Age-sex analysis of activity budget, diet, and positional behavior in Alouatta caraya in an orchard forest

Howlers (Alouatta spp.) spend more than half of the daytime resting and their diet consists predominantly of leaves. Associated with a general strategy of energy conservation, their positional behavior is characterized by quadrupedalism as the major locomotor mode, and sitting as the most common resting and feeding posture. However, researchers have sparse information on the degree to which age-sex classes fit the generic trends and the influence of habitat structure on them. We compare the activity budget, dietary composition, and positional behavior by age-sex or age classes in a group of black-and-gold howlers (Alouatta caraya) in a small orchard forest. We collected 26,474 behavioral records via instantaneous scan sampling over 1 yr. The main activity was resting (56%) and the diet comprised mainly leaves (82%); sitting was the most adopted feeding (61%) and resting (52%) posture, and walking was the most prevalent locomotor mode (38%). There are age-sex differences for all major behaviors. Whereas resting tended to increase with body size, moving decreased. We observed no difference in the consumption of major plant parts. There were ontogenetic differences in most positional behaviors. Sitting increased from infants to adults during feeding, whereas the opposite occurred for bridging and hanging. During resting, infants curled more and lay less than the other classes did, whereas adults engaged in more sitting. Adults and subadults walked more than individuals of other ages did; infants climbed and bridged more than others did; and, there were opposing trends in leaping and descending. Habitat structure is a partial explanation of the locomotor behavior of black-and-gold howlers.