In the ocean videos we've become accustomed to, the sounds of the sea are fairly simple: the whoosh of bubbles as a shark darts after a seal, the splash of a breaching dolphin, the British accent of a BBC narrator.
But for Kate Stafford and other oceanographers who have spent their careers eavesdropping on the sounds of marine animals, ocean noise is as complex and multifaceted as the sounds of a jungle.
And bowhead whales — 75-ton, thick-bodied mammals that can live two centuries and grow to be as long as a tractor-trailer — are the world's biggest songbirds.
Stafford revealed in a paper released this week that bowhead whales near Greenland are part of the small group of animals that make complex "singing" sounds.
"Under 100 percent sea ice, in the dead of winter, bowhead whales are singing," Stafford, a professor at the University of Washington, said in a 2016 Ted Talk.
Lots of animals make sounds, of course. They sing to mates, or snarl at predators or scream out warnings to others. It's rare for animals to make what Stafford's paper called "multiple frequencies and amplitude-modulated elements combined into phrases and organized in long bouts." That's science-speak for song. And those complex sounds are limited to a relatively small group of species that includes songbirds, gibbons and bats.
And bowheads' sounds are some of the most intricate of all the creatures in kingdom Animalia, including their much ballyhooed singing cousins, humpback whales.
The best comparison to the song of the bowhead whale, Stafford told The Washington Post, is a jazz musician, riffing on the fly.
We've largely neglected listening to the 70 percent of our globe that is ocean, Stafford said. That's partly because of the obvious difficulties of obtaining scientifically sound observations in the depths, but also because of the highly visual way that human beings perceive the world.
"We humans, most of us are visual animals. We use our eyes to navigate the world," Stafford said. "Underwater, light doesn't travel very far. Chemical cues don't travel very far. But sound transmits really well underwater — much better than it does over air. You can listen over great distances. Sound is really the way animals are going to navigate and find food and find mates."
That is, by the way, what Stafford believes the complex whales songs are all about: finding mates.
That's because the sounds are at their peak during the mating season, which stretches from November to April.
"We think it's a male reproductive display," she said, adding that humpback whales sing for similar reasons. "This can work one of two ways. Either it's male-male — it's a James Corden (rap) battle, to see who is the most dominant. But it also might be something that females might be listening in to."
During the times of the year when whales aren't searching for a mate, Stafford said, they don't make many sounds. During mating season, the papers said, "bowhead whale songs were detected 24 (hours) per day, throughout most of the winter, every year."
The analysis comes from years of study in the Fram Strait, a deepwater passage on the east coast of Iceland that connects the Arctic Ocean to the Greenland Sea.
A pilot study from 2008 to 2009 found dozens of whales and offered promising insights into the sounds they were making.
According to the Independent, the population of whales that frequents the Fram Strait is endangered. Commercial whalers almost wiped them out in the 17th century, in part because their slow cruising speeds made them easy targets.
But Stafford and the other oceanographers were particularly interested in the sounds they made — and needed more data. So they dropped another set of hydrophones into the water from 2010 to 2014, then listened to the sounds they recorded.
"When we heard, it was astonishing," Stafford said in a news release put out by the University of Washington.
Before, it was thought that bowhead whales were very similar to their humpback cousins, which are widely studied in breeding grounds near Mexico and Hawaii.
"With humpback whales, all the males in the same population may sing the same song, more or less. There are changes, but everybody adopts those changes," Stafford said. "With bowhead whales, there don't appear to be any rules. That's from my human perspective. There may be rules that all the whales understand.
"Both of these whales are complex singers. As far as we know, they're the only two whales in the whale world who sing complex songs," she told The Post. "But they're two sides of the same coin. It's jazz, and it's classical. There's Beyoncé, and then there's the church choir."
Still, she concedes, there are many things researchers don't know. It's unclear whether only males sing, or whether they're capable of sharing the songs with others in the same species.
Most importantly, she said, no one knows why the whales are constantly changing their tunes.
Other researchers are trying to place radio tags on bowhead whales, and acoustic monitoring technology evolves all the time, but Stafford saidwe may never know some of the answers.
For now, the song study adds to our understanding of what she called "superlative" animals that can live 200 years, have some of the thickest blubber on the planet and can break through ice a foot-and-a-half thick to take a breath.
"And you think: They've evolved to do all these amazing things. I don't know why they do this remarkable singing, but there must be a reason."