Underwater Compositions: Song Sharing Between Southern Ocean Humpback Whales
Imagine a world where sight is limited by the extreme scattering of photons and smell is ineffective due to lethargic diffusion of molecules slowed by the density of water. In these conditions both sight and smell are limited. These conditions characterize, among other things, the ocean, where large sea mammals rely mostly on sound to communicate. The speed of sound is four times greater in water than in air at sea level. Male humpback whales have been observed communicating via ever-changing patterns of vocalization, which scientists have termed ‘song’. These whales compose their songs for the purposes of breeding, learning new songs as they come in contact with fellow crooners. Exactly how and when humpback whales learn these songs, however, remains a larger mystery.
To dive more deeply into the nebulous realms of humpback whale song sharing, researchers of a recent PLOS ONE study recorded instances of humpback whale song in the Southern Ocean.
Humpback whale song is identifiable because of its intricate pattern of structure. Songs are composed of multiple sound types, for example, as these researchers suggest, ‘ascending cry,’ ‘moan,’ and ‘purr’. When units come together to form a pattern, these units form a phrase. Phrases repeated become a theme, and themes sung in a particular order compose a song. Researchers recorded these compositions by deploying radio-linked sonobuoys, which transmit underwater sound, and then digitized the recordings.
Here is an example of song recorded off the coast of New Caledonia in 2010:
Recordings, like the one above, reveal a possible link between three distinct breeding populations (marked D, E, and F on the map below) off the shores of eastern Australia and the island to the east of New Caledonia with a shared feeding ground in Antarctica (Area V).
In early 2010, the researchers identified four songs near Antarctica that matched themes from eastern Australia in 2009. By July, 2010, all four songs were then also identified in the group from New Caledonia. The themes recognized in New Caledonia in 2010 were entirely different than the themes of 2009, suggesting a movement of new songs eastward from eastern Australia to New Caledonia.
Consequently, the shared feeding grounds in Antarctica used by both the eastern Australia and New Caledonia groups in early 2010 may be the point at which these populations’ songs diverged.
By capturing sonobuoy recordings near feeding grounds off the Balleny Islands, researchers recorded the first instances of humpback whale song in Area V of Antarctica.
In addition, the inclusion of feeding grounds into the dynamic pattern of humpback whale song sharing helps shed new light on overall patterns of song learning and transmission from one breeding group to another.
Sound recording off the Balleny Islands near Antarctica, however, is challenging, and the sample of whale singers from this area remains relatively small. Regardless, the song documented here suggests Antarctica (Area V) as an emerging location for future study, and highlights the importance of feeding grounds in the transmission of humpback whale song. Through a better understanding of how and where these dynamic compositions radiate across the Southern Ocean, we can begin to understand humpback whale population connectivity and one of the best examples of non-human, large-scale learning demonstrated throughout the Southern Hemisphere.
To listen to more of the whale song recorded by these researchers, check out the Supporting Information of their article. For more on humpback whales, check out these PLOS ONE papers.
Citation: Garland EC, Gedamke J, Rekdahl ML, Noad MJ, Garrigue C, et al. (2013) Humpback Whale Song on the Southern Ocean Feeding Grounds: Implications for Cultural Transmission. PLoS ONE 8(11): e79422. doi:10.1371/journal.pone.0079422
Images and Acoustic Files:
Image 1: Humpback Whale Tail by Natalie Tapson
Acoustic File: doi:10.1371/journal.pone.0079422
Image 2: doi:10.1371/journal.pone.0079422
Image 3: doi:10.1371/journal.pone.0079422