On the -oo ‘suffix’ of Campbell’s monkeys (C. campbelli)

Résumé En

Ouattara et al. (2009a,b) make the novel claim that Campbell’s monkey alarm calls demonstrate a simple pattern of linguistic morphology. The authors observe that there are at least two distinct alarm calls (called krak and hok) that are used in two different predatory contexts, and that each may be followed by a low frequency sound (called -oo) that alters the meaning of both calls in predictable ways, allowing contexts with reduced level of threat. In light of these facts, -oo is analyzed as a meaning-bearing, combinatorial unit. However, the claim that a non-human communication system has a combinatorial system (however primitive) is rare in the literature (see x5 for related patterns), and, indeed, is antithetical to certain claims that structural hierarchy is unique to human language (e.g., Bolhuis et al. 2014). Moreover, it has been noted (Schlenker et al. 2014) that there is redundancy between the apparent semantic contribution of -oo and the semantic contribution of a variety of other signal manipulations (e.g. calling rate) that are easiest to explain via non-compositional mechanisms. These facts warrant particular caution when evaluating the pattern as a possible counterexample to generalizations about human language. Thus, in this squib, we examine the compositional hypothesis further. As counterpoint, we consider a class of more conservative hypotheses in which -oo does not itself bear meaning, but instead arises as the side effect of other articulatory processes that noncompositionally affect call meaning. Key to such hypotheses is the premise that -oo is articulatorily parasitic on another phonetic process. A major contribution of this squib is thus phonetic: considering the acoustic properties of -oo, we conclude that complex calls (krakoo and hokoo) are produced with a two pulses of a single breath-group. Critically, the production of these complex calls requires an additional articulatory gesture and thus an increase in articulatory effort. An increase in articulatory effort would not be expected on an analysis in which -oo arises as a phonetic side effect; we accordingly reject these alternate hypotheses, thus strengthening the robustness of the combinatorial analysis.