In 1971, a Maine fisherman rescued a baby seal and spoke to him every day. 7 years later, that seal began talking back in his own voice

In 1971, a fisherman in Maine found a tiny orphaned harbor seal that needed help to survive. He took the pup home, fed him by hand and spent his early days talking to him. At the time, there was no way to know that those ordinary conversations would eventually become part of one of the most unusual animal communication cases ever recorded.

The seal was named Hoover after the fisherman, George Swallow, took him in near Bethel Point, Maine. Years later, Hoover became famous at the New England Aquarium in Boston for producing sounds that were remarkably close to human speech. What made the story even stranger was that researchers found that his voice appeared to resemble Swallow’s own rough Maine accent.

Hoover did not simply make sounds that people thought sounded like words. Scientific analysis later found that his vocalisations contained features associated with human speech, including the kinds of changes used to form vowels and consonants.

A fisherman raised the orphaned seal at home

Hoover was only a few weeks old when Swallow found him in 1971. The young harbor seal had lost his mother and needed to be cared for, so Swallow brought him home.

During those first weeks, Swallow bottle-fed the pup and regularly spoke to him. Hoover was therefore exposed to human speech at a very early stage of his life, long before anyone knew that this experience might matter.

But Hoover could not stay in the house forever. He grew quickly and eventually became too large to be safely kept there. In 1976, at about three months old, he was donated to the New England Aquarium in Boston.

For the next few years, Hoover lived at the aquarium without attracting the kind of attention that would later follow him.

Then Hoover started making human-like sounds

Around the time Hoover reached sexual maturity, staff began noticing something unusual.

The seal was producing sounds that resembled English phrases. His known repertoire included “hello there”, “come over here”, “hurry”, “hey hey” and even “Hoover”.

The discovery was unusual enough to attract scientific attention because this was not simply a case of people hearing familiar words in random animal noises.

Researchers examined recordings of Hoover using spectrograms, which allow scientists to visually analyse the characteristics of sounds. The results showed vocalisations with formant changes similar to those involved in human vowel and consonant production.

That made Hoover one of the strongest documented examples of a marine mammal learning to reproduce aspects of human speech.

And there was another remarkable detail. Hoover appeared to have picked up the voice of the person who had raised him. Reports described his speech as having an “unmistakable Maine accent”, with a gravelly quality resembling Swallow's voice.

Why did he wait years before speaking?

The biggest mystery was not only how Hoover could imitate human sounds, but why he did it years after being exposed to them.

Hoover had been hearing Swallow speak since he was a very young pup. Yet his speech-like vocalisations did not become apparent until much later, around the time he reached sexual maturity.

Researchers also noticed when Hoover was most likely to make these sounds. He generally produced them in the water, often from a vertical position and followed by bubble blowing. The behaviour was particularly common during the breeding season and was often directed towards female seals.

This led scientists to believe that Hoover was not necessarily using the phrases as humans use language in everyday conversation. Instead, the sounds may have functioned as a kind of breeding display, similar to the calls male seals use to attract females.

In other words, Hoover may have learned the sounds early in life but only started using them when he was old enough for them to serve a purpose.

His story has similarities with birdsong

The delay between learning sounds and producing them later is one reason Hoover became especially interesting to researchers studying vocal learning.

Dr Tecumseh Fitch, a specialist in language evolution, explained the unusual timing to IFL Science: “This time delay is reminiscent of bird song learning: young birds learn the song in the nest but don’t begin singing themselves until they mature.”

The comparison is important because vocal production learning is uncommon among mammals. It refers to the ability to change or develop vocal sounds by learning from other individuals.

Humans obviously do this when learning speech, while several bird species are well known for learning songs. Among mammals, however, the ability has been found in a much smaller group, including humans, pinnipeds such as seals and walruses, cetaceans, bats and elephants.

Hoover's case suggested that harbor seals may have more flexibility in controlling their voices than scientists had once assumed.

Hoover was not trained to talk

Another interesting part of the story is that aquarium staff did not train Hoover to copy human speech.

His sounds appear to have developed naturally after his early exposure to Swallow. Researchers have suggested that Hoover may have formed a strong vocal association with the fisherman during his early development.

Scientists still cannot say that Hoover understood the words he produced in the way a human speaker would. Vocal mimicry and understanding language are two different things.

What Hoover demonstrated was the ability to reproduce aspects of a sound he had heard, which is impressive in itself.

Research involving other pinnipeds has also found evidence of vocal flexibility. Harbor seal pups can change the pitch of their calls, while seals and walruses can be trained to produce sounds and imitate aspects of melodies and vowels. Grey seals have also shown an ability to modify their vocal tracts in ways that help reproduce human-like vowel sounds.

These findings suggest that Hoover may have been unusual, but perhaps not completely unique.