Most animals produce calls that reflect their body size. A larger animal will sound lower because its vocal tract, the air-filled tube that produces and filters sound, is longer. But harbor seals don’t always sound like they look. They may appear larger – perhaps to impress a rival – or smaller – perhaps to get their mother’s attention. Are these animals very good at learning sounds (vocal learners), or do they have their vocal pathways adapted to allow for this vocal flexibility?

To answer this question, doctoral student Koen from Reus and lead researcher Andrea Ravignani from MPI collaborated with researchers from the Sealcentre Pieterburen. The team measured the vocal tracts and body size of young harbor seals. Measurements were taken from 68 young seals (up to 12 months old) that had died. The team also re-analyzed previously collected harbor seal vocalizations to confirm their impressive vocal flexibility.

De Reus and Ravignani found that the length of the vocal tracts of harbor seals corresponded to their body size. There was no anatomical explanation for their vocal skills. Instead, the researchers say that only vocal learning can explain why harbor seals don’t always sound like they look.

“Vocal learners will sound different from their body size, but the size of their vocal tracts will match their body size. The combined results of acoustic and anatomical data can help us identify more vocal learners,” says de Reus. “Studying different vocal learners can help us find the biological basis of vocal learning and shed light on the evolution of complex communication systems, such as speech.” “The more we look, the more we see that seals have something to say about human speech abilities,” adds Ravignani.

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