Communication Network Reflects Social Instability in a Wild Siamang (Symphalangus syndactylus) Population

Long-range signaling, such as acoustic communication, is best understood within the broader context of all potential receivers. Exactly what kind of information is transmitted or obtained is a matter of debate. To address this issue, we describe the communication network of a population of wild siamangs (Symphalangus syndactylus), small territorial apes that sing loud and complex duets. Based on calling data collected over >3400 observation hours on 7 groups of wild siamangs, we used linear mixed-effects models to evaluate the effect of changes in group composition on singing rates and social network analysis to study the effect of social change on the structure of this siamang communication network. Results show that, compared to stable groups, groups whose composition had recently changed elicited significantly more responses to their calls from neighboring groups. These results support the hypothesis that listening individuals can take advantage of public information to detect points of social instability in the community, e.g., adult males seeking opportunities to obtain their own territory. Our results help explain some sociobiological conundrums concerning hylobatids, e.g., by highlighting a potential strategic benefit for males living in the multimale, single female groups that are reported in some species, advance our understanding of the function of calling in hylobatids, and offer theoretical and methodological insights applicable to other taxa such as birds and cetaceans.

Automated summary

Research on wild siamangs demonstrates that changes in group composition can affect calling rates and communication network structure, possibly because listening individuals utilize public information to detect social instability. These findings help explain some sociobiological conundrums surrounding siamangs and offer insights applicable to other taxa such as birds and cetaceans.