Group dynamics, behavior, and tidal state drive calling in Cook Inlet beluga whales

Communication allows social species to exchange information among group members. In aquatic environments, acoustic signals are among the most effective forms of communication and are important for many species, including cetaceans. Beluga whales ( Delphinapterus leucas ) are highly social and vocal, yet little is known about the functionality of their social calls. To examine context-dependent vocal behavior in belugas, we collected passive acoustic data and fine-scale behavioral observations for the endangered Cook Inlet beluga population. The resulting dataset includes 1,720 annotated vocalizations collected during 1,051 minutes over 21 behaviorally encoded encounters. We fit generalized linear mixed models to investigate the effect of behavioral state, group size, calf presence, and tidal state on 1) calling rate (number of calls/minute) and 2) call category (whistles, pulsed calls, combined calls). Belugas were more likely to call when traveling and had higher calling rates during flood tides. Group-level calling rate increased sublinearly with group size, suggesting that individuals called less in larger groups, possibly reflecting increased listening or vocal coordination. We qualitatively illustrate that group calling rate increased before behavioral transitions, suggesting a possible link between vocal communication and group-level decisions. Whistles were more prevalent when traveling, while pulsed calls were more prevalent when milling. Further, combined calls occurred only when calves were present, indicating the importance of these calls in communication with calves. Identifying these communication patterns and the social, behavioral, and environmental contexts in which they occur can aid in our understanding and conservation of belugas and social marine species more broadly.