A humpback whale breaching in waters off French Polynesia. Whales in Australia were found to be passing their songs to others in French Polynesia, which in turn gave songs to whales in Ecuador.
(Photo: Ellen Garland)
Humpback whale songs from the central to the eastern South Pacific
(Audio via Royal Society Open Science)
Humpback Whales Pass Their Songs Across Oceans
Whales share songs from Australia to Ecuador, scientists have found, suggesting a remarkably fast cultural evolution.
by Carl Zimmer
https://www.nytimes.com/2022/08/30/science/humpback-whale-songs-cultural-evolution.html
One of the most remarkable things about our species is how fast human culture can change. New words can spread from continent to continent, while technologies such as cellphones and drones change the way people live around the world.
It turns out that humpback whales have their own long-range, high-speed cultural evolution, and they don’t need the internet or satellites to keep it running.
In a study published on Tuesday, scientists found that humpback songs easily spread from one population to another across the Pacific Ocean. It can take just a couple of years for a song to move several thousand miles.
Ellen Garland, a marine biologist at the University of St. Andrews in Scotland and an author of the study, said she was shocked to find whales in Australia passing their songs to others in French Polynesia, which in turn gave songs to whales in Ecuador.
“Half the globe is now vocally connected for whales,” she said. “And that’s insane.”
It’s even possible that the songs travel around the entire Southern Hemisphere. Preliminary studies by other scientists are revealing whales in the Atlantic Ocean picking up songs from whales in the eastern Pacific.
Each population of humpback whales spends the winter in the same breeding grounds. The males there sing loud underwater songs that can last up to half an hour. Males in the same breeding ground sing a nearly identical tune. And from one year to the next, the population’s song gradually evolves into a new melody.
Dr. Garland and other researchers have uncovered a complex, language-like structure in these songs. The whales combine short sounds, which scientists call units, into phrases. They then combine the phrases into themes. And each song is made of several themes.
Male humpbacks sometimes change a unit in their song. Sometimes they add a new phrase or chop out a theme. The other males may then copy it. These embellishments cause the population’s song to gradually evolve, resulting in drastically different melodies from one population to the next.
Michael Noad, a marine biologist at the University of Queensland, discovered that a population’s song can sometimes make a sudden, dramatic change. In 1996, he and his colleagues noticed that a male on the east coast of Australia had given up the local song and was now singing a tune that matched one previously sung on the west coast of the country.
Within two years, all of the males on the east coast were singing that song. Dr. Noad’s landmark study was the first to discover this kind of cultural revolution in any animal species.
Dr. Garland earned her doctoral degree with Dr. Noad in the early 2000s, recording humpback songs in breeding grounds farther east in the Pacific Ocean. When she compared their songs, she found the same pattern as Dr. Noad had: Songs sung in eastern Australia showed up within a couple years in French Polynesia about six thousand miles away.
After publishing that initial discovery in 2011, Dr. Garland continued to record humpback whales on the same breeding grounds. She also wondered if their songs were spreading farther east across the Pacific.
An opportunity to find out arrived when Judith Denkinger and Javier Oña, marine biologists at the University of San Francisco de Quito in Ecuador, offered to collaborate. They study humpback whales that breed on the coast of Ecuador.
For their new study, Ms. Denkinger and Mr. Oña recorded humpback whales from 2016 to 2018. Over the same period, Michael Poole, a marine biologist at the Marine Mammal Research Program on the French Polynesian island of Moorea, recorded whales there.
The researchers set up anchored underwater microphones that could eavesdrop on whales passing through. They also followed whales by boat, sticking microphones into the water to catch their songs.
In 2016 and 2017, the two populations of whales had clearly distinct songs. But in 2018, a revolution happened: The whales in Ecuador were putting French Polynesian themes in their songs.
The scientists reported their findings on Tuesday in the journal Royal Society Open Science.
Elena Schall, a postdoctoral researcher at the Alfred Wegener Institute in Bremerhaven, Germany, who was not involved in the study, said that she is seeing some similar patterns in the Atlantic Ocean. Humpback whales off the coast of Brazil and South Africa are picking up themes previously recorded off the coast of Ecuador.
It is conceivable, Dr. Schall said, that songs flow all the way around the Southern Hemisphere. “It’s possible, but there’s a data gap in the Indian Ocean,” she said. “I think that will definitely be the next step, if we can find enough data to compare.”
Dr. Garland and Dr. Schall agreed that the songs are most likely spreading as humpbacks leave their breeding grounds and migrate to foraging grounds close to Antarctica. On that journey, a male humpback may end up swimming alongside males from another population. When they hear his radically different song, they may borrow some themes or steal the entire song. They will keep singing their new song when they return to their breeding grounds.
As for why songs mainly flow from west to east, Dr. Garland said it might be because of the huge size of the humpback population around Australia. The chances that a whale from that population to veer off course to the east are greater than one straying the other way.
Dr. Schall, on the other hand, suspects the clockwise flow of water around Antarctica — known as the Antarctic Circumpolar Current — is at least partly responsible. A male humpback that gets separated from his migrating population may just drift east with the current until he encounters other whales.
“I could imagine it’s maybe this, but of course it’s hard to prove,” Dr. Schall said.
Regina Guazzo, a marine biologist at the U.S. Navy’s Whale Acoustic Reconnaissance Project who was not involved in the study, said that the discoveries about humpbacks make her wonder if other whale species are also sharing songs across entire oceans.
“Although humpback whales have been studied the most extensively, other species of whales also sing complex songs that we are just beginning to understand,” Dr. Guazzo said.
To fully understand the remarkable spread of humpback whale songs, researchers will need to figure out why they sing in the first place. Many researchers suspect that humpback songs are like bird songs, serving to attract females to males.
For now, that’s just a hypothesis. Ornithologists have demonstrated that a male bird’s song is crucial to his reproductive success. But it’s a lot harder to track the mating habits of a male humpback on the high seas.
Embellishing a song may be a way for him to stand out. “There’s this drive to novelty,” Dr. Garland said. “Whether females like it is the big question.”
That same impulse could account for the revolutions Dr. Garland and her colleagues are documenting in humpback songs. If a migrating male happens to encounter a male from another population, he may borrow the new song to make himself even more attractive than a minor embellishment could.
“These big changes jump out of the water at us, to our ears,” Dr. Garland said. “So I would assume they would be noticeable to females.”