Whales learn new tunes at shared Antarctic feeding grounds.
Male humpback whales are known for their complex breeding croons. Their elaborate compositions of moans, shrieks, purrs and whoops rival in complexity those of even the most melodious songbirds.
Within a population of humpbacks, all males sing the same popular song, younger males learning the tune from listening to older troubadours. Humpbacks also like to mix it up a bit, adding and modifying notes and phrases so that a population’s song is constantly evolving.
Whales that are geographically isolated from each other usually have distinct songs. Humpbacks in the Atlantic Ocean, for example, sing a very different tune to those that make their home in the Indian Ocean. Populations in closer proximity often have more similar songs, indicating that whales take some of their musical inspiration from the songs sung by neighboring populations.
How songs are shared between populations has been somewhat of a mystery. It could be that songs are transmitted by males moving from one breeding population to the next. Another hypothesis is that songs are shared along common migratory routes.
In a study published this week in the journal PLoS ONE, an international team of researchers has described how humpback whales share songs in feeding grounds near Antarctica in the Southern Ocean.
The western and central South Pacific is home to five breeding populations of humpback whales. Their breeding sites range from the Great Barrier Reef, which hugs the eastern Australian coast, to the islands of New Caledonia, Tonga, the Cook Islands and the islands of French Polynesia, some 6000 kilometers to the east of the Great Barrier Reef.
Each population spends the winter months breeding and birthing in these warmer waters, before migrating to one of two shared feeding grounds in the Southern Ocean near Antarctica. The summer months spent in these feeding grounds provide the whales with enough food to last them through the following winter.
Most recordings of whale song have been taken at breeding grounds, where the whales are most vocal. But acoustic recordings taken on the Australia–New Zealand Antarctic Whale Expedition in the Southern Ocean in 2010 presented the researchers with a rare opportunity to hear whale song during the summer feeding season.
To determine whether the feeding grounds could be a site where whales from different populations share songs, the researchers compared recordings taken from the Southern Ocean with recordings from breeding sites off the east coast of Australia and in New Caledonia.
Whale songs are composed of notes and phrases in much the same way as our songs. ‘Units’ of sound, akin to our notes, are arranged into patterns (‘phrases’) that are repeated to form a ‘theme.’ Several themes are sung in succession to form a complete song that can last up to 20 minutes.
The researchers analyzed recordings from the three sites, breaking down songs into their component phrases and themes. Four melodic themes, recorded in the Southern Ocean in early 2010 matched themes from the Australian breeding site in 2009 and from New Caledonia in late 2010.
An eastward transmission over time of humpback whale song across the southern Pacific Ocean has previously been observed. This new study, describing whale song in feeding grounds where whale song has not previously been recorded, suggests that feeding grounds could be a key point of transmission for whale song between populations.
The transmission of whale song within a population is one of the clearest examples of cultural learning in a non-human animal. The sharing of songs between populations indicates that whale culture is not limited by breeding group. By gathering recordings from around the globe, the researchers believe that it might be possible to one day map a song’s progression as it circumnavigates the polar waters, passed from one population to the next by its singing bulls.
Reference: Garland EC, Gedamke J, Rekdahl ML, Noad MJ, Garrigue C and Gales N (2013). Humpback whale song on the Southern Ocean feeding grounds: Implications for cultural transmission. PLoS ONE DOI: 10.1371/journal.pone.0079422