NOAA Fisheries announced Tuesday it is denying a request made by the Georgia Aquarium in Atlanta for 18 beluga whales (not pictured here) from Russia for public display. (Photo : Reuters)

A new study finds that a white male Beluga whale has learned to imitate the human voice.

Birds are known to mimic human voices, but for the first time it is shown that whales might also imitate human sounds.

"Our observations suggest that the whale had to modify its vocal mechanics in order to make the speech-like sounds," said Sam Ridgway of the National Marine Mammal Foundation.

"Such obvious effort suggests motivation for contact," he said.

NOC, the white Beluga whale, lived in captivity for 30 years at the National Marine Mammal Foundation in San Diego, California, until it died in 2007.

In 1984, Ridgway and his colleagues heard human-like voices in the close vicinity of the Beluga whale when there was no one else nearby. The sounds resembled people conversing at a distance but could not be heard clearly.

It was confirmed that the sounds belonged to NOC, when a diver came out of the whale enclosure believing that somebody told him to "get out." They were surprised when the sound was traced to NOC, as whales are known to emit sounds that are different from humans.

Ridgway and his team fed the whale with snacks in order to fit a device within his nasal cavity (similar to that of the human windpipe) to record his sounds. They have studied these audio recordings for the last three decades.

The unusual sounds revealed a rhythm similar to human speech. The fundamental frequencies displayed were several octaves lower than the normal whale sounds, but resembled more like the human voice, said the experts.

"Whale voice prints were similar to human voice and unlike the whale's usual sounds," Ridgway said.

"The sounds we heard were clearly an example of vocal learning by the white whale."

According to the researchers, NOC emitted the sounds by blowing up his air sacs to a higher level than while making normal sounds.

It is still unclear why the whales mimic the human voice. Marine biologist Peter Tyack, of the University of St. Andrews in Scotland, UK, suggested that the human-mimicking behavior could be a side effect of the marine animal's ability to imitate each other, reported National Geographic.

The findings of the study, "Spontaneous human speech mimicry by a cetacean," are published in the journal Current Biology.