Whales communicate across an enormous span of the sound spectrum, from rumbling infrasound below 20 Hz all the way up to ultrasonic clicks above 100 kHz. The specific frequency depends almost entirely on whether you are talking about baleen whales or toothed whales, two groups that diverged tens of millions of years ago and evolved radically different vocal systems. Baleen whales like blues and fins produce some of the lowest-pitched sounds of any animal on Earth, while toothed whales like dolphins and porpoises operate at frequencies so high they are inaudible to the human ear. The full story involves anatomy, ocean physics, predator evasion, and a puzzling trend that scientists still cannot fully explain.
Baleen Whales and Low-Frequency Sound
Baleen whales, the group that includes blue, fin, humpback, and right whales, are the bass section of the ocean. They produce calls at low frequencies of 200 Hz and below, and some species dip into true infrasound, meaning frequencies under 20 Hz that fall below the threshold of human hearing entirely.1Fossil Record. Relationships of cochlear coiling shape and hearing frequencies in cetaceans, and the occurrence of infrasonic hearing in Miocene Mysticeti To put that in perspective, the lowest note on a standard piano is about 27.5 Hz. Blue whales routinely call below that.
Blue whale calls are often described as pulsed tones centered near 20 Hz, which is right at the boundary between what humans can and cannot hear. Fin whales produce characteristic 20 Hz pulses as well, short low-frequency bursts repeated in regular patterns that researchers use to track their seasonal movements across entire ocean basins.2Frontiers in Remote Sensing. Widespread passive acoustic monitoring reveals spatio-temporal patterns of blue and fin whale song vocalizations in the Northeast Pacific Ocean These sounds can travel hundreds or even thousands of kilometers through the deep ocean, because low-frequency sound waves lose energy much more slowly than high-frequency ones as they propagate through water. For an animal that may need to find a mate across vast stretches of open ocean, broadcasting at the lowest possible frequency makes practical sense.
Humpback whales are a notable exception among baleen whales because their songs span a broader frequency range. While the core of humpback song sits in the hundreds-of-hertz range, researchers recording humpback song units off Hawaii found that some sounds contained harmonics extending beyond 24 kHz, which was the upper recording limit of their equipment.3The Journal of the Acoustical Society of America. Acoustic properties of humpback whale song Those are the highest harmonic levels ever documented in humpback song. Whether the whales themselves or other whales can perceive those high harmonics is still debated, but it shows that the acoustic output of even a “low-frequency” baleen whale is more complex than a simple bass rumble.
Toothed Whales and High-Frequency Sound
Toothed whales occupy the opposite end of the frequency spectrum. This group includes dolphins, porpoises, beaked whales, and sperm whales, and their sounds range from a few kilohertz up past 130 kHz. Much of what toothed whales produce serves double duty: the same click trains used for echolocation also carry social information, and many species layer in whistles and burst-pulse calls that are purely communicative.
Bottlenose dolphins, probably the best-studied toothed whale, produce signature whistles that function like individual names. In wild populations off Namibia, researchers measured signature whistles with mean minimum frequencies between roughly 2.6 and 8.3 kHz and mean maximum frequencies between about 9.9 and 20 kHz. The highest individual whistle recorded reached 22.58 kHz, just above the upper limit of human hearing. The average peak frequency across all measured whistle types was around 8.2 kHz.4PLOS ONE. Identification and Characteristics of Signature Whistles in Wild Bottlenose Dolphins (Tursiops truncatus) from Namibia So if you could somehow hear a dolphin’s signature whistle in air, it would sound like a high-pitched, rapidly modulated tone, a bit like a sliding whistle instrument played at the top of its range.
Sperm whales take a different approach. Instead of whistles, they communicate using patterns of clicks arranged into sequences called codas. Recent analysis of sperm whale codas has identified distinct spectral patterns within these click sequences, with pronounced frequency concentrations below 10 kHz. Researchers found at least two separate spectral shapes in sperm whale codas: one with a single strong frequency peak near 5,780 Hz and another with two peaks near 3,757 Hz and 6,579 Hz. The researchers drew an analogy to human vowel sounds, where different vowels are distinguished by where their frequency peaks sit.5MIT Press PMC. Vowel- and Diphthong-Like Spectral Patterns in Sperm Whale Codas The finding suggests that sperm whale communication may carry more layered information than the simple rhythmic patterns that researchers had focused on for decades.
How Whales Actually Make Sound
Whales do not have vocal cords in the way that land mammals do. Toothed whales generate their clicks and whistles using a set of specialized structures in their nasal passages, not in the throat. Dissections across every major toothed whale family have revealed a consistent anatomy: a pair of small fatty structures called phonic lips (or “monkey lips”) embedded in connective tissue, along with a cartilaginous support, a stout ligament, and a system of air sacs that recycle air internally so the whale does not need to exhale while producing sound.6Journal of Morphology. Functional morphology and homology in the odontocete nasal complex: Implications for sound generation The consistency of this anatomy across dolphins, porpoises, beaked whales, and sperm whales suggests that all toothed whales produce their biosonar signals through the same basic mechanism, even though the resulting frequencies vary enormously depending on the size and tuning of those structures.
Baleen whales produce sound differently. They have a larynx with specialized folds, though the exact mechanism is still less well understood than in toothed whales. The working model involves air passing over tissue folds in the larynx, similar in concept (though not in scale) to how human vocal cords work. The sheer size of a baleen whale’s vocal apparatus helps explain the extremely low frequencies: larger vibrating structures naturally produce lower pitches, the same reason a bass guitar string is thicker and longer than a treble string.
Why Water Changes Everything About Sound
Sound moves roughly five times faster through seawater than through air, which has counterintuitive effects on how whale calls behave. Because of this speed difference, the wavelengths of sounds traveling through water are compressed compared to what they would be in air. One consequence is that higher-frequency sounds travel farther through water than they would through an equivalent distance in air, losing less energy along the way.7PubMed Central. Does size matter? Examining the drivers of mammalian vocalizations This helps explain why dolphins and porpoises can use clicks in the tens or even hundreds of kilohertz range for echolocation and still get useful echoes back from objects at a distance. In air, sounds at those frequencies would be absorbed within meters.
For baleen whales, the physics works even more in their favor. Low-frequency sound in the deep ocean can travel extraordinary distances, especially when it enters the deep sound channel, a layer of water at several hundred meters depth where the speed of sound hits a minimum. Sound waves entering this channel get refracted back toward it from above and below, effectively trapping the energy and allowing it to propagate with remarkably little loss. Blue whale calls near 20 Hz traveling through this channel can theoretically be detected across an entire ocean basin. Whether individual whales are actually listening at those ranges is harder to know, but the physical potential is there.
Stealth Communication and Acoustic Crypsis
Not every whale wants to be heard across an ocean. In situations where being loud is dangerous, some whales deliberately go quiet, a behavior researchers call acoustic crypsis. The most striking examples come from mother-calf pairs in species vulnerable to killer whale predation.
Southern right whale mothers with calves vocalize at very low rates, fewer than 10 calls per hour, and at notably low volumes. Researchers tagging lactating southern right whales in Australian breeding grounds measured received call levels between about 123 and 134 decibels, far quieter than the calls of other right whale demographic groups. The interpretation is that these mothers are minimizing their acoustic footprint to avoid attracting killer whales, which could threaten their calves.8PubMed. Acoustic crypsis in southern right whale mother-calf pairs: infrequent, low-output calls to avoid predation?
North Atlantic right whale mothers use a similar but slightly different strategy. Rather than just turning down the volume on their normal calls, these mothers switch their entire vocal repertoire when calves are present. They produce a higher proportion of very quiet call types that are rarely detected in recordings from other demographic groups of right whales, such as pregnant females or juveniles.9PubMed Central. Acoustic crypsis in communication by North Atlantic right whale mother–calf pairs on the calving grounds So it is not just a volume knob being turned down: the mothers are using a separate, quieter communication mode that appears to have evolved specifically for the high-risk period when calves are small and vulnerable.
The Porpoise Frequency Arms Race
Some toothed whales have taken stealth in a completely different direction: instead of going quiet, they went ultrasonic. Harbor porpoises and Dall’s porpoises produce echolocation clicks that are narrowband and extremely high frequency, with essentially no energy below 100 kHz.10PLoS ONE. Clicking in a Killer Whale Habitat: Narrow-Band, High-Frequency Biosonar Clicks of Harbour Porpoise (Phocoena phocoena) and Dall’s Porpoise (Phocoenoides dalli) That 100 kHz threshold is significant because it happens to be the upper effective hearing limit of killer whales, their main predator. Porpoises can hear killer whale calls just fine, but killer whales cannot hear porpoise clicks. Researchers have described this as an “acoustic arms race”: the porpoises have evolved a communication and echolocation system that operates entirely above the predator’s hearing range, making them effectively invisible to killer whale sonar.
This comes with trade-offs. Very high-frequency sounds attenuate faster in water, meaning porpoise clicks do not carry nearly as far as the lower-frequency clicks of, say, a bottlenose dolphin. A porpoise’s effective echolocation range is therefore shorter. But the survival advantage of being undetectable to killer whales apparently outweighs the cost of a shorter detection range. Several unrelated groups of small toothed whales, including porpoises, some river dolphins, and certain pygmy sperm whales, have independently converged on similar narrowband high-frequency click designs, which suggests the evolutionary pressure has been strong enough to drive the same solution multiple times.
Why Blue Whale Calls Keep Getting Deeper
One of the more puzzling findings in whale acoustics is that blue whale call frequencies have been declining for decades. Since blue whale calls were first recorded in the 1960s, the pitch of their vocalizations has been slowly dropping, and the trend shows no sign of leveling off.11PubMed Central. Update on frequency decline of Northeast Pacific blue whale (Balaenoptera musculus) calls This is not a subtle fluctuation. The decline is measurable over both annual and multi-year timescales and has been documented in blue whale populations worldwide.
The trend is not limited to blue whales. Researchers analyzing seven years of continuous acoustic recordings in the southern Indian Ocean found that fin whales, Antarctic blue whales, and pygmy blue whales all showed a steady frequency decrease at a rate of a few tenths of a hertz per year since 2002.12Journal of Geophysical Research: Oceans. Long‐Term and Seasonal Changes of Large Whale Call Frequency in the Southern Indian Ocean A few tenths of a hertz per year may sound tiny, but over decades it adds up. Blue whale B-calls that were once centered near 20 Hz have shifted noticeably lower.
Nobody has a satisfying explanation. Hypotheses range widely. One suggestion is that as baleen whale populations recover from commercial whaling, individual whales do not need to call as loudly or at as high a frequency to reach potential mates, because there are simply more whales to hear them. A lower-frequency call produced at the same energy level would travel farther with less effort. Another hypothesis involves increasing ocean noise from shipping, which is concentrated at low frequencies and could create selective pressure for whales to shift their calls to avoid masking. But the trend predates the era of heavy shipping traffic in some regions, and some populations are declining in frequency even faster than ocean noise is increasing. The honest answer is that this remains an open question, one that touches on whale physiology, population dynamics, and ocean acoustics in ways that researchers are still trying to untangle.
How Shipping Noise Affects Whale Communication
Ocean noise from commercial shipping, seismic surveys, and sonar exercises is concentrated in the same low-frequency bands that baleen whales rely on. The overlap is a growing concern for whale communication. But whales do not all respond to noise the same way.
North Atlantic right whales adjust their call volume in response to background noise, much the way a person raises their voice in a noisy bar. Individual right whales increase the amplitude of their calls during periods of heightened noise, a behavior called the Lombard effect that has also been documented in birds and primates.13Europe PMC. Individual right whales call louder in increased environmental noise This helps maintain the range over which their calls can be detected by other whales, but it costs energy and may not fully compensate for the masking effect of chronic noise.
Humpback whales in at least one population take a different approach. Rather than calling louder or shifting their frequency, humpbacks near the Ogasawara Islands in Japan appeared to stop singing temporarily when shipping noise was present.14PLoS ONE. Change in singing behavior of humpback whales caused by shipping noise They did not modify the acoustic characteristics of their song; they simply paused it. That raises a different kind of concern. If a humpback stops singing during a critical period for mate attraction, the communication is not just degraded, it is eliminated entirely until the noise passes. In busy shipping lanes, the windows of silence for singing may keep shrinking.
Frequency as Identity
For many whale species, the frequency and structure of calls are not just about reaching the right distance. They carry identity information. Bottlenose dolphin signature whistles are frequency-modulated patterns that are individually distinctive and stable over years. When dolphins encounter each other, they exchange signature whistles in a way that appears to function like exchanging names. The frequency contour of the whistle, the way it sweeps up and down across the kilohertz range, is what makes each whistle unique rather than the absolute pitch at which it is produced.
Sperm whale codas carry group identity information as well. Different sperm whale clans use different coda repertoires, patterns of clicks that are consistent within a social unit but distinct between units. The recently discovered vowel-like spectral patterns within individual codas add another potential layer of information encoding.5MIT Press PMC. Vowel- and Diphthong-Like Spectral Patterns in Sperm Whale Codas If sperm whales are indeed modulating the spectral envelope of their clicks to produce something analogous to vowel distinctions, the combinatorial possibilities for encoding information in click sequences expand considerably. This is an active and rapidly evolving area of research, and the tools for analyzing whale vocalizations are becoming more powerful every year as machine-learning methods get applied to large passive acoustic datasets.
Among baleen whales, population-level identity is often embedded in frequency and song structure. Blue whale populations in different ocean basins produce calls at slightly different frequencies and with different temporal patterns, enough that researchers can reliably identify which population a recorded call belongs to based on its acoustic signature alone. These regional “dialects” appear to be culturally transmitted, though the mechanism for that transmission is not well understood. What is clear is that frequency is not just a byproduct of body size or physics for whales. It is a medium for carrying biologically meaningful information, from individual names to group membership to reproductive status, across distances that no land animal could match.