Why does the humpback whale sing?
Sometimes a whale just wants to change its tune.
That’s one of the things researchers have learned recently by eavesdropping on whales in several parts of the world and listening for changes in their pattern and pitch. Together, the new studies suggest that whales are constantly evolving a form of communication that we are only beginning to understand.
Most whales and dolphins vocalize, but dolphins and toothed whales mostly make clicking and whistling sounds. Humpbacks, and possibly bowheads, sing complex songs with repeated patterns, said Michael Noad, an associate professor in the Cetacean Ecology and Acoustics Laboratory at the University of Queensland in Australia.
The biggest question is why whales sing at all.
“The thing that always gets me out of bed in the morning is the function of the song,” Noad said. “I find humpback song fascinating from the point of view of how it’s evolved.”
The leading hypothesis is that male humpbacks — only the males sing — are trying to attract females. But they may also switch tunes when another male is nearby, apparently to assess a rival’s size and fitness, said Noad, who was the senior author of one of four new papers on whale songs.
Why the humpbacks’ musical patterns tend to be more complex than those of other whales is also a bit murky. Noad suggested that the development may be the result of “runaway selection.”
Early humpbacks with complex songs were so much more successful at mating that they gained a substantial evolutionary advantage over their brethren with simpler vocalizations. This led to some very large, sometimes very noisy animals.
In one of the new studies, led by scientists at the New Yorkbased Wildlife Conservation Society, researchers tracked humpbacks singing along the east and west coasts of Africa, comparing songs sung by those off the coast of Gabon with those near Madagascar.
The study, published in the journal Royal Society Open Science, confirmed that the two populations interact, noting overlap in their vocalizations. The researchers recorded songs annually from 2001 to 2005 using hand-held hydrophones aboard boats.
“Male humpback whales within a population tend to sing the same song type, but it’s continuously changing and evolving over time,” said Melinda Rekdahl, the study’s first author and a marine conservation scientist with the wildlife society. “It’s thought to be one of the best examples of cultural evolution in the animal kingdom.”
Some animals repeat sounds more than others, some sing “aberrant” tunes, and juveniles may hum jingles altogether different from the adults. Humpbacks also alter their tunes over time.
Two additional recent studies examined how the songs change, seasonally and across years.
In one paper, Jenny Allen, who was a doctoral student with Noad, found an unexpected pattern among humpbacks. Once their songs reach a certain level of complexity, humpbacks drop that tune and pick up a new, simpler one. Her study, the first to quantify the complexity of the songs, was published in Proceedings of the Royal Society B: Biological Sciences.
Assuming that the songs are meant to attract females, “it might be that a brandnew song is a bit sexier than continuing to sing the complicated version of the old song,” said Allen, now a postdoctoral researcher at the University of Queensland and a lecturer at Griffith University in Australia. But “they’re simplifying it to make it easy to learn so much new material all at once.”
In another new paper, researchers at the University of Brest in France found that the pitch of Antarctic blue whale, pygmy blue whale and fin whale vocalizations fell from 2007 to 2016 at various recording sites in the southern Indian Ocean.
Because of a whale’s anatomy, a louder call is higher in pitch, and a quieter one is lower. Essentially, the whales have gotten slightly quieter, said Emmanuelle Leroy, now a research fellow at the University of New South Wales and an author of the new research.
Her team has two hypotheses to explain the drop in pitch across years. With the populations rebounding since the end of commercial whaling, perhaps the whales don’t need their calls to carry as far to be heard by others.
Or perhaps with oceans acidifying because of climate change, the calls are naturally carrying farther, allowing the whales to reduce their volume. The team does not believe the change in pitch is tied directly to human activity.