内容摘要：Bowhead whales are mysterious, Arctic-dwelling creatures. Scientists believe they can live for over

Bowhead whales are mysterious, Arctic-dwelling creatures. Scientists believe they can live for over two centuries, and even so, they largely avoid getting cancer. In the 1990s, an old stone spearhead -- a weapon that hadn't been used since the 1800's -- was found embedded in a bowhead whale's blubber. That whale had apparently survived a hunter's attack, over a century earlier.

Now, marine researchers say they've recorded bowheads singing an unprecedented number of songs. The marine mammals seem to be altering their songs each year, similar to how a jazz musician is constantly improvising.

“If humpback whale song is like classical music, bowheads are jazz," Kate Stafford, an oceanographer at the University of Washington, said in a press release.

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After listening to and analyzing three years of bowhead audio recordings, captured in Arctic waters east of Greenland, Stafford and her research team published their results on April 4 in the journal Biology Letters.

Whales are heavily reliant upon sound to communicate in their murky, undersea worlds. Humpback whale songs have been recorded extensively, and their haunting sounds can be heard online.

But as far as scientists can tell, humpbacks don't create such a novel diversity of songs each season.

"The sound is more freeform," said Stafford. "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."

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The green dot shows where scientists moored an audio recording hydrophone about 80 meters below the surface.Credit: Kate Stafford/University of Washington

Between 2010 and 2014, the bowheads were found singing 24 hours a day during the winter months. They sang mostly between November and March. The songs typically lasted between hours and days, and only rarely did a song continue to be in use for a month.

These song lengths might strike us as odd, since we're used to three and a half minute pop songs. But bowheads have developed their underwater cultures over millions of years, and like much of whale behavior, the meaning and structure of their songs remains cryptic.

"Why are they changing their songs so much?” asked Stafford. “In terms of behavioral ecology, it’s this great mystery."

Similar to some birds, the authors suggest that delivering song diversity might serve an adaptive advantage in attracting mates, though there's no evidence of this.

Bowhead whales are massive, plankton-eating mammals.Credit: UIG via Getty Images

The researchers also suggested that the bowhead's impressive song diversity could be due to an expanding population, with new whales developing new songs. Or, due to vanishing sea ice cover in the warming Arctic, bowhead populations aren't as separated by thick masses of drifting ice floes as they once were.

But these explanations, the authors say, still wouldn't explain how much the songs change within each season.

Bowheads, and their curious lives, remain mostly inaccessible to humans. For instance, they sing under sea ice during the Arctic winter when its dark all day. We simply can't see what they're doing, even when then the massive mammals surface for air.

"We would never have known about this without new acoustic monitoring technology," said Stafford.

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