Emotional contexts influence vocal individuality in ungulates

To group-living animals, such as most ungulates, being able to recognise the members of one’s social groups is crucial. While vocalisations often carry cues to identity, they are also impacted by the affective state of the caller, with signals often becoming more chaotic in contexts of negative valence or high arousal. How might this influence vocal individuality – and is there a pattern across taxa? To understand how the individual information content is maintained over emotionally charged contexts, we studied putatively negative and positive contact calls of seven ungulate species: cattle, goats, sheep, pigs, wild boars, horses, and Przewalski’s horses. The information content of these calls was assessed using Beecher’s statistic and the Potential of Individuality Coding. Across the species, the information content was lower in calls of negative than positive valence. In each of the species, at least one acoustic parameter was a reliable indicator of individuality across contexts. Our results indicate that negative valence overrides individual information in ungulate vocalisations at least to some extent, and imply that individual vocal recognition may require acoustic stability of certain important parameters. These findings reveal a nuanced role of affective communication in maintaining social bonds among socially complex animals.