There are only about 2,000 Roloway Monkeys left so of course stupid fucking assholes are hunting the creature for the bushmeat trade. Also, habitat loss is a problem.

Institute for Wildlife Studies

The Roloway guenon is one of the three most endangered monkeys of Ghana, on the west coast of Africa. Roloways are an arboreal species found primarily in undisturbed, mature forests and seem unable to adapt to most habitat changes.

A recent decline of roloway monkeys is most likely related to the decline in forest habitats and deforestation. In the past 100 years, Ghana has lost 80% of its forested lands. The monkeys are also endangered by extensive "bushmeat" hunting. Over 800 tons of bushmeat are sold in Ghana's markets every year. This is equivalent to the weight of 160,000 monkeys or 200 elephants.

The Institute's researcher Lindsay Magnuson conducted a field study of the endangered roloway in its native habitat in Ghana. Lindsay collected information on the habitat use of the Roloway guenon and its relationship to habitat disturbance, hunting pressure, and other environmental factors. Lindsay conducted field surveys in the Ankasa Resource Reserve in southeastern Ghana. This site has one of the highest densities of Roloways in Ghana and shows the most promise for a long-term scientific study of this species. In addition, Lindsay provided education to local people about the ecology of endangered species and the benefits of local conservation.

Wikipedia - Roloway monkey

NewScientist.com - We're pushing 28,000 species closer to extinction