Résultat de la recherche
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.
Referential alarm calling behaviour in New World primates
There is relatively good evidence that non-human primates can communicate about objects and events in their environment in ways that allow recipients to draw inferences about the nature of the event experienced by the signaller. In some species, there is also evidence that the basic semantic units are not individual calls, but call sequences and the combinations generated by them. These two findings are relevant to theories pertaining to the origins of human language because of the resemblances of these phenomena with linguistic reference and syntactic organisation. Until recently, however, most research efforts on the primate origins of human language have involved Old World species with comparatively few systematic studies on New World monkeys, which has prevented insights into the deeper phylogenetic roots and evolutionary origins of language-relevant capacities. To address this, we review the older primate literature and very recent evidence for functionally referential communication and call combinations in New World primates. Within the existing literature there is ample evidence in both Callitrichids and Ce-bids for acoustically distinct call variants given to external disturbances that are accompanied by distinct behavioural responses. A general pattern is that one call type is typically produced in response to a wide range of general disturbances, often on the ground but also including inter-group encounters, while another call type is produced in response to a much narrower range of aerial threats. This pattern is already described for Old World monkeys and Prosimians, suggesting an early evolutionary origin. Second, recent work with black-fronted titi monkeys has produced evidence for different alarm call sequences consisting of acoustically distinct call types. These sequences appear to encode several aspects of the predation event simultaneously, notably predator type and location. Since meaningful call sequences have already been described in Old World primates, we suggest that basic combinatorial vocal communication has evolved in the primate lineage long before the advent of language. Moreover, it is possible that some of these communicative abilities have evolved even earlier, or independently, as there is comparable evidence in other taxonomic groups. We discuss these findings in an attempt to shed further light on the primate stock from which human language has arisen.
The alarm call system of wild black-fronted titi monkeys, Callicebus nigrifrons
Upon encountering predators, many animals produce specific vocalisations that alert others and sometimes dissuade the predators from hunting. Callicebus monkeys are known for their large vocal repertoire, but little is known about the function and meaning of most call types. We recorded a large number of natural predator responses from five different groups of black-fronted titi monkeys in their Atlantic forest habitat in South Eastern Brazil. When detecting predatory threats, adult group members responded with call sequences that initially consisted of two brief, high-pitched calls with distinct frequency contours. Call A was mainly given to raptors but also to predatory capuchin monkeys and other threats within the canopy, while call B was given to predatory or non-predatory disturbances on the ground. In later parts of the sequences, we also recorded a high-pitched unmodulated call C and various low-pitched loud calls. Results therefore suggest that calls A and B provide listeners with rapid and reliable information about the general classes of danger experienced by the caller, while obtaining more specific information through other call types and combinations and behavioural responses. We discuss these findings in relation to current evolutionary theory of primate communication.