ROLE OF LOUD CALLS IN BROWN HOWLERS, ALOUATTA-FUSCA

The loud calls of brown howler monkeys were studied during a year at t he Santa Genebra Reserve, in southeastern Brazil. The study group emit ted roars and barks on a total of 47 occasions, the majority of which (92%) were restricted to intergroup visual encounters. Loud calls were also elicited by the roars of distant groups (6%) and during intragro up agonistic interactions (2%). Intergroup visual encounters (n = 42) occurred predominantly in seldom used quadrats of the study group home range. In these instances, the loud calls were produced chiefly by th e adult male alone (69% of cases), while the study group's two adult f emales joined the male in the remaining cases. Intergroup physical agg ression, such as chase and displacement, was observed during 15 encoun ters (35% of cases). A dawn chorus does not occur in Santa Genebra-the loud calls were heard most frequently in mid-morning and again during mid-afternoon-and they were more abundant during the dry season, when the availability of food (new leaves) in the forest was lower. The da ta presented here provide some support for the hypothesis that roars o f howler adult males are used in assessment of opponents, providing an alternative to energetically expensive chases and fights. However, gi ven the relatively high rate of physical aggression observed during in tergroup encounters, a result probably related to the high density of howlers and the consequent high frequency of intergroup encounters obs erved in this forest (0.7/day), ritualized aggression, in the form of loud calling, is apparently often insufficient to settle disputes. (C) 1995 Wiley-Liss, Inc.