Relative Dominance and Resource Availability Mediate Mantled Howler (Alouatta palliata) Spatial Responses to Neighbors’ Loud Calls

Many animals generate long-distance vocalizations (“loud calls”) that have been hypothesized to mediate spatial interactions. Howls by mantled howlers (Alouatta palliata), specifically, are hypothesized to function in group spacing, but the mechanism by which this is accomplished remains unclear. In this study, I evaluated the role of naturally occurring howls in mediating mantled howler intergroup spatial interactions on Barro Colorado Island, Panama. Multivariate analyses examined relationships between social and environmental contextual variables and the likelihood that a group would approach or avoid a neighboring group’s howl. Mantled howlers were more likely to approach howling neighbors when fruit and flower availability was limited. Relative dominance was also a highly significant predictor of approach, though the relationship ran contrary to expectations. Groups were more likely to approach howling neighbors higher in the established dominance hierarchy than those lower down, possibly reflecting priority access of more dominant groups to higher quality resources. Other variables tested, including numeric odds, vocalization intensity, infanticide risk, and location of the howling group, were not significant predictors of spatial response. These findings are consistent with the assertion that howls contain identifying information and highlight the importance of including contextual variables in multivariate analyses of spatial responses to loud calls. These results also indicate potential contrasts between observational and playback studies by suggesting that howl location may play a greater role in responses to simulated intruders than to known neighbor groups, and that relative dominance may provide a more salient measure of competitive ability than numeric odds among groups with interaction histories.