Triggers and consequences of wolf (Canis lupus) howling in Yellowstone National Park and connection to communication theory

Animal vocal communication is rife with concepts that, while important, are difficult to evaluate in nature. Particularly interesting is their application to large social mammalian carnivores characterized by year-long, loud vocalization. Here, we quantified triggers and consequences of 504 wolf (Canis lupus Linnaeus, 1758) howl events in Yellowstone National Park observed across 16 years. We related our results to two general theories of animal communication: that vocalization is more about communicating emotional/motivational states than a purposeful transfer of detailed information and that flexibility in use of long-distance vocalizations has been important to overall behavioural plasticity and advanced sociality in non-human primates and large social carnivores. In our study, half the howl events were triggered by 12 different environmental or social situations, most of which generated levels of anxiety. The remainder were non-triggered, apparently motivated internally but in contexts that reflected basic adaptive drives such as bonding and pack coordination. Approximately half of all howl events elicited either a change in sender activity or responding howls or travel from distant wolves, which we quantified. Wolf howling was inconsistent (low percentage of occurrence) in most behavioural contexts, hence demonstrating flexibility and social discrimination in its use. Thus, both theories were strongly supported.