Elephant seals have rhythm and they know how to use it
Seals identify breeding rivals by the rhythm of their vocal calls
New research published in the journal Current Biology finds that elephant seals identify one another by the rhythm in their calls, much the way humans can discern accents and vocal tone.
Previously there was no recorded example of a non-human mammal that could remember and recognize a wide range of rhythms.
"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," lead author Nicolas Mathevon of the Université de Lyon/Saint-Etienne in France said in a written statement.
"There have been experiments with other mammals showing that they can detect rhythm, but only with conditioning."
For this study, the researchers — including a team from the University of California Santa Cruz (UCSC) — spent years studying an elephant seal colony in Ano Nuevo State Park, about 90 kilometres south of San Francisco.
"This has been part of a really long term research project that began in the early 2000s," says co-author Caroline Casey, a PhD candidate in ecology and evolutionary biology at UCSC, who joined the project in 2009.
All about the breeding
"We started to ask questions about the important role that these calls play in the social lives of the animals … What information is actually encoded in these signals?"
Back in 2015 the team reported that individual males possessed "unique vocal signatures" — essentially calling out their own names during breeding season in a series of pulses, and asserting their places in the social hierarchy, she says.
Those places in that hierarchy are determined by violent fights between the males, which can be costly. Sometimes one opponent will be killed, but at minimum, the fights waste energy that would otherwise be devoted to breeding, says Casey.
That's because during that breeding season — when perhaps you've seen elephant seals sunning themselves while you're on your California vacation — they're actually in a two-month period spent out of the water without food or drink.
The researchers had previously established that the males listen to calls to determine if they should bother to assert themselves.
"If a male hears a call from another individual and he's lost to that individual previously, he knows to retreat without having to engage in battle," says Casey.
For this study, the group set out to learn more about what information is encoded in the vocal signals and how exactly the seals differentiate each other this way.
They found that the males use the duration between pulses in each other's vocal signals. The seals can discern fine rhythmic and tonal variations to determine whether to fight one another for a place on the rock with good access to the harem.
The researchers made the findings by recording the males' calls, modifying them to be slower or faster, and then playing them back for the seal colony. These are known as playback experiments.
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The changes to the calls resulted in different behaviour among the males. Some would flee the scene after hearing only minute changes to a vocal call, while others would stay put when faced with dramatic changes.
The diverse responses led the study authors to determine that the males are very sensitive to both rhythmic and tonal characteristics in identifying their rivals.
The research is unique because the scientists have observed the animals over such a long period of time, and the findings open the door to the possibility that other animals may also possess similarly sophisticated understanding of rhythm in their communication, says Casey.
'There's a reason we love these animals that we think are so fascinating. It's because we've discovered these amazing things that we didn't know were possible' - Caroline Casey, biologist at the University of California Santa Cruz
"We wouldn't have been able to do this had we not had years and years of data and knowledge of individual animals, and I really want to emphasize how important that is, especially as the scientific climate in the United States is changing," she says.
"It's just harder and harder to find people who are willing to support science … There's a reason we love these animals that we think are so fascinating. It's because we've discovered these amazing things that we didn't know were possible."