In the pitch-black waters beneath the Arctic ice, bowhead whales get funky. A small population of endangered bowheads belt an unusually varied repertoire of songs, which grows more diverse during mating season.
Hunted to near extinction in the 1600s, these fire truck–sized mammals now number in the 300s in the frigid waters around the Svalbard archipelago in Norway. Underwater audio recorders captured the whales singing 184 acoustically distinct songs from October to April in 2010 through 2014.
On the bowhead charts, a song’s popularity is fleeting. Most recorded songs were heard for less than 100 hours total, although one song registered over 730 hours total. Some songs appeared in more than one month, but none repeated annually. December and January, likely the height of breeding season, saw a wider array of new bowhead songs than other months, researchers report in the April Biology Letters. Hearing a more distinct mixtape may play a role in enticing a female to mate.
A hot cetacean band
The Spitzbergen bowhead whale songbook contains a wide variety of tunes, and some stick around on the charts longer than others. Here each bubble corresponds to one of the 184 songs recorded by researchers from 2010 to 2014. The size of the bubble corresponds to the number of hours it was sung. Click on any of the dark green bubbles to hear that whale’s song.
Source: K.M. Stafford et al/Biology Letters 2018
Groups of humpback whales don’t change their tunes much in a given year, compared with bowheads. Only a few songbird species boast similar diversity.
While some bowhead songs sound like haunting melodies stereotypical of humpback whale songs, other bowhead songs are just plain weird. “Sometimes it sounds like animals having a party in a barn,” says Kit Kovacs, a biologist with the Norwegian Polar Institute in Tromsø. “Other times it’s almost extraterrestrial.” It’s impossible to link a specific song to an individual whale, so whether whales replace old songs with new ones or if some individuals simply stopped singing for a bit remains unclear.
These songs differ from run-of-the-mill vocalizations. Bowheads do emit simple calls that are sometimes repeated out into the depths. But songs are marked by acoustic patterns and notes, and can go on for hours. “They are so different. It’s difficult to recognize all of these as coming from the same species,” Kovacs says.
Keeping it fresh
Researchers found that bowhead whales are constantly introducing new songs into their repertoire each month. December and January — the time researchers suspect is the peak of mating season — saw the highest numbers of new songs introduced from 2010 to 2014.
Normally, animals sing as a form of species identification. That’s why humpback groups all sing basically the same song, helping to ensure that they’re courting the correct species. Because bowheads are the only baleen whales that reside that far north, checking ID may be less of an issue for them.
The bowheads also breach the traditional cetacean trade-off between serenading females and knocking them up. Bowheads breed through the winter months — when it’s dark 24 hours a day. A handful of males surround a female and simultaneously try to mate with her. Usually the male with the most sperm wins the day. Other species, including whales, opt to invest either in singing ability or sperm count (SN Online: 10/22/15), but bowheads put their effort into both. It’s an odd anomaly, Kovacs says. “If you’re going to sing all of these amazing songs, then why do you need all that sperm?”
Determining whether bowhead whales across the Arctic practice similar song improvisation requires more data. For now, the motivations behind the bizarre melodies of the Svalbard whales are even more enigmatic than those of human musical improvisers. “Even experimental jazz isn’t as weird as these bowheads,” Kovacs says.