04 October 2019

Tracking Whale Songs

It’s the 23rd century. To save Earth from an alien probe, Admiral James T. Kirk and his crew go back in time to 1986 to retrieve the only beings that can communicate with the probe--humpback whales, now extinct. (Star Trek IV: The Voyage Home)

Welcome back. An international team led by a researcher with the UK’s University of St. Andrews published a study that reminded me of that movie. The reminder is a bit of a stretch since the only connection is the humpback whale song.

Humpback Whale Songs and Transmission
Vocal traditions and vocal learning provide a foundation for studying culture and its transmission whether by humans or whales.

Humpback whale and diver (from
Male humpback whales (Megaptera novaeangliae) perform complex, hierarchically structured vocalizations. A sequence of sounds termed “units” comprises a “phrase,” phrases are repeated to form a “theme,” a few themes are sung in a set order to form a “song” and different versions of a song that contain different themes are called “song types.”

Although songs are constantly evolving, most males within a humpback whale group will converge on a single song type during any particular winter breeding season. Songs are also transmitted between groups. The rapid adoption of a new song from a neighboring group is a striking example of large-scale, horizontal cultural transmission.

Documenting South Pacific Whale Songs
To investigate humpback whale song transmission in the South Pacific, the researchers recorded whale songs during the same breeding season at sites spanning some 6,000 kilometers (3,730 miles). These included the Kermadec Islands, a migratory stopover, and six wintering grounds--eastern Australia, New Caledonia, Tonga, Niue, the Cook Islands and French Polynesia.

South Pacific study area showing Kermadec Islands (near center) and six wintering grounds (L to R: eastern Australia, New Caledonia, Tonga, Niue, the Cook Islands and French Polynesia) (from royalsocietypublishing.org/doi/10.1098/rsos.190337).
All humpback whale song recordings were analyzed as spectrograms, which display the vocalization’s amplitude at different frequencies versus time. (In two dimensions, the y-axis is usually signal frequency, the x-axis is time, and signal amplitude is shown as the intensity or color.)

Three song types were identified in recordings from 52 “singers” at the six wintering grounds. One was dominant in the central Pacific (Cook Islands and French Polynesia), the second was the most prevalent in the west (New Caledonia, Tonga and Niue) and the third was only recorded in eastern Australia.

Example spectrograms of humpback whale song type 1 (top), 2 (middle) and 3 (bottom) (from royalsocietypublishing.org/doi/10.1098/rsos.190337).
Migratory Stopover Song Transfers
Given that whales from different groups pass the Kermadecs at the same time during their southward migration, there is ample opportunity for song learning and transmission across the South Pacific.

When songs from 39 singers recorded at the Kermadecs were compared to those of the 52 singers from the six wintering grounds, the Kermadec songs could be matched to New Caledonia, Tonga, Niue and the Cook Islands. The matches were supported by genetic and photographic data. The comparative analysis also suggested that singers from French Polynesia and eastern Australia did not stop at the Kermadecs.

Of particular interest was one “hybrid singer” from the Kermadecs that sang themes drawn from two song types. This would be consistent with song learning on migration.

Wrap Up
The researchers conclude that the similarities in songs from the Kermadec Islands and multiple wintering grounds suggest the Kermadec migratory stopover and presumably other migratory stopovers are locations of cultural transmission, active song learning and the potential for cultural convergence after group isolation at the wintering grounds. As with human correlations between genes, communication and migration, humpback whale migratory patterns are written into their songs.

Thanks for stopping by.

Star Trek IV: The Voyage Home: www.imdb.com/title/tt0092007/
Study of humpback whale song transmission in Royal Society Open Science journal: royalsocietypublishing.org/doi/10.1098/rsos.190337
Article on study on New Scientist website: www.newscientist.com/article/2215121-we-can-tell-where-a-whale-has-travelled-from-the-themes-in-its-song/
Examples of humpback whale song types from study’s supplemental material:
Song Type 2 (Niue et al.) - rsos190337supp6.mp3
Song Type 3 (eastern Australia) - rsos190337supp7.mp3

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