After recording wind sounds and other ambient noises on a sandbank in the Wadden Sea
— located among Denmark
, Germany and the Netherlands
— the researchers used computer software to filter the recorded audio to a frequency that would overlap with the formant range of seal pups
’ mother attraction calls
” is a characteristic component of the quality of a speech sound
The authors then tested eight wild-born, healthy and unrelated harbor seals that were between 1 そして 3 weeks old and from the Seal Rehabilitation and Research Centre in the Netherlands. This center ultimately releases seals back into the wild.
As the seals heard a speaker play a 45-minute recording consisting of high noise, low noise or no playback over several days, they spontaneously called out. When the pups heard louder sea noises, they lowered their vocal pitch. During more intense noise levels, the pups used a steadier pitch — and one seal raised its voice. This behavior, called the Lombard effect, is typical for human speech when people talk louder to be more understandable, the authors said.
The seals might have lowered their pitch since lower-frequency sounds travel farther in windy environments like the one projected by the recorded audio, said Caroline Casey, a research scientist and adjunct professor at the University of California, Santa Cruz’s Institute of Marine Sciences and ocean sciences department. Casey independently peer-reviewed the study but wasn’t involved in the research.
“または (the lower pitch
) could help retain the pups
’ identities since the fundamental frequency is a characteristic that’s strongly related to the identity and size of that pup
,” 彼女は付け加えた. In this context
, fundamental frequency describes an animal’s vocal frequency range dependent on the speed
, size and use of its vocal cords
The findings showed that “seal pups have a more advanced control over their vocalisations than assumed up until now,” Ravignani said in a statement. “This control seems to be already present at only (A) few weeks of age. This is astonishing, as few other mammals seem capable of that.”
以前は, humans were thought to be the only mammals with direct neural connections between the cortex — the outer layer of the brain — and the larynx, which we use to produce vocal tone, 彼が追加した. “These results show that seals may be the most promising species to find these direct connections, and unravel the mystery of speech.”
In studying which neural networks or social conditions need to be in place for language to evolve, birds have been the best animals to compare ourselves to, Casey said. That’s because during studies on environment and vocal learning or plasticity, birds — unlike most mammals — can be raised in captivity and naturally mature faster due to their short lifespans.
“しかしながら, there’s a lot of differences, especially with respect to sociology and life history between humans and birds,” 彼女は付け加えた. “We’re always looking for mammals that would be good models for the study of vocal learning.”
There haven’t been many studies on how plastic young animals’ calls can be. と “most studies, especially in the wild, you don’t actually know the age or sex sometimes of the animals that you’re recording, so it’s very difficult to get high-quality recordings of animals from different age classes,” Casey added. “Being able to look at that in this really young age group is very unique.”
Future research, 著者は書いた, could further explore what other factors might be important for harbor seals’ vocal plasticity.