White-handed gibbons discriminate context-specific song compositions

Abstract

White-handed gibbons produce loud and acoustically complex songs when interacting with their neighbours or when encountering predators. In both contexts, songs are assembled from a small number of units although their composition differs in context-specific ways. Here, we investigated whether wild gibbons could infer the ‘meaning’ when hearing exemplars recorded in both contexts (i.e. ‘duet songs’ vs. ‘predator songs’). We carried out a playback experiment by which we simulated the presence of a neighbouring group producing either its duet or a predator song in order to compare subjects’ vocal and locomotor responses. When hearing a recording of a duet song, subjects reliably responded with their own duet song, which sometimes elicited further duet songs in adjacent groups. When hearing a recording of a predator song, however, subjects typically remained silent, apart from one of six groups which replied with its own predator song. Moreover, in two of six trials, playbacks of predator songs elicited predator song replies in non-adjacent groups. Finally, all groups showed strong anti-predator behaviour to predator songs but never to duet songs. We concluded that white-handed gibbons discriminated between the two song types and were able to infer meaning from them. We discuss the implications of these findings in light of the current debate on the evolutionary origins of syntax.

Syntax and compositionality in animal communication

“…White-handed gibbons, however, also sing to predators, notably tigers, clouded leopards and pythons, with predator songs and duet songs assembled in different ways [27]. Naturalistic observations [27] and playback experiments [28] suggest that recipients discriminate predator and non-predator songs by showing appropriate behavioural responses. But as individual song units are meaningless, gibbon song does not technically qualify as syntax either.…”

Adherence to Menzerath's Law is the exception (not the rule) in three duetting primate species

“…Non-human primate duets tend to follow a stereotyped pattern, but there is evidence that duets emitted under different contexts (e.g. during inter-group encounters or in the presence of predators [ 39 ]) have a slightly different structure, and that conspecifics respond differently to duets emitted under different contexts [ 40 ]. In addition, certain features of primate long calls contain information about caller condition or quality.…”

The biological roots of music and dance: Extending the credible signaling hypothesis to predator deterrence

“…White-handed gibbons also sing predator-specific songs in response to tigers and leopards, ambush predators, but not other predators (Clarke, Reichard, & Zuberbühler, 2006. Although these songs clearly serve as alarm calls to other gibbons, they also function to deter predators, perhaps by advertising to ambush predators that they have been detected (Andrieu et al, 2020).…”

“…In white-handed gibbons, for instance, duet songs, which serve territorial defense and other functions, are similar to predator songs, which are sung when a predator is detected. Nevertheless, gibbons readily discriminate between the two songs, engaging in vigilance behaviors following predator songs but never following duet songs (Andrieu et al, 2020).…”