One of the most remarkable things about our species is how quickly human culture is able to change. New words can spread from one continent to another. Technologies like cell phones and drones transform the way people live around the world.
We now learn that humpbacks, or humpback whales, have their own high-speed, long-range cultural evolution, and they don’t need internet or satellites for that.
In a study published Tuesday, scientists found that humpback calls are easily transmitted from one population of whales to another across the Pacific Ocean. A corner can take only two years to travel thousands of kilometers.
Ellen Garland, a marine biologist at the University of St. Andrews, Scotland, is one of the study’s authors. She said she was stunned to discover whales in Australia transmitting their calls to other whales in French Polynesia, which in turn transmitted their calls to whales in Ecuador.
“Today half the globe is vocally connected by whales,” she said. “It’s amazing.”
It is even possible that the chants run through the entire Southern Hemisphere. Preliminary studies by other scientists are revealing whales in the Atlantic Ocean learning songs from whales in the eastern Pacific.
Each humpback population spends the winter in the same breeding grounds. There the males sing underwater songs at high volume, which can last up to half an hour. Males at the same breeding site sing an almost identical tune. And from one year to the next, the song of the population gradually evolves until it becomes a new melody.
Garland and other researchers have brought to light a complex structure present in these chants, something that resembles a language. Whales combine short sounds, which scientists call units, to form sentences. Then combine the phrases to form themes. And each corner is composed of several themes.
Male humpbacks will sometimes change a unit in their song. Every now and then they add a new phrase or delete a theme. The other males then copy what was done. These beautifying modifications cause the population’s song to gradually evolve, resulting in drastically different melodies from one population to another.
Marine biologist Michael Noad of the University of Queensland found that the song of a whale population can occasionally undergo a large and sudden change. In 1996 he and his colleagues noticed that a male whale off the east coast of Australia had given up on the local song and started singing a tune that corresponded to one previously sung on the west coast of the country.
Within two years, every male on the east coast was singing this song. Noad’s study was the first to find this kind of cultural revolution taking place in any animal species.
Garland did her PhD with Noad in the early 2000s, recording humpback calls in breeding grounds further east in the Pacific Ocean. When she compared the chants, she found the same pattern spotted by Noad: songs sung in eastern Australia appeared two years later in French Polynesia, 9,500 kilometers away.
After publishing this initial finding, in 2011, Garland continued to record humpback songs at the same breeding sites. And she was curious to know if the chants were spreading eastward across the Pacific.
An opportunity to discover this came when marine biologists Judith Denkinger and Javier Oña of the University of San Francisco de Quito in Ecuador offered to collaborate. They study humpbacks that breed off the coast of Ecuador.
For their new study, Denkinger and Oña recorded humpbacks between 2016 and 2018. In the same period, Michael Poole, a marine biologist with the Marine Mammal Research Program on the island of Moorea, French Polynesia, recorded whale calls there.
Scientists set up anchored underwater microphones that could record the sounds of passing whales. In addition, they followed the whales by boat, plunging microphones into the water to capture their calls.
In 2016 and 2017, the two whale populations had distinctly different songs. But in 2018 there was a revolution: the whales of Ecuador were including French Polynesian themes in their songs.
The scientists reported their findings Tuesday in the journal Royal Society Open Science.
Elena Schall, a postdoctoral researcher at the Alfred Wegener Institute in Bremerhaven, Germany, and not involved in the study, said they have seen some similar patterns in the Atlantic Ocean. Humpback whales off Brazil and South Africa have been adopting previously recorded themes off the coast of Ecuador.
It is conceivable, Schall said, that the songs travel across the southern hemisphere. “It’s possible, but data on the Indian Ocean is lacking,” she said. “I think this will definitely be the next step, if we can find enough data for comparisons.”
Garland and Schall agree that the songs are likely spreading as whales leave their breeding grounds and migrate to feeding regions near Antarctica. During this trip, a male humpback may end up swimming alongside males from another group. When these other males hear the song radically different from the first, they may borrow some themes or even steal the entire song. And they will continue to sing the new song when they return to their breeding sites.
As to why the songs move mainly from west to east, Garland suggested that it might be due to the enormous size of the humpback population around Australia. The odds of a whale of this population deviating from the trajectory along the eastward course are greater than that of a whale deviating when traveling in the reverse direction.
Schall, on the other hand, suspects that the clockwise flow of water around Antarctica, known as the Antarctic Circumpolar Current, is at least partially responsible. A male humpback that becomes separated from its population in the middle of a migration may simply drift east with the current until it encounters other humpbacks.
“I imagine it could be that, but evidently it’s difficult to prove that it is,” Schall said.
To fully understand the remarkable spread of humpback songs, researchers will have to understand why humpbacks sing in the first place. Many scientists suspect that humpback calls are like birdsong: they are intended to make females feel attracted to males.
This is just a hypothesis for now. Ornithologists have already demonstrated that a male bird’s song is crucial to its reproductive success. But it is far more difficult to track the reproductive habits of a male humpback on the high seas.
Sprucing up a corner can be a way for the male to stand out. “There’s an impulse to look for something that’s new,” commented Garland. “Whether females like it, that’s the big question.”
