Elephant seals 'recognise vocal rhythm'
Male elephant seals recognise the rhythm of one another's voices, researchers say.
Scientists in the US "decoded" the calls of male elephant seals, revealing that vocal communication played a crucial part in their social lives.
This showed seals communicating their identity with deep, rhythmic calls.
In their Current Biology paper, the team says this is the first example of non-human mammals "using rhythm" in everyday life.
Just as humans can identify a particular song based on its distinctive rhythm, this research revealed that male elephant seals could identify each other from the pulsing pattern of their calls.
Lead author Prof Nicolas Mathevon, from the University of Lyon and St Etienne, described these grumping vocalisations as "distinctive".
They were "very rhythmic, like a metronome", he told BBC News.
"In the colony, everyone knows who is who… they recognise the voice of all the other males in the colony."
And this is important in a congested beach colony - at the site the team studied, more than 4,000 seals are packed on to the beach, so it is important to know your neighbours.
Seal social networking
"If you think about the social life of a male elephant seal, it's actually quite complicated," said co-author Caroline Casey, from the University of California Santa Cruz.
"Within his own social network, he's potentially interacting with 20-30 other individuals."
In these situations, it can be crucial to distinguish quickly between dominant and subordinate males - to avoid a potentially lethal conflict.
"If he gets it wrong, the costs of that mistake are pretty high. We saw a male die last year from a canine through the skull," Ms Casey said.
In this context, the rhythmic call of a male elephant seal acts as a distinctive "fingerprint", helping other males decide whether to flee the vicinity.
The research team spent six years studying the colony of more 4,000 elephant seals in Ano Nuevo National Park, California.
They recorded the vocalisations of dominant males, then played back those calls through loudspeakers to subordinate males.
As expected, less dominant males fled the sound of the high status seals, which are referred to as "beachmasters".
Crucially though, when the researchers artificially modified the rhythm of a call, subordinate males no longer recognised it and did not respond.
If they did not recognise a voice, "they wait and see", said Prof Mathevon. "It's their strategy."
While doing nothing might seem lazy, this "very efficient strategy" is also potentially life-saving.
During the breeding season, elephant seals haul out from the ocean and stay in the colony for almost 100 days without any food or water.
So, if males do not recognise the rhythm of a call, they simply do not move, and therefore avoid a waste of vital energy.
Prof Patricia Gray, from the University of North Carolina, Greensboro, who was not involved in the research, said it had captured "natural animal behaviour in the wild" and shown how important producing and recognising rhythm was to their survival.
She added that understanding how other species used rhythm could "unlock many answers" about how they perceived other animals and their surroundings and how these qualities related to human perception.