Elephant rumble choruses
African elephants are highly social animals, and much of their communication happens via low-frequency rumbles that can carry over long distances. Around 60% of rumbles are produced in choruses where several elephants call at once. Because overlapping calls are so hard to pull apart, choruses have received relatively little scientific attention.
Together with Joyce Poole and Mickey Pardo from ElephantVoices and the research team at ESP, I investigated how we can use machine learning to determine what elephants are doing based on their vocalizations alone. We used recordings of elephant calls collected in Amboseli, Kenya, each paired with detailed observations of who was calling and what the herd was doing at the time. By training models on these ground truth examples, our algorithms could successfully predict the social context, including things like greeting one another after a group had been separated for a long period, contact calling over long distances to stay in touch while out of sight, comforting or reassuring calves, or developing a shared plan of action such as where to go next.
In addition to being able to predict elephant behavior from chorus audio, we also found that in some situations elephants’ calls become more acoustically similar to one another as a rumble exchange unfolds. Interestingly, this happened primarily in contexts in which elephants are coordinating with one another, which suggests that this pattern of vocal convergence might be a way that elephants can "get in tune" with one another in order to handle herd logistics and coordinate group decisions.
This kind of vocal convergence, where different individuals adjust their speech or vocalizations to more closely resemble those of whoever they're talking to, also occurs in humans. In people, vocal convergence can occur on multiple levels (e.g., syntax, word choice, speech rate, and other acoustic-phonetic characteristics), and is thought to signal social closeness between speakers. It's fun to see similarities between us and other species, and also a nice reminder that communication is dynamic, layered, and doesn't occur in a vacuum. I imagine that future studies will find this kind of convergence in interspecies exchanges as well, especially when animals are cooperating or coordinating with each other.
