Humpback hit parade is swimming round the Cape
Two whale populations are picking up song ideas from each other, scientists have shown
Scientists who spent five years listening to humpback whales singing on either side of Africa discovered that they seemed to be picking up musical ideas from each other.
Whales off Gabon and Madagascar incorporated each other’s phrases and themes into their latest songs, suggesting popular whale music is being carried around the Cape of Good Hope by males in the two populations.
The research, reported in Royal Society Open Science, found that humpbacks in the South Atlantic and Indian oceans sing similar song types, but the amount of similarity differs across years.
This suggests that males from these two populations come into contact at some point in the year and learn songs from each other.
“Song sharing between populations tends to happen more in the northern hemisphere, where there are fewer physical barriers to movement of individuals between populations on the breeding grounds,” said Melinda Rekdahl, of the Wildlife Conservation Society, who led the study.
Male humpbacks sing complex compositions consisting of moans, cries and other vocalisations called song units. These are combined into phrases which are repeated to form themes. Different themes are produced in a sequence to form a song cycle which is repeated for hours or days.
For the most part, all males within the same population sing the same song type, which is maintained despite continual evolution or change to the song leading to seasonal “hit songs”. Some song learning can occur between populations that are in close proximity and may be able to hear the other population’s song.
Rekdahl’s team transcribed more than 1,500 individual sounds that were recorded off Gabon and Madagascar between 2001 and 2005, and over time they detected shared phrases and themes in both populations.
At the beginning of the study, whale populations in both locations shared five themes. By 2003, the song sung by whales in Gabon became more elaborate than their counterparts in Madagascar.
In 2004, both population song types shared the same themes, with the whales off Gabon singing three additional themes. By 2005, songs on both sides of Africa were largely similar.
Howard Rosenbaum, director of the WCS ocean giants programme, said: “Studies such as this one are an important means of understanding connectivity between different whale populations and how they move between different seascapes.
“Insights on how different populations interact with one another and the factors that drive the movements of these animals can lead to more effective plans for conservation.”