Whales employ diverse acoustic signals for both communication and sensory perception. The specific sound production mechanisms differ across various cetacean families. Marine mammals, encompassing whales, dolphins, and porpoises, exhibit a significantly higher reliance on sound compared to terrestrial mammals, primarily due to the diminished efficacy of other senses in aquatic environments. Visual perception is less effective for marine mammals because oceanic particulates scatter light. Olfactory capabilities are also restricted, as molecular diffusion occurs more slowly in water than in air, thereby reducing the effectiveness of smell. Conversely, the velocity of sound in water is approximately three times greater than in the atmosphere at sea level. Given the profound dependence of marine mammals on audition for communication and foraging, environmental scientists and cetologists express apprehension regarding potential harm from escalating ambient noise levels in global oceans, attributed to shipping, sonar, and marine seismic surveys.
Whales use a variety of sounds for communication and sensation. The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, including whales, dolphins, and porpoises, are much more dependent on sound than land mammals due to the limited effectiveness of other senses in water. Sight is less effective for marine mammals because of the way particulates in the ocean scatter light. Smell is also limited, as molecules diffuse more slowly in water than in air, which makes smelling less effective. However, the speed of sound is roughly three times greater in water than in the atmosphere at sea level. As sea mammals are so dependent on hearing to communicate and feed, environmentalists and cetologists are concerned that they are being harmed by the increased ambient noise in the world's oceans caused by ships, sonar and marine seismic surveys.
The term "song" characterizes the consistent and foreseeable acoustic sequences produced by certain whale species, particularly the humpback whale. These vocalizations are often likened to human music, with male humpback whales notably described as "inveterate composers" of melodies that bear a "'striking similarity' to human musical traditions." Nevertheless, subsequent research has introduced complexities to this perspective. While it has been proposed that humpback songs convey male fitness to female whales, this hypothesis has encountered challenges based on multiple arguments.
Categories and Functions of Vocalization
Although the intricate vocalizations of humpback whales (and certain blue whales) are primarily associated with sexual selection, other whale species generate simpler sounds that serve alternative, year-round functions. Observers have documented mother whales gently guiding their calves towards the surface in a playful manner, simultaneously emitting a sound akin to human cooing. This cooing-like vocalization appears to soothe their young and represents one of several distinct daily sounds produced by whales. In contrast to some fish, such as sharks, odontocetes (toothed whales) lack an olfactory sense, compelling them to depend extensively on echolocation for both prey acquisition and navigation in dark oceanic conditions. Consequently, these whales must produce sounds continuously throughout the year to effectively circumvent potential obstructions, including submerged vessels or other organisms.
Furthermore, whales have been demonstrated to be highly social organisms. The vocalizations produced consistently throughout the year—primarily whistles, clicks, and pulsed calls—facilitate communication among members of their pod. Each distinct sound emitted by a whale may convey a unique meaning. Specifically, the clicking sounds produced by whales are utilized for navigational purposes.
The inquiry into whether whales vocalize solely for aesthetic pleasure, individual gratification, or "for art's sake" is regarded by some as an "untestable question."
Humpback Whale Vocalizations
Scholarly interest in whale vocalizations was stimulated by researchers Katy and Roger Payne, alongside Scott McVay. Their attention was drawn to these sounds by Frank Watlington, a Bermudian employed by the U.S. government at the SOFAR station, where he monitored for Russian submarines using underwater hydrophones off the island's coast. In 1970, the Paynes released the highly successful album Songs of the Humpback Whale. Subsequently, these whale vocalizations were rapidly integrated into human musical compositions by various artists, including singer Judy Collins, George Crumb, Paul Winter, and David Rothenberg.
The humpback whale generates a sequence of repetitive vocalizations across diverse frequencies, collectively termed whale song. Marine biologist Philip Clapham characterizes these vocalizations as "probably the most complex in the animal kingdom."
Male humpback whales frequently engage in these vocalizations during the mating season, leading to the initial hypothesis that their purpose was to facilitate mate selection. Nevertheless, subsequent research has yielded no evidence establishing a direct link between these vocalizations and reproductive success.
The songs exhibit a hierarchical organization. The fundamental units of the song, informally referred to as "notes," are discrete, continuous sound emissions persisting for several seconds. These sounds exhibit a frequency range from 20 Hz to over 24 kHz, whereas the standard human auditory range spans 20 Hz to 20 kHz. These units can be frequency-modulated, meaning their pitch may ascend, descend, or remain constant, or they can be amplitude-modulated, indicating variations in loudness. Nevertheless, analyzing the song's spectrogram with adjusted bandwidth settings uncovers the inherent pulsed characteristic of frequency-modulated sounds.
A sub-phrase comprises four to six units and typically endures for approximately ten seconds. Two sub-phrases combine to form a phrase. Individual whales commonly reiterate a single phrase for durations of two to four minutes, establishing what is termed a theme. Multiple themes collectively constitute a song. A complete whale song can extend for up to 30 minutes and is frequently repeated over periods spanning hours or even days. This nested, 'Russian doll' organizational structure implies a syntactic complexity more akin to human language than to other animal communication forms, such as bird songs, which typically exhibit only linear arrangements.
Within a specific geographical region, all whales produce nearly identical songs at any given moment, yet these songs undergo continuous and gradual evolution over time. For instance, a unit initially characterized by an upsweep (an increase in frequency) may progressively flatten into a constant note over a month. Similarly, another unit might exhibit a consistent increase in amplitude. The rate of a whale song's evolution is also variable; in certain years, songs may transform rapidly, while in others, minimal changes are observed.
Whales inhabiting shared geographical territories, potentially spanning entire ocean basins, typically produce comparable songs, exhibiting only minor variations. Conversely, whales from distinct, non-overlapping regions vocalize entirely dissimilar songs.
During the evolutionary process of the song, previously established patterns do not appear to be re-adopted. A comprehensive analysis of whale songs spanning 19 years revealed that although overarching patterns were discernible, identical combinations of elements were never repeated.
Humpback whales also produce discrete vocalizations independent of their structured songs, particularly during courtship displays. Additionally, humpbacks emit a third category of sound, designated as the feeding call. This vocalization is prolonged, lasting between 5 and 10 seconds, and maintains a nearly constant frequency. Humpbacks typically engage in cooperative feeding, forming groups to swim beneath fish shoals before collectively lunging vertically through the fish and breaching the water surface. These feeding calls precede the coordinated lunges. The precise function of this call remains undetermined.
Certain researchers have posited that humpback whale songs might fulfill an echolocative function; however, this hypothesis has encountered scholarly debate.
Additional Whale Vocalizations
Beyond their songs, humpback whales are observed to produce various other social vocalizations for communication, including "grunts," "groans," "thwops," "snorts," and "barks."
Research conducted in 2009 revealed a progressive deepening in the tonal frequency of blue whale songs since the 1960s. Despite a more than 12-decibel increase in ambient ocean noise due to pollution since the mid-20th century, researcher Mark McDonald noted that an upward shift in pitch would be anticipated if whales were exerting effort to be audible.
Killer whales are known to emit both stereotyped, high-frequency long-range calls, capable of traversing distances of 10–16 km (6.2–9.9 mi), and short-range calls, which propagate 5–9 km (3.1–5.6 mi). Short-range vocalizations are typically documented during social interactions and resting phases, whereas long-range calls are more frequently associated with foraging and feeding activities.
The majority of other cetaceans, including whales and dolphins, generate vocalizations exhibiting diverse levels of complexity. Notably, beluga whales, often referred to as "sea canaries," emit an extensive repertoire of whistles, clicks, and pulses. A captive male beluga named NOC (pronounced 'no-see') was observed spontaneously mimicking the vocal patterns of adult male human speech, which are considerably lower in pitch than typical beluga vocalizations. To achieve these frequencies, he intentionally overinflated his vestibular sac, an anatomical feature belugas normally employ to prevent water entry into the blowhole, thereby regulating pressure within his nasal tract.
Initially, it was hypothesized that most baleen whales vocalize within a frequency range of approximately 15–20 hertz. However, a research team led by Mary Ann Daher from the Woods Hole Oceanographic Institution documented in New Scientist in December 2004 the long-term tracking of a whale in the North Pacific over a 12-year period, which produced vocalizations at an anomalous 52 Hz. The scientific community has yet to provide a definitive explanation for this unique phenomenon. While 52 Hz constitutes a very low frequency for human hearing, perceptible as a faint moaning sound, the typical vocalizations of other whales are generally below the threshold of human audibility. This particular whale was not presumed to represent a novel species; rather, its vocalizations suggested that an existing species might possess a significantly broader vocal range than previously understood. Nevertheless, scholarly debate persists regarding the distinctiveness of this whale's vocalization and the possibility of its classification as a hybrid, akin to documented blue and fin whale hybrids.
Mechanisms of Sound Production
Humans generate voiced sounds through the controlled passage of air across the larynx. Within the larynx, the adduction of the vocal cords causes the airflow to induce their rapid, alternating closure and opening. This action segments the continuous airstream into discrete air pulses, which are perceived as a vibration. Subsequent modification of this vibration by articulatory organs within the oral and nasal cavities results in the complex sounds characteristic of human speech.
Cetacean sound production diverges significantly from the human physiological mechanism. The specific processes involved vary between the two cetacean suborders: the Odontoceti, encompassing toothed whales and dolphins, and the Mysticeti, which includes baleen whales and the largest marine mammals, such as the blue whale.
Odontocete Whales
Odontocetes generate rapid sequences of high-frequency clicks, primarily utilized for echolocation. Specialized anatomical structures within these whales produce a range of clicks and buzzes, spanning frequencies from 0.2 to 150 kHz, enabling them to acquire acoustic data about their surroundings. Lower frequencies are employed for long-range echolocation, as longer wavelengths propagate more effectively underwater than shorter ones. Conversely, higher frequencies prove more efficacious over shorter distances, providing more granular details about a target. The echoes derived from these clicks transmit comprehensive information, including the target's distance, size, morphology, velocity, and directional movement. Furthermore, echolocation facilitates the odontocete's capacity to differentiate objects based on their material composition and density, even when visually indistinguishable. Remarkably, individual odontocetes appear capable of isolating their own echoes during communal feeding activities, thereby avoiding interference from the echolocations of other pod members.
In contrast to clicks, whistles serve a communicative function among odontocetes. Calves, typically between four and six months of age, develop distinctive vocalizations, termed "signature whistles," which they employ consistently throughout their lifespan. These signature whistles are unique to each individual and are hypothesized to facilitate identification within odontocete social groups. Despite the diverse array of vocalizations produced by large dolphin pods, the precise semantic content of these sounds remains largely unelucidated. Frankel cites a researcher who metaphorically describes the acoustic environment of an odontocete school as analogous to the cacophony of a children's playground.
Odontocetes generate their diverse vocalizations by directing air through a cephalic structure known as the phonic lips. Biologically, this structure is homologous to an upper lip situated within the nasal cavity; however, its mechanistic function closely resembles that of human vocal folds, which are located in the larynx. As air traverses this constricted passage, the membranes of the phonic lips are drawn together, inducing vibrations in the adjacent tissues. These vibrations, much like those in the human larynx, are subject to highly sensitive conscious control. The resulting vibrations propagate through the cranial tissues to the melon, an organ that sculpts and directs the sound into a focused beam, essential for echolocation. With the exception of the sperm whale, all toothed whales possess two distinct sets of phonic lips, enabling them to produce two independent sounds concurrently. Following passage through the phonic lips, the air enters the vestibular sac, from which it can either be recirculated into the inferior portion of the nasal complex for subsequent sound generation or expelled via the blowhole.
The French term for phonic lips, museau de singe, directly translates to "monkey's muzzle," a descriptor derived from the perceived resemblance of this anatomical structure in sperm whales. Advanced cranial analyses conducted in 2004, utilizing computed axial and single-photon emission computed tomography scans, revealed that in bottlenose dolphins, air can be supplied to the nasal complex directly from the lungs. This mechanism allows for the sustained production of sound as long as the dolphin can replenish air from its respiratory system.
Sperm Whale
Sperm whale vocalizations are exclusively click-based, categorized into four distinct types: standard echolocation, creaks, codas, and slow clicks. Codas represent the most characteristic vocalizations, consisting of brief, rhythmic click sequences, typically comprising 3 to 12 clicks arranged in standardized patterns. These vocalizations emerge from vocal learning processes within stable social units. Certain codas convey clan identity, indicating variations in travel, foraging, and social interaction or avoidance behaviors among different clans. Functioning as "arbitrary traits that serve as dependable indicators of cultural group affiliation," clan identity codas operate as symbolic cues that regulate inter-individual interactions.
The expression of individual identity through sperm whale vocalizations remains a subject of ongoing scientific investigation. It is crucial to differentiate between acoustic cues and deliberate signals. While human acoustic analysis tools can differentiate individual whales by examining subtle characteristics of their vocalizations, and whales likely possess a similar capacity, this does not confirm that whales intentionally employ specific vocalizations to signal individual identity, unlike the signature whistles used by bottlenose dolphins for individual recognition.
Mysticete Whales
Mysticetes lack a phonic lip structure; instead, their larynx appears instrumental in sound production. This is evidenced by the presence of vocal fold homologs within a U-shaped fold supported by arytenoid cartilages. These whales can produce sound without exhaling, as they retain air within a laryngeal sac. It is hypothesized that air from this sac is recycled back to the lungs for subsequent vocalizations. Although mysticetes do not possess bony cranial sinuses, they do have a pterygoid air sac. The precise function of this sac in sound production is uncertain (potentially resonance), but its primary role is likely auditory, as it seems to maintain an airspace around the ear ossicles at depth.
Vocal Plasticity and Acoustic Behavior
Globally, at least nine distinct acoustic populations of blue whales have been identified. Over the past five decades, blue whales have exhibited a shift in their vocalizations, with calls progressively decreasing in frequency. For instance, Australian pygmy blue whales are reducing their mean call frequency at an approximate rate of 0.35 Hz per year.
The migratory behaviors of blue whales are not fully understood. Certain populations occasionally appear to reside in highly productive habitats year-round, whereas others engage in extensive migrations to high-latitude feeding areas. However, the full scope of these migrations and the specific population segments involved remain largely uncharacterized.
Sound Levels
Baleen whale vocalizations span a frequency range from 10 Hz to 31 kHz. Representative sound levels are presented in the subsequent table.
Human Interaction
Researchers employ hydrophones, frequently adapted from their initial military application in submarine tracking, to precisely determine the origin of whale vocalizations. These methodologies also enable the assessment of sound propagation distances within oceanic environments. Studies conducted by Dr. Christopher Clark of Cornell University, utilizing military data, demonstrated that whale sounds can traverse thousands of kilometers. Beyond insights into song production, this data facilitates the tracking of whale migratory routes during the "singing" (mating) season. A significant discovery is that whales exhibit the Lombard effect, modifying their vocalizations to counteract ambient noise pollution.
Furthermore, evidence indicates that blue whales cease producing foraging D calls upon the activation of mid-frequency sonar, despite the sonar's frequency range (1–8 kHz) significantly exceeding their own sound production range (25–100 Hz).
Studies reveal a decadal doubling of ambient noise from marine vessels, which consequently diminishes the audible range of whale vocalizations. Historically, before the advent of extensive shipping, whale sounds potentially traversed entire ocean basins. Environmental advocates express concern that this escalating boat activity imposes significant stress on marine fauna and impedes their reproductive success.
Over the last decade, numerous efficacious automated methodologies, including signal processing, data mining, and machine learning techniques, have been developed for the detection and classification of whale vocalizations.
History
Whaling Captain Wm. H. Kelly is credited as the first individual to identify whale vocalizations as distinct "singing" during his voyage on the brig Eliza in the Sea of Japan in 1881.
Upon his appointment as an Associate in Physical Oceanography at the Woods Hole Oceanographic Institution (WHOI) in Massachusetts in 1943, William E. Schevill's initial research focused on the echolocation of U-boats under the patronage of the U.S. Navy. In 1962, he articulated: "During World War II many people on both sides listened to underwater sounds for military reasons. Not only the wanted sounds (those made by enemy ships), but a bewildering variety of others were heard. Most of these were ascribed to animals living in the sea, usually as 'fish noises' ... Some were ascribed to whales, in part correctly, but without identification of the kind of whale; most military listeners were not biologists, and in any case the traditional naval sonar room is woefully deficient in windows." Schevill pioneered the recording of underwater whale sounds and subsequently deduced their functional significance from these acoustic data. His seminal contributions resulted in more than fifty publications on whale phonation, thereby establishing the foundational framework for "literally hundreds of scientific studies produced by other workers from the 1960s until the present day." Notably, his wife, Barbara Lawrence, who served as Curator of Mammals at the Harvard Museum of Comparative Zoology (MCZ), frequently co-authored these scholarly works.
William E. Schevill's research into whales eventually intersected with the U.S. Naval operations that initially inspired his career trajectory. Following his passing, the Society for the Bibliography of Natural History observed: "Bill helped defuse a tense moment between the USA and Soviet Union during the Cold War. The US military suspected that low frequency blips were being used by the Soviets to locate American submarines, whereas Bill showed these were produced by fin whales (Balaenoptera physalus) hunting prey."
Media
Selected Discography
- The album Songs of the Humpback Whale (SWR 118) was initially issued in 1970 by CRM Records, featuring recordings by Roger Payne, Frank Watlington, and other contributors. This LP was subsequently re-released by Capitol Records, distributed as a flexible disc within the National Geographic Society magazine, Volume 155, Number 1, in January 1979. Further re-releases include a CD version by Living Music/Windham Hill/BMG Records in 1992, and a remastered CD by BGO-Beat Goes On in 2001.
- Deep Voices: The Second Whale Record (Capitol/EMI Records 0777 7 11598 1 0) was launched as an LP in 1977, comprising supplementary recordings by Roger Payne. It was later re-issued on CD in 1995 by Living Music/Windham Hill/BMG Records, featuring vocalizations from humpback, blue, and right whales.
- Northern Whales (MGE 19) was published by Music Gallery Editions, utilizing recordings by Pierre Ouellet, John Ford, and other researchers associated with Interspecies Music and Communication Research. This compilation features vocalizations from belugas, narwhals, orcas, and bearded seals.
- The CD Sounds of the Earth: Humpback Whales (Oreade Music) was released in 1999.
- Rapture of the Deep: Humpback Whale Singing (Compass Recordings) became available on CD in 2001.
- The album Songlines: Songs of the East Australian Humpback whales. was released in 2009.
52-hertz whale
- 52-hertz whale
- Bioacoustics
- Biomusic
- Underwater acoustics
- Vocal learning