Harbour seals may sound different than expected from their body size. Is this ability related to their vocal talents or is it the result of an anatomical adaptation? An international team of researchers led by scientists from the Max Planck Institute for Psycholinguistics Nijmegen investigated the vocal tracts of harbour seals, which matched their body size. This means that harbour seals are capable of learning new sounds thanks to their brains rather than their anatomy.
Most animals produce calls that reflect their body size. A larger animal will sound lower-pitched because its vocal tract, the air-filled tube that produces and filters sounds, is longer. But harbour seals do not always sound like they look. They may sound larger — perhaps to impress a rival — or smaller — perhaps to get attention from their mothers. Are these animals very good at learning sounds (vocal learners), or have their vocal tracts adapted to allow this vocal flexibility?
To answer this question, PhD student Koen de Reus and senior investigator Andrea Ravignani from the MPI collaborated with researchers from Sealcentre Pieterburen. The team measured young harbour seals’ vocal tracts and body size. The measurements were taken from 68 young seals (up to twelve months old) who had died. The team also re-analysed previously gathered harbour seal vocalisations to confirm their impressive vocal flexibility.
De Reus and Ravignani found that the length of harbour seals’ vocal tracts matched their body size. There were no anatomical explanations for their vocal skills. Rather, the researchers argue that only vocal learning can explain why harbour seals do not 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 findings from acoustic and anatomical data may help us to identify more vocal learners,” says de Reus. “Studying different vocal learners may help us to find the biological bases 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 capacities,” adds Ravignani.