Abstracts

Zanna Clay: "Production and understanding of meaningful call combinations in bonobos (Pan paniscus)"

Bonobos (Pan paniscus) are still one of the least well understood of the great apes, especially compared to their better known cousins, the chimpanzees (Pan troglodytes). This is especially evident in the domain of communication, with bonobo vocal behaviour a neglected field of study. Here, I address this by presenting a series of studies examining natural vocal communication in bonobos, focusing principally on the manner in which bonobos combine different calls together to create call sequences that convey information about something in the external world. Using a combination of observational and experimental techniques, we have shown that bonobos both produce and understand vocal sequences that convey meaningful information about food quality, which receivers then use to guide foraging decisions. Overall, I will discuss the relevance of studying primate vocalisations for investigating the evolution of language and linguistic properties such as syntax and semanticity.

James L. Fuller: "Differentiating and reconciling function and “meaning” – signal content in the loud calls of adult male blue monkeys (Cercopithecus mitis)."

Animal communication researchers frequently seek to identify “information” in signals as a way of explaining receiver responses and to assign signals to functional classes (e.g. predator alarm calls). Though the concept is appealing, primarily due to intuitive similarities to its use in human language, the applicability of “information” to non-human signaling has been criticized as poorly defined and possibly inappropriate to study of animal communication. Consistent associations between features of signals (e.g. acoustic structure, patterns of use) and attributes of signalers (e.g. sex, body size, attention to predators) can, however, provide an objective, quantitative metric to explain receiver response in an evolutionary context. Such associations (for which I use the label “signal content”) are critical to understanding function (sensu Tinbergen) of signals, but avoid presuming or implying proximate mechanisms for the observed responses. I report on data from a long term study of vocal communication in wild blue monkeys (Cercopithecus mitis). Results from natural observations and playback experiments show that adult male “loud calls” – audible to conspecifics at distances up to a kilometer away – evoke behavioral responses that differ consistently based on the age-sex class and social status of receivers, and thus simultaneously achieve multiple intra- and intergroup functions. I will discuss these results in relation to multiple features of signal content identified in each call and how these findings might influence characterization of what signals “mean”.

Jean-Pierre Gautier: "Structures and Functions of the Vocalizations of primates of Central African forest – A Retrospective"

The optical density of tropical forest led animals which have evolved within this environment to develop particular communication modes. Visually, species display striking colorations of their fur or masks, linked with their specific identification or dissimulation effect for their potential predators. Acoustic exchanges are their major communication mode. For the observer, vocalizations are the most obvious behavior, while it remains difficult to got access to their other behaviors. These difficulties increase for arboreal monkeys, in hunting areas. These conditions mainly drive our research towards: i) comparative studies of vocal behavior, for six species of cercopithecines and one of mangabey, later extended to other species ; ii) The synecological studies of the different species which mainly live in polyspecific troops; iii) The need to constitute a captive colony to undertake more precise observations of behavior.

The main motivation of acoustic studies was to discover an eventual link with our own language. This latter vanished, as soon as we were convinced that the sounds of monkeys were genetically determined. Young monkeys possess all the repertoire of their own species, excepted those linked with sexual maturity. Moreover they are unable to imitate some sounds of other species.

We will report here the major discoveries of our studies. The first step was to establish the vocal repertoire of the different species. Two categories of repertoires will be distinguished. The common one, constituted by the vocalizations given by all individuals of the social group, and the exceptional one, constituted by loud calls only given by adult males and social leaders. We will focus on these Loud calls. After their specific description, we will describe: their expression modalities and their contextual situations of production, leading to discover their proximal functions; the laryngeal mechanisms of their production, allowing their power and their low pitch; the ontogenetic phenomenon leading to the vocal breaking of the voice of adult males after their sexual maturity, and the discovery of totally new vocal types linked with their social leadership. Finally, we will tentatively give their ultimate function, linked to the intergroup spacing and the specific reproductive isolation.

Émilie Genty: "Multi-modal use of a socially directed call in bonobos: the 'contest hoots'"

Human language is fundamentally multi-modal and speech is usually associated with gestures and other visual cues to convey an overall meaning. An important question is whether there is an evolutionary older primate origin of multi-modal communication? The aim of this study was to describe the multi-modal use of 'contest hoots', a vocalization produced by male bonobos. We found that contest hooting, with or without other associated signals, was produced to challenge and provoke a social reaction in the targeted individual, usually agonistic chase. Interestingly, ‘contest hoots’ were sometimes also used during friendly play. In both contexts, males were highly selective in whom they targeted by preferentially choosing individuals of equal or higher social rank, suggesting that the calls functioned to assert social status. Multi-modal sequences were not more successful in eliciting reactions than contest hoots given alone, but we found a significant difference in the choice of associated gestures between playful and agonistic contexts. During friendly play, contest hoots were significantly more often combined with soft than rough gestures compared to agonistic challenges, while the calls’ acoustic structure remained the same. We conclude that contest hoots indicate the signaller’s intention to interact socially with important group members, while the gestures provide additional cues concerning the nature of the desired interaction.

Mary Glenn and Keith Bensen: "Intraspecific Comparisons of Cercopithecus Mona Vocalizations in Native and Introduced Ranges with an Emphasis on Copulation and Male Loud Calls"

The unique geographic distribution and natural history of the mona monkey (Cercopithecus mona) have allowed us to compare the influence of widely varying ecological conditions and artificial selection pressure. Mona monkeys live a in a broad range of forest types. In their native range of eastern Ghana to western Cameroon, mona monkeys coexist with a wide variety of primate species, while in their introduced island ranges of São Tomé and Príncipe and Grenada (where they have existed in isolation for at least 250 years), they are the only extant primate species. The Grenada population, now numbering in the thousands, has gone through extreme serial genetic bottlenecks. Across monas’ native and introduced ranges, no calls have been added or deleted from any population’s repertoire, and the basic behavioral function of all calls appears to be uniform across their native and introduced ranges.

Mona monkeys, unlike most guenons and most primates in general, emit gender specific calls during copulation. The distinctiveness of the gender specific calls suggests that a primary function of the mona copulation call may be to increase female reproductive success. Mona male loud calls vary in structure across their range. We compared the loud calls from tropical dry forests in Benin to populations in Cameroon and Grenada that occupy denser and wetter forests. The booms of the three populations varied, with Grenada averaging the most narrow bandwidth (145-215 Hz) and shortest duration (90 ms) (n=16). Cameroon loud calls (n=19) were distinguished from both Grenada and Benin loud calls (n=16) in having a broader average bandwidth (97-389 Hz) and longer duration (144 ms). Interestingly, the bandwidth of mona loud calls from Cameroon closely resembles the loud calls of sympatric Cercopithecus pogonias; however, the latter emits only single phrase loud calls, whereas monas tend to have double phrase loud calls. The loud calls of Grenada monas may be affected by genetic drift or ecological release. The similarities between C. mona and C. pogonias loud calls in Cameroon may be partially explained by similar acoustic environmental pressures or by the benefits of interspecies communication in two species that are known to hybridize.

Alban Lemasson: "Socially-guided vocal flexibility in nonhuman primates"

While most authors believe that it is legitimate to argue in favor of a coevolution between sociality and communicative complexity in vertebrates, the vocal repertoires of monkeys and apes, living in complex social systems, have traditionally been described as very rigid, compared to birds or cetaceans for instance. However, recent evidences of vocal flexibility under social influences have been provided in a growing number of nonhuman primate species. First, while the species call type repertoire is mainly genetically determined, juvenile and adult individual call structures are far more plastic than previously thought. Second, when investigating individual vocal repertoires using a multi-level approach (i.e. sound unit, call type, vocal sequence) a flexible organization which enables a complex acoustic encoding of information is revealed. Third, the analysis of the social context and organization of vocal interactions at a multi-individual level demonstrates another dimension of vocal flexibility in both juveniles and adults. All those recent findings converge towards the idea that vocal flexibility in nonhuman primates has been largely underestimated so far. More comparative studies are now needed to understand the evolution of acoustic plasticity and communicative abilities in the primate lineage.

Philippe Schlenker: "Formal Monkey Linguistics"

based on joint work with Emmanuel Chemla, Cristine Cäsar, Kate Arnold, Sumir Keenan, Karim Ouattara, Jeremy Kuhn, Alban Lemasson, Anne Schel, Robin Ryder, Klaus Zuberbühler

We argue that rich data gathered in experimental primatology in the last 40 years might benefit from the type of analytical methods used in contemporary linguistics (from this methodological proposal, no claim follows about an evolutionary connection between primate calls and human language – a question we set aside here). Focusing on the syntactic and especially semantic side, we argue that these methods could help clarify five questions: (i) what syntax, if any, do monkey calls have? (ii) what is the 'lexical meaning' or proximate trigger of individual calls? (iii) how are the meanings of individual calls combined? (iv) how do calls or call sequences compete with each other when several are appropriate in a given situation? (v) what is the division of labor between call meanings and world knowledge in information transmission? We illustrate the benefits of this 'monkey linguistics' by way of cases studies in which we seek to assess the merits of competing theories.

In Schlenker et al. 2014, we investigated the alarm calls of male Campbell's monkeys from two sites, the Tai forest (main predators: leopards and eagles) and Tiwai island (main predators: eagles – and no leopards). Three features of the analysis are particularly relevant. First, a suffix, -oo, was taken to modify in a regular way the meaning of two roots (krak and hok), hence a non-trivial compositional structure at the word level. Second, there was evidence for apparent 'dialectal' variation: one of the calls, krak, was primarily used as a leopard alarm in Tai, but as a general alarm on Tiwai. Third, while one possible analysis posits a difference in the lexical meaning of krak across Tai and Tiwai, a possibly superior alternative posits a uniform meaning of general alarm at the two sites, together with a process of pragmatic enrichment akin to scalar implicatures: the competition between krak (≈ alarm) and (i) krak-oo (≈ weak alarm) and (ii) hok (≈ aerial threat) leads to an enriched meaning of 'serious ground alarm' in Tai, hence a predominant leopard use; on Tiwai, the same enrichment process leas to a nearly useless meaning for lack of ground predators, hence the enrichment operation isn't applied and the unadorned lexical meaning is seen.

One important weakness of Schlenker et al. 2014 was that the Campbell's data did not allow for clear syntactic generalizations, and hence no complete 'monkey fragment' could be defined. In ongoing work, we revisit two species whose calls display a much more manageable syntax, as well as interesting questions of semantic interpretation.

–Putty-nosed monkeys have two main calls, pyows, which have a general meaning, and hacks, which often have an eagle alarm function. They are arranged in four kinds of sequences: pure pyow sequences; pure hack sequences; series of hacks followed by series of pyows (= 'transitional sequences'); and a small number of pyows followed by a small number of hacks (= 'pyow-hack sequences'). The main puzzle, discussed recently by Arnold and Zuberbühler 2012, is that pyow-hack sequences are predictive of group movement, although it is not clear how this function can be derived from the individual meanings of the calls. Arnold and Zuberbühler conclude that this is a case of syntactic combination without semantic composition, and propose that pyow-hack sequences have a kind of idiomatic meaning. We explore an alternative in which calls have an underspecified meaning, which is enriched not just by way of competition with other calls (as in our analysis of Campbell's semantics), but also by an 'Urgency Principle' which mandates that calls that are indicative of predators should come at the beginning of sequences; this turns out to derive the use of pyow-hack sequences without positing 'idiomatic' meanings.

–Titi monkey calls (Cäsar et al. 2012, 2013) are remarkable in that they give rise to relatively stable stereotyped sequences of calls, which were shown in controlled field experiments to convey information both about predator type (e.g. cat vs. eagle) and predator position (on the ground vs. in trees). While these results might initially suggest that Titi monkeys have a sophisticated proto-language with a complex syntax/semantics interface, we will argue instead that the basic calls have very simple meanings (subject to some rules of pragmatic competition); and that the richness of the calling patterns is largely due to the interaction between independently motivated ecological conditions and these very simple meanings.

In sum, our Campbell's data highlight the importance of competition among calls to obtain enrichments akin to scalar implicatures; Putty-nosed data show that further pragmatic rules (our 'Urgency Principle') can be crucial as well; and Titi data suggest that complex syntactic patterns may correlate with rich environmental conditions without thereby encoding information about the latter at a semantic level.

Background reading: Schlenker et al. 2014, 'Monkey Semantics: Two 'Dialects' of Campbell's Monkey Alarm Calls', to appear in Linguistics & Philosophy; available at http://ling.auf.net/lingbuzz/001792