Humpbacks have picked up a catchy tune sung by immigrants from a distant ocean.
The song patterns of humpback whales (Megaptera novaeangliae) depend on where they live, with populations inhabiting different ocean basins normally singing quite distinct songs. Here we record a unique and radical song change in the song of humpback whales in the Pacific Ocean off the Australian east coast. Their song was replaced rapidly and completely by the song of the Australian west coast population from the Indian Ocean, apparently as a result of the introduction of only a small number of 'foreign' singers. Such a revolutionary change is unprecedented in animal cultural vocal traditions and suggests that novelty may stimulate change in humpback whale songs.
Male humpback whales sing while migrating to and from their breeding grounds, and when they are at the grounds themselves1,2,3. Song is thought to be a form of sexual display, but it is not known whether its main purpose is to repel other males or to attract females2,4. All males in a population produce the same song, which changes through time2,3,5, and all singers maintain the changes, implying that there is a cultural transmission and evolution as in some bird songs6. Songs across an ocean basin are broadly similar — differences increase with distance — but populations in different oceans separated by continents have apparently unrelated songs3,7.
In the austral winter and spring, humpback whales are found along the east coast of Australia3,8, calving and mating in the waters of the Great Barrier Reef. Using hydrophones suspended from radio-linked buoys and small boats, we recorded humpback whale songs off southeast Queensland during northward and southward migrations between 1995 and 1998, from which 1,057 hours of song were analysed. In 1995 and 1996, the song pattern changed slightly in an evolutionary fashion. But two singers out of 82 were singing a new, completely different song (Fig. 1). In 1997, the new song became more common. Most of the 112 singers produced either the old or the new song, but three used an intermediate song containing themes from both types. By the end of the 1997 southward migration, almost all males had switched songs, and in 1998 only the new song was heard.
The new song was nearly identical to the song of humpback whales migrating along the west coast of Australia in 1996. West and east coast songs are usually very different3 and there is only a small amount of interchange between these populations8,9. The very low incidence of the new song in 1996 and the fact that the songs of the two populations evolved independently after 1996 is consistent with the new song being introduced by movement of a small number of singers between populations in 1996.
Humpback whale song shows similarities to song in some birds, particularly the Panamanian yellow-rumped cacique (Cacicus cela vitellinus)10 and village indigo bird (Vidua chalybeata)11, in which song repertoires are colony-specific and all individuals have similar repertoires which change with time. But there are no examples of radical song replacement initiated by a small number of immigrant individuals in these or any other species of songbird.
The process of change in humpback whale song and bird song has been classified as 'cultural evolution', whereby changes in songs are passed among individuals by learning and accumulate over time6. The changes we describe in the song of the humpback whales off the east coast of Australia were cultural in that they were due to the learning of a vocal behavioural pattern and not to a mass influx of immigrants. But the rapid and complete replacement of a complex song over a period of less than two years is revolutionary rather than evolutionary, and suggests that novelty drives changes in humpback whale song. To our knowledge, such 'cultural revolution' is unknown in the vocal cultural tradition of any other animal.
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