Image: National Marine Fisheries Service
When visiting their breeding grounds, male humpback whales (right) do not swim in silence. Rather, they sing. The tune they carry depends on where they live: populations within an ocean basin sing similar songs, but populations in different ocean basins generally sing different songs. All males in a population, however, produce the same song, which changes over time. Previous studies of whale songs had suggested that such change occurs on an evolutionary scale--that is, gradually. But in this week's issue of the journal Nature, researchers describe revolutionary song change in a population of whales in the Pacific Ocean off Australia's east coast. The radical nature of this transformation, they report, "is unprecedented in animal cultural vocal traditions and suggests that novelty may stimulate change in humpback whale songs."
Michael J. Noad of the University of Sydney and his colleagues eavesdropped on whales off southeast Queensland during migrations between 1995 and 1998, analyzing 1,057 hours of song. (Singing is presumably a form of sexual display, but whether the males are serenading females or warning other males to stay away is not known.) In the first two years the team detected modest, evolutionary change in the tune, but they noted that two of the whales were singing entirely different songs. In 1997 more whales picked up the new song-- most sang either the new song or the old song, but a few produced an intermediate version with themes from both types. By 1998 the researchers heard only the new song. Intriguingly, that song was almost exactly the same as the song of humpbacks traveling along Australia's west coast in 1996. The team thus concludes that a small number of singers from the west coast population must have joined the east coast population, bringing their catchy west coast ditty with them.