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Context-specific close-range "hoo" calls in wild gibbons (Hylobates lar).

Clarke E, Reichard UH, Zuberbühler K - BMC Evol. Biol. (2015)

Bottom Line: Our study provides evidence that lar gibbons are able to generate significant, context-dependent acoustic variation within their main social call, which potentially allows recipients to make inferences about the external events experienced by the caller.Communicating about different events by producing subtle acoustic variation within some call types appears to be a general feature of primate communication, which can increase the expressive power of vocal signals within the constraints of limited vocal tract flexibility that is typical for all non-human primates.In this sense, this study is of direct relevance for the on-going debate about the nature and origins of vocally-based referential communication and the evolution of human speech.

View Article: PubMed Central - PubMed

Affiliation: Evolutionary Anthropology Research Group, Dawson Building, Durham University, Durham, DH1 3LE, UK. e.a.clarke@durham.ac.uk.

ABSTRACT

Background: Close range calls are produced by many animals during intra-specific interactions, such as during home range defence, playing, begging for food, and directing others. In this study, we investigated the most common close range vocalisation of lar gibbons (Hylobates lar), the 'hoo' call. Gibbons and siamangs (family Hylobatidae) are known for their conspicuous and elaborate songs, while quieter, close range vocalisations have received almost no empirical attention, perhaps due to the difficult observation conditions in their natural forest habitats.

Results: We found that 'hoo' calls were emitted by both sexes in a variety of contexts, including feeding, separation from group members, encountering predators, interacting with neighbours, or as part of duet songs by the mated pair. Acoustic analyses revealed that 'hoo' calls varied in a number of spectral parameters as a function of the different contexts. Males' and females' 'hoo' calls showed similar variation in these context-specific parameter differences, although there were also consistent sex differences in frequency across contexts.

Conclusions: Our study provides evidence that lar gibbons are able to generate significant, context-dependent acoustic variation within their main social call, which potentially allows recipients to make inferences about the external events experienced by the caller. Communicating about different events by producing subtle acoustic variation within some call types appears to be a general feature of primate communication, which can increase the expressive power of vocal signals within the constraints of limited vocal tract flexibility that is typical for all non-human primates. In this sense, this study is of direct relevance for the on-going debate about the nature and origins of vocally-based referential communication and the evolution of human speech.

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Related in: MedlinePlus

Two scatter plots of functions 1 (intercall interval) and 2 (low frequency/delta frequency) as they explain the variation between the different hoo contexts in males (M) and females (F). ○ = big cat; □ = raptor; ● = group encounter ∆ = duet; ■ = group centroid.
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Fig2: Two scatter plots of functions 1 (intercall interval) and 2 (low frequency/delta frequency) as they explain the variation between the different hoo contexts in males (M) and females (F). ○ = big cat; □ = raptor; ● = group encounter ∆ = duet; ■ = group centroid.

Mentions: We then conducted a step-wise discriminant function analysis, entering the five most readily measurable acoustic parameters (peak frequency, low frequency, delta frequency, duration and inter-call interval) to determine whether the different contexts could be separated by the interactions between the measured variables. Since sex differences were frequency-related we conducted separate DFAs for males and females. Also, since hoos to leopard and tiger models did not differ from each other, these were pooled as “big cat” responses. Sample sizes for feeding hoos proved to be too small for the DFA when we split males and females. Similarly, intensity was excluded because sample sizes became too low (<20) when this variable was entered and sexes were split. Interestingly, intensity strongly predicted hoo context in initial analyses, making it particularly relevant for future study. The DFA results are summarised in Tables 3 and 4 and Figure 2.Table 4


Context-specific close-range "hoo" calls in wild gibbons (Hylobates lar).

Clarke E, Reichard UH, Zuberbühler K - BMC Evol. Biol. (2015)

Two scatter plots of functions 1 (intercall interval) and 2 (low frequency/delta frequency) as they explain the variation between the different hoo contexts in males (M) and females (F). ○ = big cat; □ = raptor; ● = group encounter ∆ = duet; ■ = group centroid.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4389582&req=5

Fig2: Two scatter plots of functions 1 (intercall interval) and 2 (low frequency/delta frequency) as they explain the variation between the different hoo contexts in males (M) and females (F). ○ = big cat; □ = raptor; ● = group encounter ∆ = duet; ■ = group centroid.
Mentions: We then conducted a step-wise discriminant function analysis, entering the five most readily measurable acoustic parameters (peak frequency, low frequency, delta frequency, duration and inter-call interval) to determine whether the different contexts could be separated by the interactions between the measured variables. Since sex differences were frequency-related we conducted separate DFAs for males and females. Also, since hoos to leopard and tiger models did not differ from each other, these were pooled as “big cat” responses. Sample sizes for feeding hoos proved to be too small for the DFA when we split males and females. Similarly, intensity was excluded because sample sizes became too low (<20) when this variable was entered and sexes were split. Interestingly, intensity strongly predicted hoo context in initial analyses, making it particularly relevant for future study. The DFA results are summarised in Tables 3 and 4 and Figure 2.Table 4

Bottom Line: Our study provides evidence that lar gibbons are able to generate significant, context-dependent acoustic variation within their main social call, which potentially allows recipients to make inferences about the external events experienced by the caller.Communicating about different events by producing subtle acoustic variation within some call types appears to be a general feature of primate communication, which can increase the expressive power of vocal signals within the constraints of limited vocal tract flexibility that is typical for all non-human primates.In this sense, this study is of direct relevance for the on-going debate about the nature and origins of vocally-based referential communication and the evolution of human speech.

View Article: PubMed Central - PubMed

Affiliation: Evolutionary Anthropology Research Group, Dawson Building, Durham University, Durham, DH1 3LE, UK. e.a.clarke@durham.ac.uk.

ABSTRACT

Background: Close range calls are produced by many animals during intra-specific interactions, such as during home range defence, playing, begging for food, and directing others. In this study, we investigated the most common close range vocalisation of lar gibbons (Hylobates lar), the 'hoo' call. Gibbons and siamangs (family Hylobatidae) are known for their conspicuous and elaborate songs, while quieter, close range vocalisations have received almost no empirical attention, perhaps due to the difficult observation conditions in their natural forest habitats.

Results: We found that 'hoo' calls were emitted by both sexes in a variety of contexts, including feeding, separation from group members, encountering predators, interacting with neighbours, or as part of duet songs by the mated pair. Acoustic analyses revealed that 'hoo' calls varied in a number of spectral parameters as a function of the different contexts. Males' and females' 'hoo' calls showed similar variation in these context-specific parameter differences, although there were also consistent sex differences in frequency across contexts.

Conclusions: Our study provides evidence that lar gibbons are able to generate significant, context-dependent acoustic variation within their main social call, which potentially allows recipients to make inferences about the external events experienced by the caller. Communicating about different events by producing subtle acoustic variation within some call types appears to be a general feature of primate communication, which can increase the expressive power of vocal signals within the constraints of limited vocal tract flexibility that is typical for all non-human primates. In this sense, this study is of direct relevance for the on-going debate about the nature and origins of vocally-based referential communication and the evolution of human speech.

Show MeSH
Related in: MedlinePlus