Context-dependent variation in meerkat short note calls reflects emotional arousal

Many animals produce the same call type in distinct contexts, yet acoustic variation can encode additional information, such as the producers' emotional state. By doing so, animals increase their capacity to communicate within potentially limited vocal repertoires. Meerkats, Suricata suricatta, produce various types of short note calls during distinct behavioural contexts; sunning, i.e. basking in the sun, and sentinel, i.e. cooperative vigilance. These two contexts likely vary in underlying emotional arousal. We first investigated if heart rate differed between sunning and sentinel contexts, indicating potential variation in arousal states. Second, we tested if calls produced during sunning and sentinel vary in production rate, call type and acoustic structure. We implanted wild meerkats with heart rate loggers and recorded their behaviour and vocalisations. We found that sentinel behaviour was associated with higher heart rates and call rates, indicating increased affective arousal. The acoustic structure of calls produced during sentinel were consistent with predictions of increased arousal, compared to calls produced during sunning, showing increased jitter, shorter duration, and more abrupt in onset. Overall, our results suggest higher emotional arousal during sentinel behaviour than sunning, reflected in cardiac activity, call rate and acoustic variation. Our results highlight that even within short, seemingly simple vocalisations, acoustic variation can enhance the amount of information transferred.