Wikie, a 16-year-old captive orca living in a French marine theme park, can be heard in recordings mimicking words such as “hello” and “Amy”, and counting “one, two, three”.
The sounds emerge as parrot-like squawks, shrill whistles or raspberries, but most are clear enough to understand.
Although the researchers did not set out to test Wikie’s communication skills, the scientist who led the study believes basic “conversations” with her may one day be possible.
Dr Jose Abramson, from Complutense de Madrid University in Spain, said: “Yes, it’s conceivable ... if you have labels, descriptions of what things are. It has been done before with a famous grey parrot and dolphins using American sign language; sentences like ‘bring me this object’ or ‘put this object above or below the other’.
“But you have to be careful about imposing our human concepts on animals. 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.”
Wild killer whales are known to live in groups with unique vocal “dialects” — learned sounds used for communication that are kept within a particular population and passed to future generations.
Experts see these differences as cultural and believe they demonstrate a high level of social intelligence.
Killer whales both in the wild and in captivity have also been observed copying dolphin calls and the barks of sea lions.
However, Wikie is believed to be the first member of her species to mimic human speech.
The experiments, carried out at her home at Marineland Aquarium in Antibes two years ago, are reported in the journal proceedings of the Royal Society B.
Wikie, who had taken part in previous behavioural studies, 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.
Making sounds outside her natural medium she found some of the unfamiliar whale noises more difficult than human words, said Dr Abramson.
In each trial, Wikie was given a “do that” hand signal by a researcher, but offered no food rewards. The human words and phrases she attempted to copy included “ah ah”, “hello”, “bye bye”, “Amy”, “one two” and “one two three”.
Speech recognition software was used to test how well she performed.
Dr Abramoson said: “Intelligence is a controversial subject and difficult to define. You can say that AIs are more intelligent than humans because they win at chess, but that’s just one type of cognitive capacity.
“In human intelligence, cultural and social learning aspects are very important. We can say that killer whales and other cetaceans have a highly developed social intelligence.”
He stressed that once tool-use was seen as a uniquely human hallmark of intelligence, but now the focus had shifted to social mental ability.
“Machiavellian behaviour, making friends, belonging to groups, manipulating others and competing — you don’t need hands for that,” he said.
– PA