Have you ever heard of a dog barking softly? Unless a dog’s vocal cords are damaged or in ill health, it can really only bark loudly. Humans, however, are able to modulate the tone of their voices and speak loudly or softly at will. Surprisingly, a new study indicates that baby seals may be able to do the same.
In this study, eight harbor seal pups between one and three weeks of age were exposed to noises of different intensities. The pups were held in a rehabilitation center (the Dutch Sealcentre Pieterburen) prior to being released back into the wild.
To investigate whether the baby seals could adapt their voices to noises in the environment, the researchers recorded noises from the nearby Wadden Sea and then played these noises back to the pups for several days.
The recordings were played back at three different levels of loudness (from no sound to 65 decibels). The pitch of the sea sounds was kept at the same level as the regular pitch of the seals pups’ calls. The researchers also recorded the spontaneous calls by the baby seals.
Analysis of the recordings showed that when the seal pups heard louder sea noises, they lowered their tone of voice. The pups also kept a steadier pitch with the more intense noise levels.
One seal behaved in the opposite manner and produced louder calls when the noise got louder. This is known as Lombard effect and it is typical in human speech when people raise their voices against a background noise, in order to be understood better. The pups did not produce more or longer calls when they heard different levels of sea noise.
Overall, however, it was clear that young seals adapted to the noises in their environment by lowering the tone of their voice – an ability they seem to share with humans and bats. Other animals in similar experiments only raise their voice (in other words, make louder calls) in response to louder noise.
“Seal pups have a more advanced control over their vocalizations than assumed up until now,” noted study senior investigator Andrea Ravignani, scientist at the Max Planck Institute for Psycholinguistics.
“This control seems to be already present at only few weeks of age. This is astonishing, as few other mammals seem capable of that. To date, humans seem to be the only mammals with direct neural connections between the cortex (the outer layer of the brain) and the larynx (what we use to produce tone of voice).”
“These results show that seals may be the most promising species to find these direct connections, and unravel the mystery of speech.”
“By looking at one of the few other mammals that may be capable of learning sounds, we can better understand how we, humans, acquire speech, and ultimately why we are such chatty animals.”
The results of the study were published today in the Philosophical Transactions of the Royal Society B; Biological Sciences.