Harbour seals can learn how to change their voices to seem

The vocal gymnastics of harbour seals, including the ability to significantly raise or lower their pitch, seem not to be down to anatomy but learning from one another

By Corryn Wetzel

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 (Phoca vitulina) seem to break that rule: they can learn how to change their calls, according to new research by a team at the Max Planck Institute for Psycholinguistics in Nijmegen, Netherlands.

That means they can deliberately move between lower or higher-pitch sounds, sometimes presenting larger than they really are.

“The information that is in their calls is not necessarily honest,” says Koen de Reus, a co-author of the new research.

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. This new work by de Reus and colleagues reveals that their vocal gymnastics are likely a product of vocal learning, not anatomy.

To figure this out, the researchers examined the vocal tracts of 68 seal pups under a year old. The already-deceased seals were provided by 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 seal sounds to untangle any potential correlation between pitch and body size.

Their analysis revealed that there was no anatomical explanation for their 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 kg 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, de Reus says: “I think that is one of the things that makes me excited to work on this project.” It’s also another reason why it’s so important to protect wildlife, he says.

Journal reference: Journal of Experimental Biology; DIO:10.1242/jeb.243766

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