For this research, Ravignani designed a playback experiment. This is a technique also used to understand the cognition of pre-verbal human infants, in which sounds are played to the test subject while the sounds’ acoustic features are varied experimentally and the infant (or, in this case, seal) response is measured. Ravignani tested a four-week-old seal pup – Aguanile – which, unlike others at the Sealcentre Pieterburen in the Netherlands, was housed alone. Ravignani prepared audio tracks that contained voices of other pups along a gradient of geographical proximity. These calls were looped following different rhythmic structures to test how Aguanile would react if, for instance, the simulated animals were vocalising more quickly or slowly, or more or less predictably. This allowed Ravignani to show that Aguanile learnt the rhythm of the simulated pups and timed its calls accordingly to avoid talking over them.
Novelty in (animal) communication
With this work, Ravignani offers a new angle to the theory of animal (and human) communication. “While most research in the past tackled issues concerning the spectral dimension of communication (for example, how loud a sound is or what pitch it has), this research looked at a formerly neglected dimension: rhythm, or how sounds are organised in time, possibly in an interactive way with other individuals of the same species engaging in communication. This research shows that the rhythmic dimension in seal communication is at least as important as, if not more important than, the spectral dimension.” Furthermore, it helps us to better understand the behaviour of young seals. Until now, the pups’ noises were considered to be crying, but that’s not correct. The findings also have interesting implications for the study of the origins and evolution of the human capacity for language and music. Since this cannot be studied directly by travelling back in time, comparative animal work can show the function of similar behaviours in other species.
Since his paper was submitted for publication, Ravignani has tested more seal pups. Results suggest that other pups show interactive vocal behaviour similar to Aguanile. No animal was stressed or harmed for this experiment. The playback test simply simulates an auditory landscape which pups are continuously exposed to, namely the voices of other pups.
The Sealcentre Pieterburen in the Netherlands is one of the largest seal rehabilitation centres in the world, where sick or orphan seals are taken care of and treated. They typically spend two to three months there before being released back into the wild.
Andrea Ravignani, PhD
Artificial Intelligence Lab of Vrije Universiteit Brussel
All photo credits go to: Beatriz Rapado Tamarit & Margarita Méndez Aróstegui