0758 GMT October 19, 2018
While the songs of humpback whales have long received the most attention, it turns out that their baleen cousins could have a far greater repertoire, according to bbc.com.
A study of a bowhead population near Svalbard has shown that their musical calls may be as varied as those of songbirds.
This would make them unique among whale populations, and possibly even mammals.
Over the course of three years, the whales of the Spitsbergen population produced 184 unique song types. The vocalizations were detected 24 hours a day throughout most of the winter each year.
Prof. Kate Stafford, lead author of the study published in the Proceedings of the Royal Society, said, "The alphabet for the bowhead has got thousands of letters as far as we can tell.
"I really think of humpback whale songs as being like classical music. Very ordered.
“They might last 20-30 minutes. An individual [bowhead] song might only be 45 seconds to 2 minutes long, but they'll repeat that song over and over again.”
Humpback whales are known to sing similar songs across a single season, but for bowheads, song types only lasted a few hours or days before changing.
These complex songs are unusual, as most mammals have distinct, repetitive calls which do not vary.
Although less is known about bowhead populations, the authors think it likely that males do the singing during the breeding season.
With the ability to break through up to half a meter of ice, and a potential lifespan of 200 years, bowheads can seem quite formidable.
Yet their blubber, the thickest of any whale species, led to the Spitsbergen population being commercially hunted as early as the 1600s.
This reduction in their numbers, and the harsh environment of their natural habitat under the ice, has meant that they are poorly studied and remain somewhat mysterious.
Stafford said, “Other bowhead groups, such as the Western Arctic population, are better understood thanks to the knowledge of native Alaskans.”
Yet she added that overall we know ‘relatively little’ about the species.
It is not yet known whether individual bowheads sing the same song for a lifetime, or if they change from season to season.
The reason for the diversity of calls in this one population hasn't been determined either.
It wasn't possible to count the Spitsbergen group using the hydrophone recordings, but previous work in the region had put the population at a minimum of 343 whales.
What remains, said Stafford, is to acoustically track individuals and learn more about who is vocalizing, and why.
She added, "It's a mystery that's going to be really hard to solve.
“But being able to eavesdrop under the ice in this remote place... It's pretty remarkable."