Science

The song of humpback whales can “spread” 8000 km (throughout the South Pacific)

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Whale song has long been recognized by the scientific community as part of cetacean culture, defining distinct groups of individuals. Recently, a team of researchers discovered that songs created by humpback whales in parts of the Pacific off Australia are imitated by whales near the equator in just a few years. This discovery of cultural exchange will help to understand the mechanisms underlying the study of these songs and the evolution of communication.

Humpback whales are cetaceans that measure about fifteen meters and about thirty tons. They are a favorite subject of study because of their complex songs that change from year to year, and also because of their long migration across the Pacific. In summer, they feed in areas close to the poles, and in winter they come to breed in areas with a temperate climate.

In humpback whales, it is the males who sing very stereotypically, repeating themselves and developing. Females and young have much shorter and less complex songs that make up social songs.

Indeed, the song of males is organized in a hierarchy. At the first level, each vocalization (defined as the shortest continuous sound) is called a “one”. Several combined units form a chain of units called a “supply”. Several repeating phrases create a “theme”, and several themes performed in a certain order form a “song”, which usually lasts from 5 to 30 minutes. Repeated songs are called “song sessions”, which can last several hours.

Not to mention that these songs are evolving every year. They are produced mainly in breeding areas, but also along migratory routes. The function of the song remains controversial, although some scientists believe that it plays an important role in male reproductive success.

It should be noted that in the South Pacific region, the change in the song of the humpback whale can occur in two ways: gradual cultural evolution and cultural “revolution”. The latter describes the rapid replacement of one song type by an entirely new type introduced by neighboring populations, although the underlying mechanisms underlying this phenomenon remain unclear. These songs seem to spread in one direction from eastern Australia to French Polynesia.

Faced with such vocal communication from distant populations of humpback whales, scientists want to know how far a song can be transmitted east. Recently, a research team made up of staff from the University of St. Andrews, the University of San Francisco Quito and the Acoustic Ecology Program of the CETACEA Ecuador project discovered that the songs emitted by humpback whales off the coast of eastern Australia are imitated by the whales. from the equator, almost 8000 km. Their work has been published in the Royal Society Open Science.

Songs spreading along migratory routes

This study follows a 2019 discovery by the same team at St. Andrew’s University that showed that humpback whales can learn new songs by moving along a common migration route.

Thus, it has been suggested that a location in the western South Pacific, the Kermadec Islands, served as a stopover for humpback whales from several populations during their southward migration. Similarities in song themes linked the Kermadec Islands to several wintering grounds and provided early indications of where cultural transmission between acoustically isolated winter spawning populations might occur.

Whale songs were already known to be transmitted east across the South Pacific, traveling through breeding populations from Australia to French Polynesia in a series of “revolutions” spanning only three years and crossing the ocean in waves. A 2019 study shows that migratory convergence appears to facilitate the study of whale songs, as well as the transmission of songs to the east, and possibly cultural convergence.

Dr Ellen Garland of the University of St. Andrews said in a statement: “Male humpback whales perform complex and culturally transmitted songs. Our research has shown that the migration patterns of humpback whales appear to be written into their songs. We found similarities between the songs of the Kermadec Islands and the songs of some wintering areas.

Cultural exchange in the South Pacific

This study provides the first evidence of cultural transmission of songs eastward from the central South Pacific breeding population of French Polynesia to the eastern South Pacific breeding population of Ecuador.

Specifically, from 2016 to 2018, the team recorded humpback whale songs using a stand-alone SoundTrap recorder in various locations in the Pacific Ocean. They then performed two similarity analyses, calculations that measure how similar two songs are to different sounds made by whales in two regions.

Then they found that two groups (one in French Polynesia, the other near the equator) had their own songs from 2016 to 2017, and in 2018 they were recorded with the same song, more precisely, three themes were common to the population.

Spectrograms of three song themes common to bands from French Polynesia (FP, left) and Ecuador (EC, right). © 2022 EU Garland et al.

Surprisingly, this demonstrates that humpback whales are vocally connected across the Pacific Ocean. The transfer of songs between French Polynesia and Ecuador is likely facilitated by overlapping feeding areas around the western Antarctic Peninsula. This study expands our understanding of the extent of cultural transmission among humpback whale populations in the South Pacific and helps uncover the mechanisms underlying song learning.

However, further research is needed to confirm whether humpback whale song cycles from French Polynesia to Ecuador regularly spread, and if so, at what intervals. In addition, to assess the extent of this cultural phenomenon, future research should determine whether songs continue to travel eastward from the Equator (Eastern South Pacific) to Brazil (Western South Atlantic) and beyond across the southern hemisphere.

In conclusion, the authors believe that understanding this cultural phenomenon will provide valuable comparative information about the evolution of complex communication, including the evolution of language and human culture. As with humans, migration patterns are recorded in the songs of humpback whales.

Royal Society Open Science.

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