Evidence for semantic communication in titi monkey alarm calls

Black-fronted titi monkeys, Callicebus nigrifrons, produce acoustically distinct vocalizations in response to several predator species. Compared to other primates, the calls are remarkably quiet, high-pitched and structurally simple, suggesting that they may not function uniquely as predator-specific warning calls. To address this, we investigated whether conspecifics were able to respond to these calls in adaptive ways, by playing back call series originally given to a perched raptor (caracara) and terrestrial predatory mammals (oncilla and tayra). Monkeys responded strongly and in predator-specific ways. Specifically, listeners preferentially looked upwards when hearing raptor-related calls, and towards the presumed caller when hearing terrestrial predator-related calls. Locomotor responses were generally uncommon, but if they occurred then they were always in the expected direction. We concluded that black-fronted titi monkeys discriminated between calls given to different predators on the basis of their acoustic features and were able to make inferences about the type or likely location of the predator.