any of some dozen species of long-tailed tree-dwelling and generally gregarious monkeys (monkey) native to eastern, central, and western Africa. Colobus monkeys are active during the day and are able to make long leaps between trees. The three genera of colobus are all more or less thumbless and can be distinguished by colour: black-and-white colobus (genus Colobus), red colobus (genus Piliocolobus), and olive colobus (genus Procolobus).

The five or more species of red colobus are brown or black with red markings and are about half a metre (1.6 feet) long, excluding the 40–80-cm tail. In large species, such as the bay colobus (Piliocolobus badius) of West Africa, both sexes average 8 to 8.5 kg, though the Zanzibar red colobus (P. kirkii) weighs only 5.5 kg. Unlike black-and-white colobus, red colobus tend to live in large troops sometimes numbering 60 or more, with each troop including several adult males. Red colobus are not territorial, and they do not have such loud calls or dramatic displays. In many regions they are extremely abundant, but, where their forest habitat has been altered by logging or fire, they are much less resilient than black-and-white colobus. Several races of the red colobus are endangered (endangered species), and some subspecies of red colobus have apparently become extinct since the middle of the 20th century. The other colobus species are declining in population and are variously listed as vulnerable or rare. The olive colobus (Procolobus verus) is a small monkey, weighing only 4.5 kg, with short olive-coloured fur. It lives in West Africa, where it is not especially rare but is very quiet and secretive and therefore seldom seen. Neither red nor olive colobus survive very long in captivity.