Scientists have recorded 184 elaborate, very different bowhead whale songs in a bowhead subpopulation living east of Greenland. This makes it the largest set of bowhead whale song recordings ever.

The bowhead’s vocal repertoire is rivaled only by a few species of songbirds, researchers say.

But why these whales have so many different song types and why they change their songs each year is still a mystery.

Under the Arctic ice, a mysterious concert plays out each winter.

Bowhead whales (Balaena mysticetus) living east of Greenland break into a wide range of complex, intricate songs, showcasing a new set of musical notes every year.

Kate Stafford, an oceanographer at the University of Washington, and her colleagues first heard these bowhead whales singing in 2007. The following year, in a preliminary study, Stafford recorded more than 60 unique whale songs from October 2008 to April 2009.

“We were hoping when we put the hydrophone out that we might hear a few sounds,” Stafford said in a statement, referring to the study published in 2012. “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.”

Stafford and her team expanded on the study by deploying hydrophones, or underwater microphones, in the Fram Strait between Greenland and the Svalbard archipelago in the Arctic from 2010 to 2014. During this period, they recorded 184 different bowhead whale songs, making it the largest set of bowhead song recordings ever, the researchers report in a new study published in Biology Letters.

Some song types lasted only a few hours or days, the researchers found. Others persisted over months. But the whales never seemed to repeat their songs between the years.

“If humpback whale song is like classical music, bowheads are jazz,” Stafford said. “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.”

Bowhead whale song recorded in Fram Strait on Feb. 11, 2013. Kate Stafford/University of Washington

Bowhead whale song recorded in Fram Strait on Dec. 30, 2013. Kate Stafford/University of Washington

Such complex songs are rare among mammals, the authors write. Many mammals have short, repetitive calls. But only some mammals sing, that is, produce complex, distinct musical phrases that need to be learned. Such songs have been recorded in a few mammals like some bats, gibbons, mice, rock hyraxes, and humpback and bowhead whales, the authors add.

The bowhead’s vocal repertoire, however, is rivaled only by a few species of songbirds, they say. The researchers say bowhead whales might be using their songs to navigate, find food and communicate. But why they have so many different song types and why they change their songs each year is still a mystery. Further monitoring using radio tags might be able to answer these questions, the researchers say.

“Bowhead whales do this behavior in the winter, during 24-hour darkness of the polar winter, in 95 to 100 percent sea ice cover. So this is not something that’s easy to figure out,” Stafford said. “We would never have known about this without new acoustic monitoring technology.”

The bowhead whales spend all their lives in the icy waters of the Arctic. Their global populations seem to be increasing, according to the IUCN Red List. But the subpopulation that Stafford and her team monitored is listed as critically endangered because the whales were hunted to near extinction by commercial whaling from the 1600s to the early 1900s. The subpopulation is currently estimated to have about 200 individuals.

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