Sperm whale clicks: the most powerful communication signal in the animal kingdom

How can two large predators separated by tens of kilometres of deep ocean signal to one another? An international team led by Aarhus University provides a measured answer for the sperm whale: the slow clicks of males are the most powerful communication signal ever measured in an animal, with a range estimated at 70 kilometres. But the study’s most remarkable result lies elsewhere, in a value that comes close to arithmetical perfection: 0.501.

Four types of click, not to be confused

Despite its large brain and elaborate social life, the sperm whale has a limited vocal repertoire: four types of click, produced by the largest sound-producing organ in the animal kingdom. This nasal complex accounts for a third of the body length in a mature male and weighs more than five tonnes.

Click type	Function	Frequency	Rate	Source level
Usual clicks	long-range echolocation	10 to 20 kHz	1 to 3 Hz	up to 240 dB
Buzzes	final pursuit of prey	high	≈ 50 Hz	low
Codas	close-range social communication	3 to 4 kHz	sequences of 3 to 11 clicks in 1 s	≈ 170 dB
Slow clicks	long-range communication, males only	≈ 4 kHz	0.1 to 0.3 Hz	196 dB median

Slow clicks are produced exclusively by males, which show marked sexual dimorphism, both in overall size and in the relative proportions of the blowhole. Five to ten seconds separate two consecutive clicks. The study deals with this fourth category, the least documented.

Credit: Simone Videsen, AU

Method

For the power. Off the Seychelles, a calibrated hydrophone was lowered to four metres from the vessel R/V Odyssey, while an observer measured the distance to the animal with a laser rangefinder; it never exceeded 200 metres. The identification of the emitter is rigorous: the inter-pulse interval of 7.2 milliseconds corresponds to an animal of fifteen metres, a size that only males reach. Sixty-five usable clicks were extracted from a thirty-minute recording.

For the rhythm. The analysis draws on a much larger corpus: 1,839 slow clicks from six sites, in the Seychelles, Sri Lanka, Norway and at three points in Scotland, that is 56 independent recordings and 1,783 intervals. The data were collected with towed hydrophones, moored autonomous recorders and DTAG tags attached to males by suction cup.

For the range. It is not measured but modelled, by acoustic ray tracing, assuming a source placed either near the surface or at 620 metres, in the heart of the SOFAR channel where sound travels particularly far.

Power and range: exactly what the figures say

The median level measured is 196 dB peak to peak at one metre, with an interquartile range of 193 to 203, and a few clicks reaching 226 dB. This upper value is probably the closest to the level actually emitted on the beam axis, since the orientation of the animal relative to the hydrophone is not known for every click.

These levels are best placed by comparison, in the same unit. Slow clicks exceed the whistles and burst pulses of dolphins by about 40 decibels, and the low-frequency calls of blue whales and fin whales by 10 to 20 decibels. The sperm whale’s own codas are some thirty decibels below them.

One crucial nuance, missing from the press coverage: the most powerful sound is not the one that carries furthest. The calls of blue whales and fin whales last about a hundred times longer than a sperm whale click and therefore carry more energy. Emitted at around 15 to 20 hertz, frequencies that seawater barely absorbs, they can under good conditions be detected at a thousand kilometres, well beyond the sperm whale’s 70 kilometres. The record established here concerns the source level, not the distance travelled.

The 70 kilometres remain remarkable among odontocetes nonetheless: one to two orders of magnitude more than in any other toothed whale. An asymmetry follows, which the study underlines. A female can hear a distant male, but cannot answer him beyond three to ten kilometres, the range of her own signals. Only males can hold an exchange at this scale, over an area exceeding 10,000 square kilometres.

The central result: isochrony at 0.501

To analyse the rhythm, the authors compute for each pair of successive intervals a rhythm ratio: the duration of the first interval divided by the sum of the two. If the two intervals are exactly equal, this ratio is exactly 0.5. That is the definition of isochrony, the steady beat of a metronome.

Across the 1,783 intervals analysed, the peak of the distribution falls at 0.501, as does the median, with a mean of 0.502. The median interval between two clicks is 5.15 seconds, with three preferred rates at 3.2, 4.7 and 7.7 seconds. The authors also note secondary peaks at the 1:2 and 2:1 ratios, that is intervals exactly double or half the preceding one, and statistically significant.

In other words, these animals hold a five-second beat with metronome precision, and can also shift cleanly to double or half the tempo. This rate is an order of magnitude slower than any other rhythmic signal known in mammals and birds, where 1 hertz or more is typical.

How do they keep the beat?

The difficulty deserves to be taken seriously, because intuition handles it badly. In humans, the regular production of a voluntary movement degrades markedly as soon as the interval exceeds three quarters of a second, and the accuracy of temporal judgement falls away beyond one second, with a ceiling somewhere around three seconds. We manage it only by mentally subdividing the interval, by counting. Nothing indicates that a non-human animal proceeds in this way.

The usual explanations do not work either. A mechanical resonance of the sound-producing apparatus is not very plausible, since the rate varies within a single individual and between individuals. External biological rhythms, circadian or ultradian, are three to six orders of magnitude too slow. Nor does the sperm whale show the relative hypertrophy of the cerebellum seen in small odontocetes, to which their temporal precision is attributed.

Two hypotheses remain, which the authors explicitly present as speculative.

An internal clock: the heart. The heart rate of a diving sperm whale has never been measured, but extrapolation from smaller marine mammals places it around 0.1 hertz, precisely the range of slow clicks. A fine perception of its own heartbeat could serve as a reference.

An external clock: the echo from the seafloor. A click emitted downwards returns as an echo after a delay set by the depth. A male that holds its depth above an even seafloor thus receives a very stable temporal cue on which to set the next click. The authors judge this the more likely of the two, and recall an old and puzzling observation: a sperm whale appeared to align its intervals with those of a ship’s echo sounder.

This second hypothesis has an elegant consequence. A receiver that knows the local depth from its own echolocation could, by analysing the multiple echoes that follow each click, estimate the distance of the emitting male. The signal would then carry its own scale.

The function remains unknown

The function remains unknown. The authors are explicit: only a playback experiment, emitting recorded clicks towards tagged animals, could demonstrate it. An honest advertisement of size or maturity, a dominance signal meant to avoid the physical fights attested by the scars and broken jaws of old males, or some other use: the question stands.

The information content is low. The authors describe the signal as low entropy. At long range, the internal detail of the click is lost to distortion and multipath propagation; all that survives is the sex of the emitter, inferred from the click type, and the interval between two clicks. It is precisely this poverty that makes the message robust. This is in no sense a language, and our page on the brain and cognition of cetaceans sets out why the distinction matters.

The 70 kilometres are a ceiling. The modelling assumes an ambient noise of 40 decibels per hertz. Close to dense shipping traffic, the effective range collapses. A signal shaped to cross an ocean basin is then brought back to the animal’s immediate surroundings, a mechanism documented on our page on anthropogenic ocean noise.

To place these sounds in relation to one another, our sound library and our page on the acoustic profile of cetaceans give examples, and the one on the melon of odontocetes explains the anatomy that produces them.

Reference: Videsen S. K. A., Raimondi T., Sørensen P. M., Pedersen M. B., Zimmer W. M. X., van Geel N. C. F., Risch D., Cook P., King S. L., Ravignani A. and Madsen P. T., “Extreme Rhythm Keeping in Long-Range Slow Click Communication of Sperm Whales”, Annals of the New York Academy of Sciences, 1559(1), e70289, 18 May 2026. Open-access article, with published peer review. Aarhus University press release distributed by EurekAlert. Funding: Human Frontier Science Program and European Research Council. The authors dedicate their article to Roger Payne, who died in 2023 and who made the song of the humpback whale known to the world.