Beneath the ice, a species of whale sings up a jazz storm all through the months-long High Arctic night, according to research published in the British Royal Society’s journal Biology Letters.
While there are plenty of bird species that give voice to complex songs, mammals are a comparatively mute bunch. Most mammalian calls are simple and repetitive, lacking the diversity, phrasing and themes that characterise true song.
Only a handful of produce vocal displays approaching the complexity of birdsong: some bats, gibbons, mice, rock hyraxes (Procavia capensis, little critters that look like tubby rodents but are closely related to elephants), and two whale species: humpback and bowhead.
The humpback (Megaptera novaeangliae) is a well understood species and its capacity for song has been extensively studied. From year to year its songs vary, but have a strong similarity across the whole population. Humpback songs “are composed of a hierarchy from units to sub-phrases to phrases to themes” write the authors of the new paper.
The bowhead (Balaena mysticetus) is the only resident baleen whale in the High Arctic and is far less understood. Lead author Kate Stafford, an oceanographer at the University of Washington’s Applied Physics Laboratory, US, has published previous research based on five months of audio recordings of bowhead song captured using underwater microphones, called hydrophones.
Now she and three Norwegian colleagues report the findings of a much more extensive set of hydrophone recordings of a population of bowhead whales found in the Fram Strait, between eastern Greenland and the Norwegian archipelago of Svalbard, sometimes also known as Spitsbergen.
It turns out that the Spitsbergen bowheads are passionate singers with a constantly changing repertoire that exhibits a stunning, and unpredicted, diversity.
“If humpback whale song is like classical music, bowheads are jazz,” says Stafford. “The sound is more free-form. 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.”
While Stafford and her team pose some explanations, they remain little more than candidate hypotheses: the Spitsbergen whales might have come into contact with other bowhead populations due to vanishing sea ice, or they may be the remnant of a population that were nearly hunted to extinction in the 1600s, causing small-population dynamics to diversify their singing.
“Why are they changing their songs so much?” Stafford ponders. “In terms of behavioral ecology, it’s this great mystery. I don’t know why they do this remarkable singing, but there must be a reason.”