Anthropogenic noise is a global pollutant known to affect the behaviour of individual animals in all taxa studied. However, there has been relatively little experimental testing of the effects of additional noise on social interactions between conspecifics, despite these forming a crucial aspect of daily life for most species. Here we use established paradigms to investigate how white-noise playback affects both group defensive actions against an intruder and associated within-group behaviours in a model fish species, the cooperatively breeding cichlid Neolamprologus pulcher. Additional noise did not alter defensive behaviour, but did result in changes to within-group behaviour. Both dominant and subordinate females, but not the dominant male, exhibited less affiliation and showed a tendency to produce more submissive displays to groupmates when there was additional noise compared to control conditions. Our experimental results therefore indicate the potential for anthropogenic noise to affect social interactions between conspecifics and that there can be intraspecific variation in the impacts of this global pollutant.

To investigate the influence of additional noise on territory defence and associated within-group behaviour, we gave 16 groups of daffodil cichlids (Neolamprologus pulcher) two treatments each in a repeated-measures design: during the simulated territorial intrusion of a rival female, there was playback of either white noise (additional noise) or silence (loudspeaker turned on but not playing any sound, as a control). We video-recorded all trials and scored behaviours using the ethogram from Braga Goncalves et al,. 2020. For each 10-min intrusion period, we scored defensive behaviours for each category of individual (DM, DF, SF) and the total amount received by the intruder. We also scored all affiliation and aggression displayed to other group members by each category of individual during the intrusion period. We examined the effect of additional noise on the total defensive effort against the intruder; we then determined whether the non-significant treatment difference was consistent across all three individual categories or if there were counterbalancing effects between group members. Second, we investigated the effect of additional noise on the overall amount of within-group aggression, affiliation and submission exhibited; we used the sequential Bonferroni correction as there was a separate test for each behaviour. For those behaviours found to be significantly different between treatments (affiliation and submission; see Results), we determined which group members were driving the differences.

Spreadsheet of study results includes four excel tabs, corresponding to each of the main elements of the manuscript: defensive actions against intruders, within-group affiliation displayed, within-group aggression displayed, and within-group submission displayed. DF = dominant female, DM = dominant male, S = subordinate.