 km/h (34 mph), it is the fastest runner among the primates.

This monkey lives in groups of about twelve individuals. There is a loose matrilineal dominance rank. The group contains just one adult male for most of the year.[3] During the breeding season, there are multi-male influxes into the group. Once juvenile males reach sexual maturity (around the age of 4 years old) they leave the group, usually joining all the all-male groups. Patas monkeys feed on insects, gum, seeds, and tubers.
The role of the male in the group is that of guard. When a threat approaches the group, he puts on a loud vocal display and vigorously shakes trees and bushes while moving away from the main group to lure the threat away. The adult females in the group initiate movement of the group with the male following their lead.[3]
There is some confusion surrounding the number of valid subspecies, with some listing four,[4] and others listing two; the western Erythrocebus patas patas (Common Patas; with a black nose) and the eastern Erythrocebus patas pyrrhonotus (Nisnas; with a white nose). Others, however, have suggested that at least some of the features used to separate these subspecies merely are variations in the female's facial pattern during pregnancy, and therefore tentatively consider this species monotypic.[1]