Bowhead whales communicate via a "freeform" and diverse singing style, scientists have discovered.
Researchers likened the sounds made by a population of the Arctic marine mammals to jazz music after they were recorded in song as they swam under ice off the eastern coast of Greenland.
Between 2010 and 2014 the scientists made recordings of 184 songs, each one different from the others.
Lead scientist Dr Kate Stafford, from the University of Washington, US, said: "If humpback whale song is like classical music, bowheads are jazz.
"The sound is more freeform. And when we looked through four winters of acoustic data, not only were there never any song types repeated between years, but each season had a new set of songs."
Experts draw an important distinction between animal songs and calls. Songs, usually associated with birds, involve complex musical phrases that must be learned.
True singing is not a common whale trait, despite widespread use of the term "whale song".
The only other whale known to have real singing ability is the humpback, which produces melodious songs common to each male population that change each spring.
The scientists expected the songs of the 200-strong bowhead whale population to follow a similar pattern. Instead, they found that the bowheads had a far more intricate, complex and ever-changing repertoire.
A previous study by the same team provided the first real evidence of the whales' talent in 2012.
Speaking of the earlier research, Dr Stafford said: "We were hoping when we put the hydrophone out that we might hear a few sounds.
"When we heard, it was astonishing: bowhead whales were singing loudly, 24 hours a day, from November until April. And they were singing many, many different songs."
The "Spitzbergen" bowhead population was hunted almost to extinction in the 1600s, but the audio recordings indicate that it has now returned to a healthy size.
For the study, hydrophones were moored at a depth of 80 metres (262ft) in the Fram Straight between Greenland and Norway. They were used to record the whales as they sang under thick ice during the continually dark winter breeding season.
The new research is published in the Royal Society journal Biology Letters.
Like birds, the bowhead whales may be singing to attract mates or defend territory. But the scientists admit there is still a lot to discover about the jazzer whales.
Whether only males sing, whether any songs are shared between individuals, and why the tunes continually change are all unanswered questions.
