Baby seals change their voices to be understood, study shows

A person or animal using this property is to be what is called “vocal plastic”, or adjust their voice signals in response to environmental changes that overlap or obscure their voices, according to the study published Monday in the journal Philosophical Transactions of The Royal Society B Being able to communicate clearly and accurately is important for mating opportunities, escape from predators and social learning, the authors wrote.
The researchers had a number of reasons for wanting to test the woodpecker seal’s voice notch. The rare ability to mimic new sounds – vocal learning – was previously seen among adult harbor seals and a few other mammalian species, according to the authors. And very few mammals have the capacity to change their vocal pitch to sound louder or lower, which is essential for human communication.
“By looking at one of the few other mammals that may be able to learn sounds, we can better understand how we humans acquire speech, and ultimately why we are such talkative animals,” said Andrea Ravignani, the study’s senior researcher and a research group leader in the comparative bioacoustics department at the Max Planck Institute for Psycholinguistics, in a statement.

Pinnipeds – animals such as seals and walruses that belong to the order Pinnipedia – are good models for vocal learning, as they are closer than other species to humans in terms of evolutionary development and diversification, the authors wrote.

After recording wind sounds and other ambient noise on a sandbank in the Wadden Sea – located among Denmark, Germany and the Netherlands – the researchers used computer software to filter the recorded sound to a frequency that would overlap with the seal pups’ formant area. ‘calls mother attraction. “Formant” is a characteristic component in the quality of a speech sound.

The authors then tested eight wild-born, healthy and unrelated spotted seals that were between 1 and 3 weeks old and from the Seal Rehabilitation and Research Center in the Netherlands. This center eventually releases seals back into the wild.

Adult harbor seals can weigh up to 285 pounds (over 129 kg) and grow up to 6 feet (1.8 meters) long.

When the seals heard a speaker play a 45-minute recording consisting of loud noise, low noise or no playback over several days, they shouted spontaneously. When the puppies heard louder sea sounds, they lowered their voices. During more intense noise levels, the young used a more stable pitch – and a seal raised its voice. This behavior, called the Lombard effect, is typical of human speech when people speak louder to be more understandable, the authors said.

The seals may have lowered their pitch as lower frequency sounds travel further in windy environments such as those projected by the recorded sound, said Caroline Casey, a researcher and adjunct professor at the University of California, Santa Cruz’s Department of Marine Science and Marine Science. Casey has independently peer-reviewed the study, but was not involved in the research.

“Or (the lower pitch) could help preserve the puppies’ identity, as the fundamental frequency is a trait that is strongly related to the identity and size of that puppy,” she added. In this context, fundamental frequency describes an animal’s voice frequency range depending on the speed, size, and use of its vocal cords.
Spotted seals have a lifespan of about 25 to 30 years.

The results showed that “seal puppies have more advanced control over their vocalization than previously thought,” Ravignani said in a statement. “This control appears to be already present at only (a) few weeks of age. This is astonishing as few other mammals appear to be capable of it.”

In the past, humans were considered to be the only mammals with direct neural connections between the cortex – the outer layer of the brain – and the larynx that we use to produce vocal tone, he added. “These results show that seals may be the most promising species to find these direct connections and unravel the mystery of speech.”

By studying what neural networks or social conditions need to be in place for the language to evolve, birds have been the best animals to compare us to, Casey said. This is because during studies of environment and vocal learning or plasticity, birds – unlike most mammals – can be bred in captivity and naturally mature more quickly due to their short lifespan.

“However, there are a lot of differences, especially in terms of sociology and life history between humans and birds,” she added. “We are always looking for mammals that would be great models for the study of vocal learning.”

There have not been many studies of how plastic young animal calls can be. With “most studies, especially in nature, you do not actually know the age or sex sometimes on the animals you record, so it is very difficult to get high-quality recordings of animals from different age groups,” Casey added. “Being able to look at it in this really young age group is very unique.”

Future research, the authors wrote, could further explore what other factors may be important to the vocal plasticity of harbor seals.


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