Zuberbühler, Klaus

2016-5-1, Coye, Camille, Zuberbühler, Klaus, Lemasson, Alban

2014, Schlenker, Philippe, Chemla, Emmanuel, Arnold, Kate, Lemasson, Alban, Ouattara, Karim, Keenan, Sumir, Stephan, Claudia, Ryder, Robin, Zuberbühler, Klaus

We develop a formal semantic analysis of the alarm calls used by Campbell's monkeys in the Tai forest (Ivory Coast) and on Tiwai island (Sierra Leone)-two sites that differ in the main predators that the monkeys are exposed to (eagles on Tiwai vs. eagles and leopards in Tai). Building on data discussed in Ouattara et al. (PLoS ONE 4(11):e7808, 2009a; PNAS 106(51): 22026-22031, 2009b and Arnold et al. (Population differences in wild Campbell's monkeys alarm call use, 2013), we argue that on both sites alarm calls include the roots krak and hok, which can optionally be affixed with -oo, a kind of attenuating suffix; in addition, sentences can start with boom boom, which indicates that the context is not one of predation. In line with Arnold et al., we show that the meaning of the roots is not quite the same in Tai and on Tiwai: krak often functions as a leopard alarm call in Tai, but as a general alarm call on Tiwai. We develop models based on a compositional semantics in which concatenation is interpreted as conjunction, roots have lexical meanings, -oo is an attenuating suffix, and an all-purpose alarm parameter is raised with each individual call. The first model accounts for the difference between Tai and Tiwai by way of different lexical entries for krak. The second model gives the same underspecified entry to krak in both locations (= general alarm call), but it makes use of a competition mechanism akin to scalar implicatures. In Tai, strengthening yields a meaning equivalent to non-aerial dangerous predator and turns out to single out leopards. On Tiwai, strengthening yields a nearly contradictory meaning due to the absence of ground predators, and only the unstrengthened meaning is used.

2011, Lemasson, Alban, Hausberger, Martine, Zuberbühler, Klaus

, Candiotti, Agnès, Zuberbühler, Klaus, Lemasson, Alban

Non-human primates possess species-specific repertoires of acoustically distinct call types that can be found in adults in predictable ways. Evidence for vocal flexibility is generally rare and typically restricted to acoustic variants within the main call types or sequential production of multiple calls. So far, evidence for context-specific call sequences has been mainly in relation to external disturbances, particularly predation. In this study, we investigated extensively the vocal behaviour of free-ranging and individually identified Diana monkeys in non-predatory contexts. We found that adult females produced four vocal structures alone (‘H’, ‘L’, ‘R’ and ‘A’ calls, the latter consisting of two subtypes) or combined in non-random ways (‘HA’, ‘LA’ and ‘RA’ call combinations) in relation to ongoing behaviour or external events. Specifically, the concatenation of an introductory call with the most frequently emitted and contextually neutral ‘A’ call seems to function as a contextual refiner of this potential individual identifier. Our results demonstrate that some non-human primates are able to increase the effective size of their small vocal repertoire not only by varying the acoustic structure of basic call types but also by combining them into more complex structures. We have demonstrated this phenomenon for a category of vocalisations with a purely social function and discuss the implications of these findings for evolutionary theories of primate vocal communication.

2015, Coye, Camille, Zuberbühler, Klaus, Lemasson, Alban

2013, Keenan, Sumir, Lemasson, Alban, Zuberbühler, Klaus

A standard way of describing the vocal behaviour of nonhuman primates is to classify the vocal repertoire as either graded or discrete. We analysed a large database of calls given by adult males of a primate considered a typical example for discrete vocal behaviour, the forest-dwelling Campbell's monkeys, Cercopithecus campbelli. We recorded vocal responses from several dozen individuals to their main predators, crowned eagles and leopards. Using cluster analysis techniques, we found two main call types, which were modified further by optional affixation of an inflexible vocal structure. It was possible to force the four call types into eight subtypes, with various degrees of gradedness. When taking context into account, we found that acoustically discrete and nonaffixed calls tended to be given right after discovering a predator, while acoustically graded and affixed calls were given during later parts of a predator encounter and to nonpredatory disturbances. In sum, our results suggest that classifications of primate vocal repertoires as either discrete or graded are likely to be meaningless, as communicatively relevant acoustic variation can be present within seemingly discrete call types. Crown Copyright (C) 2012 Published on behalf of The Association for the Study of Animal Behaviour by Elsevier Ltd. All rights reserved.

, Candiotti, Agnès, Zuberbühler, Klaus, Lemasson, Alban

Individually distinct vocalizations are widespread among social animals, presumably caused by variation in vocal tract anatomy. A less-explored source of individual variation is due to learned movement patterns of the vocal tract, which can lead to vocal convergence or divergence in social groups. We studied patterns of acoustic similarity in a social call produced by 14 female Diana monkeys (Cercopithecus diana) in two free-ranging groups. Calls showed variability in fundamental frequency contours owing to individual identity and external context. Vocal divergence increased significantly between females during poor visibility and tended to increase in the presence of neighbours. In contrast, vocal convergence increased significantly between females during vocal interactions, because females matched the frequency contour of their own call with another females preceding call. Our findings demonstrate that these primates have some control over the acoustic fine structure of their most important social vocalization. Vocal convergence and divergence are two opposing processes that enable callers to ensure spatial proximity and social cohesion with other group members.

2015, Coye, Camille, Ouattara, Karim, Zuberbühler, Klaus, Lemasson, Alban

Compared to humans, non-human primates have very little control over their vocal production. Nonetheless, some primates produce various call combinations, which may partially offset their lack of acoustic flexibility. A relevant example is male Campbell's monkeys (Cercopithecus campbelli), which give one call type ('Krak') to leopards, while the suffixed version of the same call stem ('Krak-oo') is given to unspecific danger. To test whether recipients attend to this suffixation pattern, we carried out a playback experiment inwhichwe broadcast naturally and artificially modified suffixed and unsuffixed 'Krak' calls of male Campbell's monkeys to 42 wild groups of Diana monkeys (Cercopithecus diana diana). The two species form mixed-species groups and respond to each other's vocalizations. We analysed the vocal response of male and female Diana monkeys and overall found significantly stronger vocal responses to unsuffixed (leopard) than suffixed (unspecific danger) calls. Although the acoustic structure of the 'Krak' stem of the calls has some additional effects, subject responses were mainly determined by the presence or the absence of the suffix. This study indicates that suffixation is an evolved function in primate communication in contexts where adaptive responses are particularly important.

2013, Candiotti, Agnes, Zuberbühler, Klaus, Lemasson, Alban

One accepted function of vocalisations is to convey information about the signaller, such as its age-sex class, motivation, or relationship with the recipient. Yet, in natural habitats individuals not only interact with conspecifics but also with members of other species. This is well documented for African forest monkeys, which form semi-permanent mixed-species groups that can persist for decades. Although members of such groups interact with each other on a daily basis, both physically and vocally, it is currently unknown whether they can discriminate familiar and unfamiliar voices of heterospecific group members. We addressed this question with playbacks on monkey species known to form polyspecific associations in the wild: red-capped mangabeys, Campbell's monkeys and Guereza colobus monkeys. We tested subjects' discrimination abilities of contact calls of familiar and unfamiliar female De Brazza monkeys. When pooling all species, subjects looked more often towards the speaker when hearing contact calls of unfamiliar than familiar callers. When testing De Brazza monkeys with their own calls, we found the same effect with the longest gaze durations after hearing unfamiliar voices. This suggests that primates can discriminate, not only between familiar and unfamiliar voices of conspecifics, but also between familiar and unfamiliar voices of heterospecifics living within a close proximity. (C) 2013 Elsevier B.V. All rights reserved.

, Ouattara, Karim, Lemasson, Alban, Zuberbühler, Klaus

Habitat type, predation pressure and reproductive interests are all thought to determine the anti-predator behaviour of non-primates, but only few systematic studies exist. Here, we experimentally elicited anti-predator behaviour in six different groups of forest-living Campbell’s monkeys, using visual and acoustic models of leopards, crowned eagles, and snakes. Individuals produced a variety of anti-predator behaviours, depending on the type of predator and whether or not it was visible. Adult males generally behaved conspicuously, either by attacking eagles or producing threat behaviours at a distance to leopards. Adult females remained cryptic to eagles, but joined their male in approaching leopards. To snakes, both males and females responded strongly to familiar Gaboon vipers, but far less to unfamiliar black mambas. Finally, if a predator could only be heard, both males and females produced fewer alarm calls and often changed their vertical position in the canopy (upwards for leopards; downwards for eagles), despite all predator vocalisations being presented from the ground. We concluded that Campbell’s monkeys display sex-specific anti- predator behaviours, which are largely driven by the predators’ hunting techniques, mode of predator detection and the forest habitat structure.