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That controversial paper was born of the Cold War. To listen for Soviet submarines, the U.S. Navy installed chains of underwater listening posts in the Pacific and Atlantic. This network, known as the Sound Surveillance System, or SOSUS, picked up a deluge of oceanic noises. Some were clearly biological. Others were more mysterious. One especially enigmatic sound was monotonous, repetitive, and low, with a frequency of 20 Hz—an octave below the lowest key on a standard piano. This hum was so loud that people doubted it could be coming from an animal. Did it have a military origin? Was it produced by underwater tectonic activity? Did it come from waves crashing on some distant shoreline? The actual source only became clear when Navy scientists started following the sounds to their sources, and often found a fin whale at the end.

Human hearing typically bottoms out at around 20 Hz. Below those frequencies, sounds are known as infrasound, and they’re mostly inaudible to us unless they’re very loud. Infrasounds can travel over incredibly long distances, especially in water. Knowing that fin whales also produce infrasound, Payne calculated, to his shock, that their calls could conceivably travel for 13,000 miles. No ocean is that wide. Together with oceanographer Douglas Webb, Payne published his calculations, speculating that the largest whales “may be in tenuous acoustic contact throughout a relatively enormous volume of ocean.” The response was brutal. Leading whale researchers told him that his paper was pure fantasy. Colleagues hinted that critics had been questioning his mental health behind his back. “When you get to distances like that, people just refuse to believe that it’s true,” Payne tells me.

Payne’s work made a more positive impression on Chris Clark. A young acoustician and former choirboy, Clark was recruited by Roger and Katy Payne to be a sound technician on a 1972 trip to Argentina to study right whales. It was a thrilling and formative time. Camped on a beach beneath the Southern Cross, with penguins bumbling past and albatrosses wheeling overhead, Clark began listening to whales. He placed hydrophones in the water to eavesdrop on their songs and found ways of assigning specific recordings to individual whales. He went on to compile libraries of whale calls, recorded all over the world, from Argentina to the Arctic. And all the while, Payne’s idea of giant whales talking over oceans stuck with him.

In the 1990s, with the Cold War over and the threat of Soviet subs diminished, the Navy offered Clark and others a chance to observe real-time recordings from their SOSUS hydrophones. Amid the spectrograms—visual representations of the sounds that SOSUS picked up—Clark saw the unmistakable signal of a singing blue whale. On his first day, Clark saw that more blue whale vocalizations had been recorded from a single SOSUS sensor than had been described before in the entire scientific literature. The ocean was awash with their calls, and those calls were coming in from enormous distances. Clark calculated that one individual was 1,500 miles from the sensor that recorded it. He could listen to whales singing in Ireland with a microphone situated off Bermuda. “I just thought: Roger was right,” he says. “It is physically possible to detect a blue whale singing across an ocean basin.” (...)

Although blue and fin whale songs can traverse oceans, no one knows if the whales actually communicate at such ranges. It’s possible that they’re signaling to nearby individuals with very loud calls, which just happen to extend further afield. But Clark points out that they repeat the same notes, over and over again, and at very precise intervals. A singing whale will stop calling when it surfaces for air, and come back on the beat when it submerges. “That’s not arbitrary,” he says. It reminds him of the redundant and repetitive signals that Martian rovers use to beam data back to Earth. If you wanted to design a signal that could be used to communicate across oceans, you’d come up with something similar to a blue whale’s song.

Those songs might have other uses, too. Their notes can last for several seconds, with wavelengths as long as a football field. Clark once asked a Navy friend what he could do with such a call. “I could illuminate the ocean,” the friend replied. That is, he could map distant underwater landscapes, from submerged mountains to the seafloor itself, by processing the echoes returning from the far-reaching infrasounds. Geophysicists can certainly use fin whale songs to map the density of the ocean crust. But can the whales do so?

Clark sees evidence in their movements. Through SOSUS, he has seen blue whales emerging in polar waters between Iceland and Greenland and making a beeline—a whaleline?—for tropical Bermuda, singing all the way. He has seen whales slaloming between underwater mountain ranges, zigging and zagging between landmarks hundreds of miles apart. “When you watch these animals move, it’s as if they have an acoustic map of the oceans,” he says. He also suspects that the animals can build up such maps over their long lives, accruing sound-based memories that lurk in their mind’s ear. After all, Clark recalls veteran sonar specialists telling him that different parts of the sea had their own distinctive sounds. “They said: If you put a pair of headphones on me, I can tell you if I’m near Labrador or off the Bay of Biscay,” says Clark. “I thought that if a human being could do this in 30 years, what could an animal do with 10 million years?”

The scale of a whale’s hearing is hard to grapple with. There’s the spatial vastness, of course, but also an expanse of time. Underwater, sound waves take just under a minute to cover 50 miles. If a whale hears the song of another whale from a distance of 1,500 miles, it’s really listening back in time by about half an hour, like an astronomer gazing upon the ancient light of a distant star. If a whale is trying to sense a mountain 500 miles away, it has to somehow connect its own call with an echo that arrives 10 minutes later. That might seem preposterous, but consider that a blue whale’s heart beats around 30 times a minute at the surface, and can slow to just 2 beats a minute on a dive. They surely operate on very different timescales than we do. If a zebra finch hears beauty in the milliseconds within a single note, perhaps a blue whale does the same over seconds and minutes. To imagine their lives, “you have to stretch your thinking to completely different levels of dimension,” Clark tells me. He compares the experience to looking at the night sky through a toy telescope and then witnessing its full majesty through NASA’s spaceborne Hubble telescope. When he thinks about whales, the world feels bigger, stretching out in space and time.

Whales weren’t always big. They evolved from small, hoofed, deer-like animals that took to the water around 50 million years ago. Those ancestral creatures probably had vanilla mammalian hearing. But as they adapted for an aquatic life, one group of them—the filter-feeding mysticetes, which include blues, fins, and humpbacks—shifted their hearing to low infrasonic frequencies. At the same time, their bodies ballooned into some of the largest Earth has ever seen. These changes are probably connected. The mysticetes achieved their huge size by evolving a unique style of feeding, which allows them to subsist upon tiny crustaceans called krill. Accelerating into a krill swarm, a blue whale expands its mouth to engulf a volume of water as large as its own body, swallowing half a million calories in one gulp. But this strategy comes at a cost. Krill aren’t evenly distributed across the oceans, so to sustain their large bodies, blue whales must migrate over long distances. The same giant proportions that force them to undergo these long journeys also equip them with the means to do so—the ability to make and hear sounds that are lower, louder, and more far-reaching than those of other animals.

Back in 1971, Roger Payne speculated that foraging whales could use these sounds to stay in touch over long distances. If they simply called when fed and stayed silent when hungry, they could collectively comb an ocean basin for food and home in on bountiful areas that lucky individuals have found. A whale pod, Payne suggested, might be a massively dispersed network of acoustically connected individuals, which seem to be swimming alone but are actually together."

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