Whales sing a new song
Humpback whales from the east coast of Australia have changed their tune thanks to a few visiting whales from the west.
Research published in this week's Nature shows that in less than two years whales in the Pacific Ocean completely swapped their complex and distinctive song for one used by those in the Indian Ocean.
"To our knowledge, such 'cultural revolution' is unknown in the vocal cultural tradition of any other animal," writes Michael J Noad of the University of Sydney and colleagues.
Male humpbacks are thought to 'sing' as a form of sexual display. Their song patterns depend on where they live, with populations of whales in different ocean basins have quite distinct songs.
The song shared by all males in the same population evolves slowly over time, as bird song has been known to, however a relatively sudden swapping of a traditional for a foreign song is unexpected.
Noad and fellow researchers recorded whales off southeast Queensland during their northward and southward migrations between 1995 and 1998. They used hydrophones suspended from radio-linked buoys and small boats to record 1,057 hours of song.
In 1995 and 1996, two singers out of 82 were singing a new, complementary different song.
In 1997 the new song was becoming more popular, and three singers used an intermediate song containing themes from both types.
By the end of the 1997 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 different. However, it just so happened that there was a movement of a small number of singers between populations in 1996.
Changes in whale song are termed 'cultural' evolution or revolution because they are due to the learning of a vocal behavioural pattern and not to a mass influx of immigrants.