The researchers were studying a 14-year-old female killer whale named Wikie, who was well-trained and had been taught how to copy behaviours in a previous study.
Wikie was recorded mimicking English words like “hello”, “bye bye” and “one two”, as well as the name of her trainer, Amy.
“Killer whales use their blowhole to make noises, almost like speaking out of your nose, so we were not expecting it to be perfect,” said Dr Jose Abramson, a researcher at the Complutense University of Madrid, who led the study.
Imitating vocal sounds in this way is a key component of language, and the ability to do so is rare in mammals besides humans.
Despite their intelligence, other primates are not generally capable of such imitation.
However, cetaceans – the mammal group that includes whales and dolphins – are known to be highly adept when it comes to vocal imitation. Both bottlenose dolphins and beluga whales have been observed copying noises they are exposed to.
“We still don't fully understand why some animals learn to mimic, but there are a few possibilities," said Dr Alex Thornton, a senior lecturer in cognitive evolution at the University of Exeter who was not involved in the study.
Some animal imitate others to deceive them, while other animals appear to do so in order to show off to potential mates, according to Dr Thornton.
“In some cases copying sounds might help to identify an individual as a member of a group," he said, explaining the dialects of whales help to mark them out as members of specific groups.