Wild African savannah elephants appear to harmonize their deep, low-frequency rumbles when they join together in choruses, tuning their voices to sound more alike as the group vocalization unfolds, according to a new machine learning study. The research, published in Scientific Reports, also found that this vocal convergence is most likely to occur during specific social situations — such as when elephants reconnect after being separated or when they coordinate group movements — suggesting the calls may help families build a shared plan of action.
The findings offer fresh insight into how elephants communicate and navigate their complex societies, said Sara Keen of the Earth Species Project, a US non-profit that uses artificial intelligence to decode non-human animal communication. «It's sort of like what humans do in conversation, where you almost start to adopt the speaking patterns or accents of whoever you're interacting with,» Keen said.
Elephants communicate through a rich repertoire of body language and a wide range of sounds, including their iconic trumpet call and throatier roars. But the most common call is the rumble — so low-pitched it is often undetectable by humans — which can travel up to 10 kilometers, transmitting long-distance information that may include the caller's identity and what is happening at the time.
Scientists have long been intrigued by the way elephants rumble together in choruses, said Joyce Poole of Elephant Voices, a Washington DC-based non-profit that promotes the study and protection of elephants. Studying those complex sounds, however, proved extremely difficult because it is hard to pick out any given rumbling elephant in the chorus — what researchers call «the cocktail party problem.»
With significant developments in machine learning, Poole, Keen and their colleagues found that computers are up to the task. They used a collection of 902 recordings of rumbles gathered across four decades, emitted by wild female African savannah elephants from dozens of family groups in Kenya's Amboseli National Park. The calls were grouped according to six distinct social situations: staying in contact while separated; preparing to move; coordinating what to do next; comforting or reassuring calves; greeting close family members; and participating in large family reunions.
Machine analyses revealed that elephant choruses carry multiple layers of information at once and vary in a way that suggests they encode information about what a family is doing together and what happens next, Keen said. By tracking the rumbles of individual elephants within the same chorus, the data showed that in some cases the calls became more acoustically alike as the chorus progressed. This convergence occurred specifically when elephants were staying in contact while separated, coordinating what to do next, and greeting after a separation.
This suggests that vocal convergence may play a role in helping elephant families build a plan of action, Keen said. Earlier research published by Poole and her colleagues in 2005 showed that elephants can learn to imitate each other's voices when calling more generally; the new work shows that this imitation involves the rumbles, too.
Combined with other communication tools, including body language, the rumbling calls seem to help facilitate complex social interactions. «They appear able to negotiate, agree and disagree — and make a plan of action,» Poole said.
The findings not only shed light on elephant communication and cognition but could also eventually aid conservation by helping researchers track their behavior and movements remotely, the team says. Because rumbles allow for long-distance communication, elephants' ability to unite through their voices is an exciting reflection of their advanced cognition and evolution in their environment, said Andrew McLean, a member of the International Union for Conservation of Nature's Asian Elephant Specialist Group. «Evolving and elaborating this for social cohesion, group survival and foraging efficiency is very adaptive,» he said. «This is a fascinating finding — although it's not really surprising, given how intensely social elephants are.»