The humpback whales swimming off eastern Australia have pulled off a musical revolution, completely changing their song within a year.
Normally they鈥檒l add a new passage here, drop an old part there. But, according to Mike Noad of the University of Sydney, they have completely abandoned their old refrain and taken up a new one.
鈥淣ormally it takes several years to get substantial change in a song and you can trace its evolution. This was nothing short of a revolution, a complete takeover,鈥� says Noad.
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The new song appears to have been imported by infiltrating humpbacks from the Indian Ocean.
Love song or war cry?
Male humpbacks sing as they migrate between their feeding grounds and the waters where they breed. No one is certain whether the songs are to warn off other males or to attract females but all the males in a population stick to the same song.
Populations from neighbouring waters share some musical themes, but those from separate oceans sing completely different songs. The songs change with time, but they usually evolve slowly.
Noad has been eavesdropping on the humpbacks that mate and calve around the Great Barrier Reef since 1995. The first year, all the whales sang the same song. But in 1996, Noad heard something odd. Of the 82 singers he recorded, two were singing a bizarre new song.
By the end of 1997, almost all the males had ditched the old song and were singing the new. When Noad first heard the strange recordings he wasn鈥檛 sure what was going on. 鈥淏ut then someone sent me a tape of whales from Western Australia. It was instantly obvious that it was the same song. I even pulled the tape out to check I鈥檇 put the right one in.鈥�
No mixing
Evidence from old whaling tags and from modern genetic studies suggests that there is little intermingling of humpback populations, so large-scale immigration seemed an improbable explanation for the takeover.
Noad believes a handful of western whales strayed into the Pacific, and the resident whales simply found their song compelling. It was the song that had taken over, not a new group of whales.
鈥淲e have no idea why they would move across,鈥� he says. 鈥淢aybe the krill they were feeding on moved eastward and they followed it. Then, when they headed north again to breed they ended up on the wrong side of Australia.鈥�
But what was it about the new song that was so attractive? 鈥淲hy singers change the pattern of their song is one of the great mysteries,鈥� says Noad. He suspects that the whales are stimulated by novelty and that it was the very strangeness of the song that made it attractive. 鈥淲e think that maybe whales crave change.鈥�
More at: Nature (vol 408, p 537)