Guatemalan black howlers live in stable troops composed of one or two adult males, a few breeding females, and their offspring, with an average group size of between four and six individuals (2) (6). Groups of bachelor males also exist, the members of which will fight resident males for possession of their troop and access to breeding females (6). The territory of each troop ranges between 3 and 25 hectares, depending upon the size of the group (10). Single offspring are usual, born after a gestation period of 180 – 194 days (2). Leaves and fruit form the bulk of the diet, although flowers and insects may also be eaten. Like other members of its genus, the Guatemalan black howler has large salivary glands that help to break down the tannins in the leaves they eat (6). This monkey is mainly active in the morning and evening, but also remains busy throughout the day (5).