Seals are very vocal and musical animals. Baby seals have been known to sing low notes to get attention, and their knack for being noisy sets them apart from other animals. Biologists believe that the ability to produce new vocalizations is a key ingredient to the evolution of human speech, and only some animals like song birds and humans can learn new vocalizations while maintaining a sense of rhythm.
“We know that our closest relatives, non-human primates, need to be trained to respond to rhythm,” Laura Verga, a postdoctoral researcher in the comparative bioacoustics department at Max Planck Institute for Psycholinguistics, said in a statement. “And even when trained, primates show very different rhythmic capacities to ours”.
But can adorable and musically-gifted baby seals pick up on rhythmic tones? Verga is the first author of a study published today in the journal Biology Letters outlines how harbor seals (Phoca vitulina) pick up on rhythmic patterns in various audio samples.
She and her team created three audio sequences with three different rhythmic properties: tempo, length, and regularity. Tempo is the speed of the music or how many beats a song has per minute, while length includes the duration of musical notes or whether a song is short or long. Regularity is whether or not a song or musical pattern is more steady like a metronome or loose like improvisational jazz.
The team wanted to see if infant seals would react to these various rhythmic patterns. They studied 20 seals from the Seal Rehabilitation and Research Centre (Sealcentre Pieterburen), a wildlife rescue and rehabilitation center in Pieterburen, Netherlands, before the pinnipeds were released back into the wild.
They recorded how many times the seals turned their heads to look at the source of a sound behind their backs, a method used in studies of human infants. The turning indicates that the seals find the stimulus interesting. If seals can discriminate between different rhythmic properties, they might look longer or more often when they hear a sequence they prefer.
The seals happened to look more frequently when the vocalizations were faster, longer, or rhythmically regular. According to the study, this means that baby seals were able to spontaneously discriminate between regular and irregular sequences, those that contained short notes versus long notes, and sequences with fast versus a slow-paced tempo. Unlike their primate counterparts, the seals did this without training or rewards, suggesting that it could be an an innate behavior.
“Another mammal, apart from us, shows rhythm processing and vocalization learning,” said Verga. “This is a significant advance in the debate over the evolutionary origins of human speech and musicality, which are still rather mysterious. Similarly to human babies, the rhythm perception we find in seals arises early in life, is robust and requires neither training nor reinforcement.”
The next steps for Verga and her team are to decipher whether seals perceive rhythm in abstract sounds or the vocalizations of other animals, and if other mammals show the same skills.
“Are seals special, or are other mammals also capable of spontaneously perceiving rhythm?” she asked.