Potential functions of long distance calls in population of Alouatta caraya, Chaco, Argentina.

ORUE, M. E; OKLANDER, L.

Bello Horizonte, Minas Gerais, Brasil

Congreso; XII Congresso Brasileiro de Primatologia; 2007

Associação Brasileira de Primatologia

Long-distance calls produced by males are common among vertebrate species. Long calls are emitted by black and gold howler monkey (Alouatta caraya) and appear to have multiple functions related to spacing mechanisms and territoriality. The howl seems to indicate the minimum number of male group members. When fighting is costly, avoiding contests with superior opponents should confer fitness advantages. In order to test the hypothesis that roars of howler adult males are used in assessment of opponents, providing an alternative to energetically expensive chases and fights, I examine whether male’s groups use loud calls to assess relative group fighting ability and whether they modify their responses in relation to advantages/desvantages in number of males howling during the contest. We described the acoustic properties of the roars, the context of occurrence and the potential functions of this vocalization. Over 1 month, acoustical and behavioral data were collected on three free-ranging groups of black and gold howlers inhabiting continuous forest on Isla Brasilera; Chaco, Argentina (27º 20´ S, 58º 40´ W). The results showed absent of spontaneously dawn chorus. Most roars were given during inter-group encounters, at overlapping home range. The duration of the call was longer when the opponents groups had similar numbers of males calling. The data support that roars provide a mechanism for reinforcing occupancy during encounters, and may sometimes serve to settle disputes without chases and fights. However, given the relatively high rate of physical aggression observed during intergroup encounters in previous studies in howlers, a result probably related to the high density of howlers and the consequent high frequency of intergroup encounters observed in this forest (1.22/day), ritualized aggression, in the form of loud calling, is apparently often insufficient to settle disputes.