Humpback whale song hybridizations
Humpback whales don’t just sing songs — they compose with the whales around them, singing a song that evolves over time. It has long been known that their songs progressively change throughout a breeding season and between years. Within a population, all males produce very similar songs at any one time and their songs closely resemble those of surrounding whales much more than their own from previous years or months. As the breeding season progresses all the males within a population must constantly evolve and update their songs to maintain the conformity.
Their songs are hierarchical. Single sounds i.e. units are organised into a phrase, which is then repeated several times characterising a different theme. A song consists of several different themes that are repeated without stopping to form a song session. Songs are not identical and typically vary in the total duration, theme composition and the number of times phrases of specific themes are repeated.
New research on hybrid singers has revealed how these mammals learn and evolve their melodies. By analysing song hybridizations it was revealed that the old and new songs were spliced together in two different ways. The whales either sing part of the original song and part of the new song with a transition between the two song types in a short hybrid phrase, or they splice a whole new theme into their original song from the new song that other whales in the surrounds are beginning to sing. When the whales switch mid-song, it was always during a theme which was similar between the two song types, suggesting that the themes may play a role in helping with social learning.
The themes of the hybrid songs were intact, implying that the whales are likely to learn the songs theme-by-theme like separate verses of a human song. The rate of change of their songs over vast areas of the ocean shows they are constantly changing their songs very quickly. This provides evidence of social learning and cultural transmission whereby information is shared between individuals and populations rather than via genetics.
Although the list of studies involving humpback whale songs is long and extends from 1970, their exact function is still unknown. It is also unknown as to what makes their songs change over time. Perhaps the whales are just changing their songs to be slightly different and then other whales are copying that novelty which others then conform to or perhaps the females are more attracted to males that are able to innovate. The mystery of the majestic humpback whale song continues.
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