Whale sounds

Whale sounds are the sounds made by whales and which are used for different kinds of communication.[1]

The word "song" is used to describe the pattern of regular and predictable sounds made by some species of whales, notably the Humpback Whale. This is included with or in comparison with music, and male humpback whales have been described as "inveterate composers" of songs that are "'strikingly similar' to human musical traditions".[2] Male Humpback whales sing only on calving grounds and only in the mating period and humpback songs are similar, almost identical, within a single population. It has been suggested that humpback songs communicate male fitness to female whales.[3] The click sounds made by Sperm whales and dolphins are not strictly song, but the clicking sequences have been suggested to be individualized rhythmic sequences that communicate the identity of a single whale to other whales in its group and allows the groups to coordinate foraging activities.[4]

The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, such as whales, dolphins, and porpoises, are much more dependent on sound for communication and sensation than are land mammals, because other senses are of limited effectiveness in water. Sight is less effective for marine mammals because of the way water absorbs light. Smell also is limited, as molecules diffuse more slowly in water than in air, which makes smelling less effective. However, the speed of sound is roughly four times greater in water than in the atmosphere at sea level. Because 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.

Contents

Production of sound

Humans produce sound by expelling air through the larynx. The vocal cords within the larynx open and close as necessary to separate the stream of air into discrete pockets of air. These pockets are shaped by the throat, tongue, and lips into the desired sound, allowing humans to speak.

Cetacean sound production differs markedly from this mechanism. The precise mechanism differs in the two major suborders of cetaceans: the Odontoceti (toothed whales—including dolphins) and the Mysticeti (baleen whales—including the largest whales, such as the Blue Whale).

Odontocete whale sound production

Toothed whales do not make the long, low-frequency sounds known as the whale song. Instead, they produce rapid bursts of high-frequency clicks and whistles. Single clicks are generally used for echolocation whereas collections of clicks and whistles are used for communication. Though a large pod of dolphins will produce a wide range of different noises, very little is known about the meaning of the sound. Frankel quotes one researcher who says listening to a school of odontocetes is like listening to a group of children at a school playground.[5]

The multiple sounds odontocetes make are produced by passing air through a structure in the head called the phonic lips. This structure functions like the human nasal cavity. As the air passes through this narrow passage, the phonic lip membranes are sucked together, causing the surrounding tissue to vibrate. These vibrations can, as with the vibrations in the human larynx, be consciously controlled with great sensitivity. The vibrations pass through the tissue of the head to the melon, which shapes and directs the sound into a beam of sound useful in echolocation. Every toothed whale except the sperm whale has two sets of phonic lips and is thus capable of making two sounds independently.[6] Once the air has passed the phonic lips it enters the vestibular sac. From there, the air may be recycled back into the lower part of the nasal complex, ready to be used for sound creation again, or passed out through the blowhole.

The French name for phonic lips, museau de singe, translates literally as "monkey's muzzle," which the phonic lip structure is supposed to resemble.[7] New cranial analysis using computed axial and single photon emission computed tomography scans in 2004 showed, at least in the case of bottlenose dolphins, that air might be supplied to the nasal complex from the lungs by the palatopharyngeal sphincter, enabling the sound creation process to continue for as long as the dolphin is able to hold its breath.[8]

Mysticete whale sound production

Baleen whales (formally called mysticetes) do not have phonic lip structure. Instead, they have a larynx that appears to play a role in sound production, but it lacks vocal cords and scientists remain uncertain as to the exact mechanism. The process, however, cannot be completely analogous to humans, because whales do not have to exhale in order to produce sound. It is likely that they recycle air around the body for this purpose. Cranial sinuses may also be used to create the sounds, but again researchers are currently unclear how.

Mysticete whale sound levels

The frequency of baleen whale sounds ranges from 10 Hz to 31 kHz.[9] A list of typical levels is shown in the table below.

Source Broadband source level (dB re 1 \muPa at 1m) [10]
Fin whale moans 155–186
Blue whale moans 155–188
Gray whale moans 142–185
Bowhead whale tonals, moans and song 128–189

Purpose of whale-created sounds

While the complex sounds of the Humpback whale (and some blue whales) are believed to be primarily used in sexual selection, the simpler sounds of other whales have a year-round use. While toothed whales are capable of using echolocation to detect the size and nature of objects, this capability has never been demonstrated in baleen whales. Further, unlike some fish such as sharks, a whale's sense of smell is not highly developed. Thus, given the poor visibility of aquatic environments and that sound travels so well in water, sounds audible to humans may play a role in navigation. For instance, the depth of water or the existence of a large obstruction ahead may be detected by loud noises made by baleen whales.

The singing of whale songs for aesthetic enjoyment, personal satisfaction, or 'for art's sake', is "an untestable question in scientific terms."[11]

Song of the Humpback Whale

 Two groups of whales, the Humpback Whale and the subspecies of Blue Whale found in the Indian Ocean, are known to produce a series of repetitious sounds at varying frequencies. This is known as whale song. Marine biologist Philip Clapham describes the song as "probably the most complex in the animal kingdom".[12]

Male humpback whales perform these vocalizations only during the mating season, and so it is believed the purpose of songs is to aid sexual selection.[5] Whether the songs are a competitive behavior between males seeking the same mate, a means of defining territory or a "flirting" behavior from a male to a female is not known and the subject of ongoing research. Males have been observed singing while simultaneously acting as an "escort" whale in the immediate vicinity of a female. Singing has also been recorded in competitive groups of whales that are composed of one female and multiple males.

Interest in whale song was aroused by researchers Roger Payne and Scott McVay after the songs were brought to their attention by a Bermudian named Frank Watlington who was working for the US government at the SOFAR station listening for Russian submarines with underwater hydrophones off the coast of the island.[13]

The songs follow a distinct hierarchical structure. The base units of the song (sometimes loosely called the "notes") are single uninterrupted emissions of sound that last up to a few seconds. These sounds vary in frequency from 20 Hz to 10 kHz (the typical human range of hearing is 20 Hz to 20 kHz). The units may be frequency modulated (i. e., the pitch of the sound may go up, down, or stay the same during the note) or amplitude modulated (get louder or quieter). However the adjustment of bandwidth on a spectrogram representation of the song reveals the essentially pulsed nature of the FM sounds.

A collection of four or six units is known as a sub-phrase, lasting perhaps ten seconds (see also phrase (music)). A collection of two sub-phrases is a phrase. A whale will typically repeat the same phrase over and over for two to four minutes. This is known as a theme. A collection of themes is known as a song. The whale will repeat the same song, which last up to 30 or so minutes, over and over again over the course of hours or even days. This "Russian doll" hierarchy of sounds has captured the imagination of scientists.

All the whales in an area sing virtually the same song at any point in time and the song is constantly and slowly evolving over time. For example, over the course of a month a particular unit that started as an "upsweep" (increasing in frequency) might slowly flatten to become a constant note.[5] Another unit may get steadily louder. The pace of evolution of a whale's song also changes—some years the song may change quite rapidly, whereas in other years little variation may be recorded.[5]

Whales occupying the same geographical areas (which can be as large as entire ocean basins) tend to sing similar songs, with only slight variations. Whales from non-overlapping regions sing entirely different songs.[5]

As the song evolves, it appears that old patterns are not revisited.[5] An analysis of 19 years of whale songs found that while general patterns in song could be spotted, the same combination never recurred.

Humpback whales may also make stand-alone sounds that do not form part of a song, particularly during courtship rituals.[14] Finally, humpbacks make a third class of sound called the feeding call. This is a long sound (5 to 10 s duration) of near constant frequency. Humpbacks generally feed cooperatively by gathering in groups, swimming underneath shoals of fish and all lunging up vertically through the fish and out of the water together. Prior to these lunges, whales make their feeding call. The exact purpose of the call is not known, but research suggests that fish know what it means. When the sound was played back to them, a group of herring responded to the sound by moving away from the call, even though no whale was present.

Some scientists have proposed that Humpback Whale songs may serve an echolocative purpose,[15] but this has been subject to disagreement.[16]

Other whale sounds

Humpback whales have also been found to make a range of other social sounds to communicate such as "grunts", "groans", "thwops", "snorts" and "barks".[17]

Most baleen whales make sounds at about 15–20 hertz. However, marine biologists, led by Mary Ann Daher, at the Woods Hole Oceanographic Institution reported in New Scientist in December 2004 that she had been tracking a whale in the North Pacific for 12 years that was "singing" at 52 Hz.[18] The scientists are unable to explain this dramatic difference from the norm; however, they believe the whale is baleen[19] and unlikely to be a new species,[18] suggesting that currently known species may have a wider vocal range than previously thought.

In 2009, researchers found that blue whale song has been deepening in its tonal frequency since the 1960s.[20] While noise pollution has increased ambient ocean noise by over 12 decibels since the mid-20th century, researcher Mark McDonald indicated that higher pitches would be expected if the whales were straining to be heard.[21]

Most other whales and dolphins produce sounds of varying degrees of complexity. Of particular interest is the Beluga (the "sea canary") which produces an immense variety of whistles, clicks and pulses.

Human interaction

Though some observers suggest that undue fascination has been placed on the whales' songs simply because the animals are under the sea, most marine mammal scientists believe that sound plays a particularly vital role in the development and well-being of cetaceans.

Researchers use hydrophones (often adapted from their original military use in tracking submarines) to ascertain the exact location of the origin of whale noises. Their methods allow them also to detect how far through an ocean a sound travels. Research by Dr. Christopher Clark of Cornell University conducted using military data showed that whale noises travel for thousands of kilometres.[22] As well as providing information about song production, the data allows researchers to follow the migratory path of whales throughout the "singing" (mating) season. One important finding is that whales in a process called the Lombard effect adjust their song to compensate for background noise pollution.[23]

Prior to the introduction of human noise production, Clark says the noises may have travelled right from one side of an ocean to the other, agreeing with a thirty-year-old concept blaming large-scale shipping.[22] His research indicates that ambient noise from boats is doubling with each decade.[22] This has the effect of reducing the range at which whale noises can be heard. Environmentalists fear that such boat activity is putting undue stress on the animals as well as making it difficult to find a mate.[22]

Media

See also: List of whale songs

Selected discography

See also

References

  1. ^ Communication and behavior of whales, R Payne. 1983. Westview Press
  2. ^ Payne Roger, quoted in: Author(s): Susan Milius. "Music without Borders", p. 253. Source: Science News, Vol. 157, No. 16, (15 April 2000), pp. 252-254. Published by: Society for Science & the Public.
  3. ^ A.J. Wright and A Walsh (2010) Mind the gap: why neurological plasticity may explain seasonal interruption in humpback whale song. Journal of the Marine Biological Association of the United Kingdom, 90(8), 1489–1491.
  4. ^ Michel Andre and Cees Kamminga (2000) Rhythmic dimension in the echolocation click trains of sperm whales: a possible function of identification and communication Journal of Marine Biological Association of the United Kingdom, Vol. 80, pp. 163-169.
  5. ^ a b c d e f Frankel, Adam S. "Sound production", Encyclopedia of Marine Mammals, 1998, pp. 1126–1137. ISBN 0-12-551340-2
  6. ^ Fitch; W.T. Neubauer; and Herzel J. (2002). "Calls out of chaos: the adaptive significance of nonlinear phenomena in mammalian vocal production". Anim. Behav. 63: 407–418. 
  7. ^ Ted W. Cranford. "Selcted Wahle Sciences Images - Volume 1". http://www.spermwhale.org/SpermWhale/spermwhaleorgV1.html. Retrieved 2010-10-20. 
  8. ^ Houser, Dorian S.; Finneran, James; Carder, Don; Van Bonn, William; Smith, Cynthia; Hoh, Carl; Mattrey, Robert; and Ridgway, Sam (2004). "Structural and functional imaging of bottlenose dolphin (Tursiops truncatus) cranial anatomy". Journal of Experimental Biology 207 (Pt 21): 3657–3665. doi:10.1242/jeb.01207. PMID 15371474. 
  9. ^ Richardson, Greene, Malme, Thomson (1995). Marine Mammals and Noise. Academic Press. ISBN 978-0125884402. 
  10. ^ Kuperman, Roux (2007). "Underwater Acoustics". In Rossing, Thomas D.. Springer Handbook of Acoustics. Springer. ISBN 978-0387304465. 
  11. ^ Entomologist Thomas Eisner, quoted in: Milius (2000), p.254 though the production of sound out of ecstasy, is common among the toothed species.
  12. ^ Clapham, Philip (1996). Humpback whales. Colin Baxter Photography. ISBN 0-948661-87-9. 
  13. ^ Rothenberg, David (2008). Thousand mile song. Basic Books. ISBN 978-0465071289. 
  14. ^ Mattila, David. K; Guinee, Linda N., Mayo, Charles A. (1987). "Humpback Whale Songs on a North Atlantic Feeding Ground". Journal of Mammalogy (American Society of Mammalogists) 68 (4): 880–883. doi:10.2307/1381574. JSTOR 1381574. 
  15. ^ Mercado, E. III, and Frazer, L.N. (2001). "Humpback whale song or humpback whale sonar? A Reply to Au et al." (PDF). IEEE Journal of Oceanic Engineering 26: 406–415. doi:10.1109/48.946514. http://www.acsu.buffalo.edu/~emiii/00946514.pdf. 
  16. ^ W. W. L. Au, A. Frankel, D. A. Helweg, and D. H. Cato (2001). "Against the humpback whale sonar hypothesis". IEEE Journal of Oceanic Engineering 26: 295–300. doi:10.1109/48.922795. 
  17. ^ Cecilia Burke, ''A whale's varied vocabulary', Australian Geographic, AG Online, accessed online August 7, 2010
  18. ^ a b "Lonely whale's song remains a mystery". New Scientist (Reed Business Information Ltd). 11 December 2004. http://www.newscientist.com/article/mg18424774.600-lonely-whales-song-remains-a-mystery.html. Retrieved 12 July 2009. 
  19. ^ Associated Press (13 December 2004). "Strange-voiced whale at large in the ocean". Daily Times. http://www.dailytimes.com.pk/default.asp?page=story_13-12-2004_pg6_14. Retrieved 12 July 2009. 
  20. ^ McDonald, Mark A., Hildebrand, John A., Mesnick, Sarah. Worldwide decline in tonal frequencies of blue whale songs. Endangered Species Research, Vol. 9 No. 1 23 October 2009.
  21. ^ Keim, Brandon. Blue Whale Song Mystery Baffles Scientists. Wired (magazine). 2 December 2009.
  22. ^ a b c d Bentley, Molly (28 February 2005). "Unweaving the song of whales". BBC News. http://news.bbc.co.uk/1/hi/sci/tech/4297531.stm. Retrieved 12 July 2009. 
  23. ^ Scheifele PM, Andrew S, Cooper RA, Darre M, Musiek FE, Max L. (2005). St. Lawrence River beluga Indication of a Lombard vocal response in the St. Lawrence River Beluga. J Acoust Soc Am. 117(3 Pt 1):1486–92. PubMed

General references

  • Lone whale's song remains a mystery, New Scientist, issue number 2477, 11 December 2004
  • Frazer, L.N. and Mercado. E. III. (2000). "A sonar model for humpback whale song". IEEE Journal of Oceanic Engineering 25: 160–182. doi:10.1109/48.820748. 
  • Helweg, D.A., Frankel, A.S., Mobley Jr, J.R. and Herman, L.M., “Humpback whale song: our current understanding,” in Marine Mammal Sensory Systems, J. A. Thomas, R. A. Kastelein, and A. Y. Supin, Eds. New York: Plenum, 1992, pp. 459–483.
  • In search of impulse sound sources in odontocetes by Ted Cranford in Hearing by whales and dolphins (W. Lu, A. Popper and R. Fays eds.). Springer-Verlag (2000).
  • Progressive changes in the songs of humpback whales (Megaptera novaeangliae): a detailed analysis of two seasons in Hawaii by K.B.Payne, P. Tyack and R.S. Payne in Communication and behavior of whales. Westview Press (1983)
  • "Unweaving the song of whales". BBC News. 28 February 2005. http://news.bbc.co.uk/1/hi/sci/tech/4297531.stm. 

External links