Social vocalizations indicate behavioural type in Glossophagine bats

Abstract

Vocalizations play a crucial role in the social systems of many animals and may inadvertently reveal behavioural characteristics of the sender. Bats, the second largest mammalian order, rely extensively on vocalizations owing to their nocturnal lifestyle and complex social systems, making them ideal for studying links between vocalizations and consistent behavioural traits. In this study, we developed a new testing regime to investigate whether consistent individual vocalization differences in nectarivorous bats are associated with specific behavioural types. We exposed 60 wild, male Glossophaga soricina handleyi bats to novel and risky stressors and assessed their behavioural and vocal responses. Proactive, exploratory and bold bats were more likely to produce social calls, and among the vocalizing bats, more agitated bats produced higher numbers of social calls. We thus show that bat vocalization behaviour can be indicative of a certain behavioural type, potentially allowing conspecifics to assess personalities from a distance, which in turn could impact subsequent social interactions, group dynamics and reproductive success. Our results, in combination with previous findings in birds, suggest that advertent or inadvertent long-distance broadcasting of personality may be widespread, thus opening up new exciting questions about the links between vocalizations and sociality.

Keywords: Glossophaga bats; animal personality; behavioural syndrome; communication; consistent between-individual differences; vocalizations.

Figure 1.

Alert calls and their prevalence among G. s. handleyi. (A) Oscillogram (upper panel) and spectrogram (central panel) images of an alert call, showing time on the x-axis and voltage and frequency on the y-axis, respectively. The left panel depicts the power spectrum of the call, with intensity on the x-axis and frequency on the y-axis. (B) Call activity among all bats in all trials (N = 330). (C) Density and histogram plot showing the distribution of the number of social calls among the vocally active bats. Turquoise bars and line show the number of calls during the first trial, while grey bars and black line depict the second trial.

Figure 2.

Scatterplots showing Pearson’s correlations between PC1s from different tests (N = 43). Dots depict single individuals, shaded areas around the trendlines show the 95% CI. (A) Strong positive correlation between Reactiveness–Proactiveness (NE test) and Avoidance–Exploration (NO test). (B) Strong positive correlation between Shyness–Boldness (FUR test) and Avoidance–Exploration (NO test).

Figure 3.

3D system of coordinates representing three major personality axes: Reactiveness–Proactiveness, Avoidance–Exploration and Shyness–Boldness derived from the first principal components of the NE, NO and FUR test, respectively. Negative values indicate higher levels of Reactiveness, Avoidance and Shyness, while positive values refer to higher levels of Proactiveness, Exploration and Boldness, respectively. Each bat is represented as an individually coloured dot, while dot size depicts the number of social calls produced (bigger dots indicate a higher numbers of social calls).

Figure 4.

Violin plots depicting the mean number of (A) object inspections during cNO and NO (N = 46) and (B) feeding events during cFUR and FUR (N = 52). The numbers of object inspections and feeding events were averaged per individual across trials. The white, whiskered dots inside the violins depict the mean and 95% CIs. p-values of the Wilcoxon signed rank test are displayed in each panel for the respective test.