Wikie, a 16-year-old female orca has been recorded copying words including "hello" and "bye"
The killer whale that can mimic human words is proof the "highly intelligent" mammals should be released from captivity, animal charities have said.
Wikie, a 16-year-old female orca that lives in a French marine theme park, has been recorded copying words such as "hello" and "bye," in what is believed to be a world first.
The research has prompted criticism from campaigners who argue the whales should not be imprisoned.
Claire Bass, UK director of the Humane Society International, said Wikie's ability to imitate human speech "is as tragic as she is fascinating."
"She is certainly further proof that these are highly intelligent mammals whose captivity in marine parks in the 21st century should come to an end," she said.
"She is also a painful reminder that in the wild where these awesome animals swim free, they communicate with each other using complex language and even group-specific dialects, natural communication that is utterly denied them in captivity."
People for the Ethical Treatment of Animals (Peta) said orcas belong in the wild where each family has its own "culture and a unique group dialect."
"How deeply ironic that this research, which speaks volumes of the emotional intelligence of orcas, was conducted in a marine park's cement cell, where they're imprisoned and denied everything that's natural and important to them in order to make money from tourists,” said the charity's director Elisa Allen.
"If we had the intelligence to understand her own sophisticated language, we would hear her calling to be free."
The experiments were carried out at Marineland Aquarium in southern France, which faced criticism in 2015 after one its killer whales died during flooding.
Last year the company vowed to fight a ban on breeding killer whales and dolphins in captivity, claiming it would harm its animals.
SeaWorld stopped breeding killer whales after facing heavy criticism of their treatment in the wake of documentary Blackfish.
Wikie is believed to be the first member of her species to mimic human speech.
The orca was taught to copy novel sounds and words from both another killer whale - her own three-year-old calf, Moana - and by humans.
She "spoke" while partially immersed in water with her blowhole exposed to the air.
The human words and phrases she attempted to copy included "ah ah," "hello," "bye bye," "Amy," "one two" and "one two three."
The scientist who led the study said it was conceivable that basic "conversations" with her may one day be possible.
Dr Jose Abramson, from Complutense de Madrid University in Spain, said: "We will gain more if we try to understand the natural way each species communicates in its own environment than if we try to teach a human language."