The Whale Album: Why Do Humpbacks 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 not just whistling in the water, but 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.
Birds may broadcast their social hierarchy among song-sharing populations by allowing the dominant bird to pick the playlist and patterns. But how and why whales pass song fragments across hundreds of miles, and to thousands of animals, is far more mysterious.
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 York-based 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 to 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.
文／Karen Weintraub 譯／張江寧