Humans aren't alone in using rhythm to communicate social information to one another. It turns out that male elephant seals are very tuned into the rhythm of each other's aggressive grunting – for good reason, as it can save their lives.
The seals engage in bloody battles to win the chance to mate with a female. The larger and more vicious males are recognised by their calls, which is enough to make smaller males flee.
Now scientists have found that the unique rhythm and pitch of the males' call can be recognised by other males, who decide whether or not to stay and fight based on who appears to be grunting at them. The results are published in the journal Current Biology.
Scientists played back recordings of male elephant seal calls – technically known as 'roars', despite sounding a lot more like grunts – to other males in the vicinity. They found that if they slightly altered the pitch and tempo of the calls, the smaller males would scarper quickly. If they altered the calls more dramatically – so they were obviously not the large male's ordinary call – the other males would stay put.
This decision can make or break it for a male. Stick around when it's a large alpha male and you put yourself at risk of death when he attacks. Run away too quickly when it's not a more dangerous male, and you lose out on a precious mating opportunity.
Elephant seals are the only mammals besides humans discovered to use rhythm in this way to identify each other.
"This is the first natural example where on a daily basis, an animal uses the memory and the perception of rhythm to recognize other members of the population," said study author Nicolas Mathevon of the University of Lyon, Saint-Etienne, in a statement.
Other experiments have shown that animals can identify rhythm, but only if they are taught to do so through many repetitions. But it could be that there are many other animals that understand and use rhythm in communication that we just haven't found out about yet.
"It is possible that maybe the ability to perceive rhythm is actually very general in animals, but it's extremely important for elephant seals, to the point of survival," Mathevon said.
"Competing for females, the males fight very violently, even to the point of killing one another. So it's very important for them to accurately recognise the voices, to be able to choose the right strategy, to know to avoid a fight with a dominant male, or even to start a fight with an inferior one."