Deep in the world’s oceans, the large male sperm whales emit slow, low frequency clicks with the highest source levels of any animal communication sounds.
These slow clicks are not echolocation clicks the whales otherwise use to locate prey, but instead loud, low frequency communication signals.
This is the conclusion of an international research team that has measured and analysed sperm whale slow clicks in the waters off the Seychelles, Sri Lanka, Norway and Scotland.
Their research suggests that male sperm whales use a kind of reverse clickbait. It is not bait designed to make someone click. The click itself may be the bait.
Whether the clicks are in fact the whales’ version of “look at me!” to females, “keep away!” to other males – or something else entirely – the researchers do not yet know. But they have plans to find out.
Sperm whales are famous for their clicks. They use clicks to find squid in the dark at great depths by echolocation, and also use short rhythmic click packages, known as codas, in their social communication.
But these slow clicks are different.
As far as the researchers know, they are produced exclusively by males. They are slower, lower frequency and more powerful than the social coda clicks. There can be five to ten seconds between each click. Even so, the whales keep the rhythm with a precision comparable to a drummer playing very, very slowly.
This surprised the researchers.
“What is extreme about slow clicks is that the whales can produce them with long time intervals between them. And they can do it very rhythmically. And over those distances. It is really the combination of the three things that is extreme: the strength, the rhythm and the range,” says Simone Videsen, a postdoc at Aarhus University.
She is first author of the study, which has just been published in the respected scientific journal Annals of the New York Academy of Sciences.
The reason the sperm whale can make such powerful clicks lies in its highly unusual anatomy.
The male has the world’s largest sound-producing organ: a gigantic nasal complex, which in a fully grown animal can weigh more than five tonnes and makes up about one third of the body length.
This is where the so-called phonic lips are found. These are car tire sized structures in the nose that the whale snaps together to create clicks.
“A big nose sits on a big male, and a big nose will produce a lower-frequency click. That makes slow clicks interesting, because the clicks may tell us something about the male producing them. The sound may therefore function as an honest signal of size – what we biologists call honest advertisement,” explains Professor Peter Teglberg Madsen, a senior-author of the study, also from Aarhus University.
In other words: if a male sperm whale clicks at a low pitch and high volume, it may tell both females and rivals that here comes a large male worth paying attention to.
But that is still a hypothesis.
The researchers still do not know why male sperm whales produce the slow clicks. They know that the clicks exist. They now know how powerful they can be, how far they can potentially travel, and how precisely the whales keep the rhythm.
But they do not know how other whales respond to them. And that is an important point, they emphasie.
“Could it be linked to honest advertisement, sexual selection, territorial enforcement or something else entirely? We hope to carry out a new study that can find explanations through playback experiments,” says Simone Videsen.
In such experiments, the researchers hope to attach small recording computers to whales and play slow clicks from underwater loudspeakers to see whether the whales react – and how.
Does a male respond by starting to click himself? Does he come closer? Does he swim away? Do females react differently from males? And does it matter whether the clicks are slightly deeper, faster or slower?
Although the clicks are communication, they should not be called a language, Peter Teglberg Madsen stresses.
Sperm whales are social animals with large brains, and their communication is the subject of intense research.
“But I warn against making them more human than the data can support. We have to distinguish between language and communication. This is, by all indications, click communication, but it is not a language,” he says.
The new study is therefore not about translating sperm whale conversations. It is about something more fundamental: understanding how a mammal can use sound to send a rhythmic signal through enormous volumes of water.
The researchers measured how powerful slow clicks are close to the whales emitting them, and then used sound models to calculate how far they can be heard under typical deep-water conditions. The result is a possible range of up to 70 kilometres.
However, the distance is affected by the conditions in the ocean – temperature, salinity, depth, seabed and background noise.
And human-made noise may matter.
If there are ships nearby, the natural soundscape of the ocean can become so noisy that the whales’ communication range becomes markedly shorter. Instead of dozens of kilometres, in some situations the signal may perhaps only travel a few kilometres before it cannot be detected.
One of the most puzzling questions is how the whales keep the slow rhythm so precisely.
Humans can keep a rhythm. We can clap in time, snap our fingers or play drums. But if there are five to ten seconds between each beat, it becomes difficult to keep the rhythm without counting in your head.
The researchers do not think that sperm whales count to ten. Instead, they have another idea.
Perhaps the whales use their surroundings as a stopwatch. When a male sends a powerful click down through the water, the sound may hit the seabed and return as an echo. If the echo comes back after five, six, seven or eight seconds, the whale may perhaps use it as a signal to send the next click.
“We do not know whether they do this, but it would be a way for them to use the environment as a stopwatch,” says Peter Teglberg Madsen.
If that is correct, the whale is not only using the ocean as a place to send sound through. It is using the ocean space itself – the distance to the seabed and the travel time of sound – as a way to keep the beat.
The researchers measured sound source levels from male sperm whales of more than 200 dB re 1 µPa. Sound pressure in water is measured using a different reference from the one used to measure sound pressure in air. So, the 200 dB should not be compared with the noise from jet aircraft or rock concerts.
But on the scale used in underwater acoustics, 200 dB re 1 µPa is extremely powerful – in the same range as powerful sonars and sound sources used for seismic surveys of the seabed.
And these are produced by an animal. With its nose.
How do you measure the sound of a sperm whale?
You go to sea, find a whale, lower a hydrophone – an underwater microphone – into the water and at the same time measure the distance to the whale with a laser.
That is how the researchers measured the sound level of slow clicks from a male sperm whale off the Seychelles. The hydrophone hung four metres below the surface from the research vessel R/V Odyssey, while the whale was no more than 200 metres away.
When you know both the sound picked up by the hydrophone and the distance to the whale, you can calculate back to how powerful the click must have been when it left the whale’s five-tonne nose.
The researchers analysed 65 slow clicks from a 30-minute recording. The most powerful reached 226 dB re 1 µPa at a distance of one metre.
The rhythm itself was studied using recordings from several places around the world – including the Seychelles, Sri Lanka, Norway and Scotland. Here, the researchers used hydrophones from boats, acoustic recorders in the water and DTAGs – small instruments attached to whales with suction cups.
And the range of up to 70 kilometres is calculated using models of how sound moves through the deep ocean.
Annals of the New York Academy of Sciences
Extreme Rhythm Keeping in Long-Range Slow Click Communication of Sperm Whales
18-Jun-2026
The authors declare no conflicts of interest.