It has been well established that mammals have evolved to efficiently regulate their heart rate with behaviors such as facial expression, listening, and vocalization. Heart rate can be promoted during fight or flight behaviors, or slowed to foster pro-social behaviors (we need to appear calm and cool so potential mates aren’t scared off). Among mammals, vocalizations are a key component of the conspecific communication system that can help individuals within the same species to signal environmental risks (predators). Given that the heart is controlled by the nervous system, a new study by Stewart et al. hypothesized that the muscles in the airway may also be affected during a physiological response (i.e. altered heart rate), leading to modulated vocalizations, such as higher pitch or frequency. To elucidate this effect, Prairie voles (Microtus ochrogaster) were used since they are very vocal and have a variable range in heart rate. By investigating both the pitch and variations in pitch within the frequency range used for social communication in the Prairie Vole, which occurs at about 20-40 kHz, they were able to observe an interaction between heart rate and vocalization.
It was found that heart rate was significantly correlated with fundamental frequency and duration. In other words, faster heart rates were associated with vocalizations characterized by a higher pitch and shorter duration. In humans, this state would be analogous to anxiety. The more nervous we are due to some environmental stressor, our sympathetic nervous system activates and increases heart rate. This in turn will tighten the muscles in our larynx and force higher pitched-sound to come out.
The data support the hypothesized convergence between heart rate and acoustic features of vole vocalization, and that vole vocalizations are able to convey information related to physiological state. This confirms that voles are able to monitor their acoustic features of their vocalizations (pitch and duration) as a result of autonomic activity. Therefore, when a vole is in a calm physiological state, it can shift its vocalizations towards longer durations and lower frequencies, signaling to conspecifics that they are safe to approach. A previous study found similar results in human infants, demonstrating a common mammalian adaptive behavioral system involved in regulating acoustic features of vocalizations and pathways regulating the heart.
Although the mechanisms mediating the covariation of vocalization is still unknown, the authors postulate that the vagus nerve and sympathetic nervous system are likely involved. In addition to vagal regulation as a variable that might moderate the relation between acoustic features of vocalizations, the authors would like to design an experiment that incorporates positive social cuing to see if there is a correlation between social behavior, heart rate, and modulation of acoustic frequencies. So, to answer the question raised in the title, you should avoid a vole with a fast heart rate because it could be in a bad mood and may start making threatening noises in high frequencies.
Stewart, A. M., Lewis, G. F., Yee, J. R., Kenkel, W. M., Davila, M. I., Carter, C. S., Porges, S. W. (2015). Acoustic features of prairie vole (Microtus ochrogaster) ultrasonic vocalizations covary with heart rate. Physiology & Behavior 138, 94-100.