Deep in the world’s oceans, male sperm whales may be broadcasting one of the most powerful and unusual communication signals produced by any mammal. Their slow clicks can exceed 200 decibels referenced to 1 micropascal, travel through the deep ocean for an estimated 70 kilometres, and arrive at intervals so precise that researchers compare the rhythm to a metronome operating on an extraordinarily slow setting.
The clicks are not the rapid echolocation signals sperm whales use to locate squid in darkness. Nor are they the short, patterned sequences known as codas, which play an important role in the species’ social communication. Instead, these signals are low-frequency clicks produced at repetition rates of approximately 0.1 to 0.3 hertz, meaning that the interval between clicks can last from roughly three to ten seconds. Despite the long pauses, male whales maintain the timing with remarkable consistency.
An international research team analysed slow clicks recorded in waters around the Seychelles, Sri Lanka, Norway and Scotland. Their findings, published in Annals of the New York Academy of Sciences, suggest that these sounds represent a distinct form of long-range communication. The study examined both the physical properties of the clicks and the environmental conditions that determine how far they can travel. The researchers found that the combination of extreme source level, low frequency, long range and precise rhythm is what makes the signals especially unusual.
The biological purpose of the clicks remains uncertain. Because the signals appear to be produced primarily by males, one possibility is that they function as an acoustic advertisement. A large male sperm whale has a much larger sound-producing organ than a smaller male, and the size of that organ can influence the frequency and power of the sound. In this scenario, a deep, intense click could provide information about the caller’s body size, potentially attracting females or discouraging rival males. The sound might effectively announce the presence of a powerful animal across a vast area of ocean.
Sperm whales possess the largest known sound-producing organ of any animal. This enormous nasal complex can weigh more than five tonnes in a fully grown male and may account for about one-third of the whale’s body length. Inside it are structures known as phonic lips, which work somewhat like a biological valve. When the whale forces air through the nasal system, the phonic lips are driven together, generating acoustic pulses. The whale’s surrounding tissues and air sacs then help shape and amplify the resulting sound.
The most powerful measurements came from a male sperm whale recorded off the Seychelles. Researchers lowered a hydrophone, an underwater microphone, approximately four metres below the surface from the research vessel R/V Odyssey. The whale was within about 200 metres of the instrument, and the team used distance measurements to estimate the sound level at a standard range of one metre. From a 30-minute recording containing 65 slow clicks, the strongest signal reached 226 decibels referenced to 1 micropascal at one metre.
That figure cannot be directly compared with decibel levels measured in air. Underwater acoustics uses a reference pressure of 1 micropascal, while airborne sound is normally referenced to 20 micropascals. Water also transmits sound differently from air because it is denser and has different acoustic properties. Nevertheless, within the scale used by marine scientists, a source level above 200 decibels is extraordinarily powerful—comparable in some respects to intense artificial sources such as powerful sonar systems and seismic surveying equipment.
The estimated 70-kilometre active space is also highly dependent on ocean conditions. Temperature and salinity determine how sound bends through the water, while depth and the shape of the seabed influence reflections and transmission paths. Background noise is another major factor. Commercial shipping, construction and other human activities can mask biological sounds, reducing the distance over which whales can detect one another. A signal capable of travelling dozens of kilometres in a quiet deep-ocean environment may become detectable over only a few kilometres in a noisy area.
The rhythm of the slow clicks raises another intriguing question: how do the whales keep time when each beat may be separated by several seconds? The researchers speculate that sperm whales could use echoes from the seafloor or other environmental features as an acoustic timing reference. A powerful click sent downward might return after a predictable delay, depending on the depth of the seabed and the speed of sound in the water. The whale could potentially use that returning echo as an environmental stopwatch, although there is currently no evidence proving that this is how the rhythm is maintained.
The next step will be to determine how other sperm whales respond. Researchers hope to use playback experiments involving underwater loudspeakers and sound-recording tags attached to whales with suction cups. They could test whether males answer the clicks, approach or avoid the source, and whether females react differently. Changes in frequency, intensity or repetition rate may reveal what information the signals carry. For now, the evidence supports the existence of a powerful and highly rhythmic communication system—but not a whale “language.” The slow clicks may be advertisements, territorial warnings or signals with an entirely different function, offering scientists a new way to study how sound connects animals across the immense spaces of the deep sea.
Subject of Research:
Male sperm whale slow-click communication and its acoustic properties.
Article Title:
Extreme Rhythm Keeping in Long-Range Slow Click Communication of Sperm Whales
News Publication Date:
18-Jun-2026
Web References:
https://doi.org/10.1111/nyas.70289
References:
Annals of the New York Academy of Sciences, “Extreme Rhythm Keeping in Long-Range Slow Click Communication of Sperm Whales.” DOI: 10.1111/nyas.70289
Image Credits:
Simone Videsen, Aarhus University
Keywords:
Sperm whales, whale communication, slow clicks, underwater acoustics, marine biology, bioacoustics, echolocation, whale behavior, ocean noise, animal communication
