Harbour seals can learn how to change their voices to seem bigger

Consider the squeak of a mouse and the low rumble of a lion’s roar. In the animal kingdom, bigger animals usually produce lower pitch sounds as a result of their larger larynges and longer vocal tracts. But harbour seals seem to break that rule: they can learn how to change their calls.

That means they can deliberately move between lower or higher pitch sounds and make themselves sound bigger than they really are.

“The information that is in their calls is not necessarily honest,” says Koen de Reus at the Max Planck Institute for Psycholinguistics in Nijmegen, Netherlands.

An earlier study had shown that some pinnipeds, a group of animals that includes seals, sea lions and walruses, can learn new sounds or modify sounds that they hear. Now, de Reus and colleagues have shown that the vocal gymnastics of harbour seals are probably a product of vocal learning, not anatomy.

To investigate, the researchers examined the vocal tracts of 68 harbour seal pups (Phoca vitulina) that had died before reaching a year old. The seals came from Sealcentre Pieterburen, a seal rehabilitation facility in the Netherlands. In addition to looking at the animals’ vocal cords, the team also reviewed a collection of recorded seal sounds from animals they had weight information for to untangle any potential correlation between pitch and body size.

Their analysis revealed that there was no anatomical explanation for the seals’ tremendous vocal range. “We saw that there was no such structure that could help explain how they actually make and modify sounds,” says de Reus. Seals with as much as a 5 kilogram difference in body weight produced similar sounding calls. That left one explanation for the vocal gymnastics: they learned how to do it.

The ability to learn, modify and imitate new sounds is relatively rare, found only in animals such as humans, elephants, bats, seals, whales and some birds. The more we discover about other animals’ vocal abilities, the better we can understand the evolution of human speech, says de Reus. “I think that is one of the things that makes me excited to work on this project.” It is also another reason why it is so important to protect wildlife, he says.

Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.243766

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