Seals are one of the very few mammals to change the tone of their voices, allowing them to mimic humans like a parrot, scientists have found.

The sea creatures change the pitch of their calls depending on the sounds of their surroundings, according to a new study.

Seals can be taught to copy human speech like parrots, barking catchphrases in gruff accents like "come over here."

But while vocal learning, the ability to mimic sounds, is a rare trait among mammals, only a few species can adjust their voice's pitch to sound higher or lower.

Now scientists at the Max Planck Institute for Psycholinguistics have found seal pups are on the short list of animals with volume control.

Senior author Dr Andrea Ravignani said, "By looking at one of the few other mammals who may be capable of learning sounds, we can better understand how we, humans, acquire speech, and ultimately why we are such chatty animals."

Eight harbor seal pups aged one to three weeks old who were being held in a Dutch rehabilitation center before being released back into the wild were studied by the researchers.

They recorded noises from the nearby Wadden Sea before playing them back to the pups at volumes ranging from no sound to 65 decibels, but keeping the same tone height as the animal's calls.

They then recorded the pup's spontaneous calls to see whether they changed their tone of voice to match the sea sounds.

Seal pups lowered their tone of voice and kept a more steady pitch when hearing louder sea noises, the researchers found.

But one of the animal's displayed the so-called Lombard effect, producing louder calls when the noise got louder.

This is also typical of human speech, as people generally raise their voices to be better understood in noisy situations.

Dr Ravignani said, "Seal pups have a more advanced control over their vocalizations than assumed up until now.

"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."

Pups did not however produce more or longer calls when exposed to different levels of sea sounds.

Dr Ravignani said of the findings, published in the Philosophical Transactions of the Royal Society B: Biological Sciences, "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."

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