encyclopedia of marine mammals || sound production

Sound Production1056

( R. Payne , ed. ) , pp. 81 – 87 . Westview Press , Boulder , AAAS Selected Symposia Series .

Noad , M. J. , Cato , D. H. , Bryden , M. M. , Jenner , M. N. , and Jenner , C. S. ( 2000 ). Cultural revolution in whale songs . Nature 408 , 537 .

Noad , M. J. , and Cato , D. H. ( 2007 ). Swimming speeds of singing and non-singing humpback whales during migration . Mar. Mamm. Sci. 23 , 481 – 495 .

Payne , R. S. , and Guinee , L. N. ( 1983 ). Humpback whale songs as an indicator of “ stocks ” . In “ Communication and Behavior of Whales ” ( R. Payne , ed. ) , pp. 333 – 358 . Westview Press , Boulder .

Payne , R. , and McVay , S. ( 1971 ). Songs of humpback whales . Science 173 , 585 – 597 .

Payne , K. , Tyack , P. , and Payne , R. ( 1983 ). Progressive changes in the songs of humpback whales ( Megaptera novaeangliae ): A detailed analysis of two seasons in Hawaii . In “ Communication and Behavior in Whales ” ( R. Payne , ed. ) , pp. 9 – 57 . Westview Press , Boulder .

Payne , K. P. , and Payne , R. S. ( 1985 ). Large scale changes over 19 years in songs of humpback whales of Bermuda . Z. Tierpsychol. 68 , 89 – 114 .

Tyack , P. L. ( 1981 ). Interactions between singing Hawaiian hump-back whales and conspecifi cs nearby . Behav. Ecol. Sociobiol. 8 , 105 – 116 .

Winn , H. E. , and Winn , L. K. ( 1978 ). The song of the humpback whale, Megaptera novaengliae, in the West Indies . Mar. Biol. 47 , 97 – 114 .

Sound Production ADAM S. FRANKEL

Most terrestrial mammals rely heavily on vision and smell. These senses are limited in water by the absorption of light and the slow physical movement of water. As a result,

marine mammals have evolved to use sound and hearing as their pri-mary means of communication and sensing their world.

This article briefl y reviews the basics of sound and the physical ways sounds are produced by marine mammals. The main focus is on characteristics of sounds made internally by marine mammals. Non-vocal sounds, such as tail slaps, are not treated in detail here. Certain species that stand out as particularly unusual or particularly well studied get special attention. Other species are treated in taxo-nomic groups, when their acoustic characteristics are similar or less well known. In addition, the odontocetes are organized according to their three main sound types: clicks, pulsed sounds and whistles.

I. Fundamentals of Sound Imagine throwing a rock into a calm lake. You can easily picture

the ripples, or water waves, that move out in an expanding circle. In these ripples, the water’s surface moves up and down, in a smooth progression from crest to trough. Sound waves are similar to these water waves. A sound wave is created by a structure that vibrates, such as a radio loudspeaker or our larynx. The crests of a sound wave are areas of high pressure, and the troughs are areas of low pressure. Like the water wave, there is a smooth progression between these areas of high and low pressure. A sound wave is a propagating (mov-ing forward) alternation of these areas of high and low pressure.

Several terms are used to describe the characteristics of sound. The amount of time it takes for a complete cycle between the high-est pressure of a sound wave to the lowest, and back to the highest,

is referred to as the period of the sound wave and is measured in sec-onds. The reciprocal of the period is called the frequency of the wave and measured in s � 1 , or more commonly Hertz (Hz). Frequency is a physical characteristic of sound. Our perception of frequency is known as pitch. Humans hear from about 20–20,000 Hz (or 20 kHz). Sounds below 20 Hz are termed infrasound, whereas those above 20 kHz are termed ultrasound.

Marine mammalogists often want to know the loudness of a sound, whether produced by a whale, dolphin, ship, or oil rig. The loudness, or amplitude , of a sound is described in decibels (dB). Decibels are defi ned as a ratio of measured sound pressure level to a reference sound pressure level. The reference sound pressure level in water is one microPascal ( μ Pa). Therefore, in-water decibels are expressed as XX dB re 1 μ Pa. Because sound amplitude decreases with distance, the standard method is to measure the sound level 1 m from the sound source. This measurement is known as the sourcelevel , and is expressed as XX dB re 1 μ Pa at 1 m. For example, fi n whale ( Balaenoptera physalus ) source levels have been measured at 171 dB re 1 μ Pa at 1 m ( Charif et al., 2002 ).

It is also important to remember that in-air and in-water decibels are not the same, due to different reference levels and the physical characteristics of air and water. Generally, adding 61.5 dB to an in-air measurement will convert it to an in-water measurement. Additional information and a technical discussion of sound level measurements can be found in other texts ( Hartmann, 2004 ; Richardson et al.,1995 ; Urick, 1983 ).

A sound is said to be frequency modulated (FM) when its fre-quency changes over time. Dolphin whistles are usually frequency modulated. Amplitude-modulated (AM) signals are those that change loudness, usually rapidly, over time. Many mysticete calls are amplitude modulated and can sound like growls.

A visual record of pressure versus time is known as a waveform . Animal sounds are more often represented as a spectrogram with frequency on the y-axis and time on the x-axis. Fig. 1 shows both the waveform and spectrogram of two blue whale ( Balaenoptera muscu-lus ) calls. The fi rst is an AM signal, and the second an FM signal. The AM signal shows individual amplitude pulses in the waveform, while the FM signal displays a smooth envelope (or waveform out-line). Note also that the AM signal shows the sidebands typical of an AM signal, while the FM signal has a downward sweep from about 20 to 15 Hz. Notice the “ extra lines ” above the main “ line ” of the FM signal. This is the lowest frequency or fundamental frequency contour. The additional “ lines ” above the fundamental frequency are harmonics, which are integer multiples (e.g., 2x, 3x, 4x) of the fun-damental frequency. They result from the physical characteristics of the sound-producing structure. Harmonics can occur only with FM calls and are strictly integer multiples of the fundamental frequency. The sidebands of AM signals may resemble harmonics, but are actu-ally the product of the rate of amplitude modulation.

Recently, marine mammal vocalizations have been found to contain spectral features called nonlinear phenomena. These are illustrated in Fig. 2 and include frequency jumps, subharmon-ics, biphonation, and deterministic chaos. Frequency jumps occur when the frequency of a signal changes almost instantaneously. Subharmonics are additional spectral bands that occur below the fundamental frequency. Animals are also capable of biphonation, or the production of two different harmonically unrelated sounds at the same time. There exists a phenomenon known as deterministic chaos that results from vocal folds oscillating asynchronously. While these signals appear random, they actually are deterministic and repeatable ( Fitch et al., 2002 ).

Sound Production 1057

II. Sound Production Mechanisms A. Terrestrial Mammals

When most terrestrial animals vocalize, the lungs push air through the larynx. The vocal folds (more commonly referred to as vocal cords) in the larynx open and close as the air rushes past them, breaking the exhalation up into a series of air puffs or pulses. The resulting undifferentiated sound then passes through the vocal tract of the throat, tongue, mouth, and lips. These structures can move to change the shape of the vocal tract, literally shaping the buzzing sound from the larynx into a vocalization. This mechanism is known as the source-fi lter model, where the vocal folds are the source of the sound and the vocal tract modifi es (or fi lters) the signal. The source-fi lter model traditionally has been applied to terrestrial animals, but recently has been employed to investigate sound production in pin-nipeds ( Sanvito et al., 2007 ).

B. Mysticetes Mysticetes also have a larynx with vocal folds that are believed to

be the source of their sound production ( Reidenberg and Laitman, 2007 ). The vocal folds in mysticetes are combined into a single U-shaped fold that is parallel to the airfl ow ( Fig. 3 ), in contrast to the perpendicular folds in terrestrial mammals. In addition, in mysti-cetes, a laryngeal sac is found underneath the larynx. The function of the sac is not known. It may serve as an additional acoustic radiating structure, or may help adjust air pressure in the laryngeal structure, or recycle air within the body of the whale. Observations of singing humpbacks ( Megaptera novaeangliae ) show that they do not exhale while singing, indicating a dependence on recycled air.

C. Odontocetes Odontocetes can produce clicks, pulsed sounds and whistles.

Clicks are often used for echolocation, as described elsewhere in the encyclopedia. Pulsed sounds and whistles are more likely to be used for communication. The production mechanism for these sounds has been the source of considerable debate.

Like mysticetes, delphinid odontocetes have a vocal fold structure in their larynx. These folds may be used in the production of some sounds ( Reidenberg and Laitman, 2007 ). However, it is known that clicks and most (and perhaps all) whistles are produced in the nasal region of the head ( Cranford, 2000 ). All odontocetes, except sperm whales, have a pair of structures known as the “ monkey lips ” /dorsal bursae (MLDB) complex located in the upper portion of their heads,

190180170

240230

1601501401301201101009080706050403020

10 20 30 40 50 1:00

1:10 1:20 1:30 1:40 1:50 2:00

0.00Hz

220210

Figure 1 Illustration of part of a blue whale ( Balaenoptera musculus ) song. The waveform is shown above and the spectrogram below. One can clearly see the series of loud pulses in the waveform of the fi rst sound, which is amplitude modulated (AM). These produced the sidebands seen in the spectrogram below. The second sound has a smooth envelope of its waveform. The spectrogram of the sound shows change with time, so this is a frequency modulated (FM) signal. The lines of energy above the bottom frequency contour are known as harmonics.

A B C D E

Figure 2 Examples of linear and nonlinear signals are shown: (A) typical linear signal (B) frequency jump, (C) subharmonics, (D) biphonation, and (E) deterministic chaos.

just below the blowhole ( Fig. 4 ). The MLDB complex consists of two lipid-fi lled sacs or bursae connected to the phonic lips or monkey lips that protrude into the nasal passage. The MLDB creates sound when air pushes past the phonic lips, which then open and slap shut, creat-ing vibration in the dorsal bursae. The air used to create the sound can either be returned to the lower nasal passage or released into the water. Whistling dolphins sometimes, but not always, release air as bubble streams from their blowhole ( Fripp, 2005 ).

The vibration generated by the MLDB is transmitted through the lipid-rich melon, which couples and focuses the sound into the water. In dolphins, the melon sits on top of the skull behind the rostrum ( Fig. 4 ). It also functions as an acoustic lens to focus clicks into a beam. This is similar in function to the focusing of light into a beam by the lens and refl ector of a fl ashlight. The beam pattern (or amount of focusing) is frequency dependent, with a more tightly focused beam at higher frequencies ( Au, 1993 ). Unlike other odon-tocetes, belugas are able to alter the physical shape of their melon, perhaps to adapt to sound transmission differences due to their movements between the open ocean and less saline estuarine waters ( Norris, 1968 ).

All odontocetes except the sperm whale ( Physeter macrocepha-lus ) have two MLDB complexes. It appears that they can operate these two structures independently, creating two different sounds simultaneously. Furthermore, in many delphinid species, one of these structures can be larger than the other, thus creating different spectral peaks ( Cranford, 2000 ).

The click production mechanism in sperm whales is related to the dolphins but is somewhat more complex. The huge head of the sperm whale almost certainly evolved as a sound production struc-ture. It appears that the spermaceti organ is the analog of the melon in dolphins, and is used to transmit and focus sound.

Clicks produced by sperm whales make multiple trips through the head ( Fig. 5 ) before being emitted into the water, resulting in a series of pulses that form individual clicks. First, the clicks are pro-duced near the front of the huge head in an organ called the museaude singe or monkey’s muzzle. A portion of that click goes forward directly into the water while the remainder moves backward, refl ect-ing off the skull into the water as a second sound pulse. Finally, part of this refl ected sound can make one more round trip, producing a third pulse of sound by refl ecting backward off the distal sac and for-ward again off the skull (Norris and Harvey, 1972; Møhl, 2001).

Esophagus

Vocal folds

Laryngeal sac

Trachea

Figure 3 Details of the mysticete larynx are shown. The vocal folds (in yellow) are parallel to the direction of airfl ow. The large laryngeal sac below the larynx, unique to the mysticetes, may function to recir-culate air, act as resonator, or modulate air pressure in the larynx . Redrawn from Reidenberg and Laitman, 2007 with permission .

Posterior bursaAnterior bursa

SkullAir space

Phonic lips

Figure 4 A diagram of the MLDB complex and sound production structures in the head of a dolphin. Redrawn from Cranford, 1999 with permission .

Figure 5 The anatomy of the sperm whale ( Physeter macroceph-alus ) head is shown. B, brain; BL, blowhole; Di, distal air sac; Fr, frontal air sac; Ju, junk; Ln, left naris; Ma, mandible; Mo, monkey muzzle/museau de singe; Ro, rostrum; Rn, right naris; So, spermaceti organ. Clicks are produced on the left at the monkey lips, propagat-ing in all directions. Sound that travels toward the skull is refl ected off the frontal air sac and then moves forward out of the head. Some of the sound can be refl ected again by the distal sac and frontal air sac again, resulting in a second round trip in the head before being emitted from the forehead. Redrawn from Madsen et al. (2002) with permission.

This pattern of pulses in the sperm whale click has been known for many years, but the relatively low intensity of the early record-ings lead some to doubt that clicks were useful for echolocation. However, it has recently been shown that sperm whales can produce directional high intensity clicks that are suffi ciently intense for use in echolocation and foraging (Møhl et al., 2000; Miller et al., 2004 ).

D. Sirenians and Carnivores [Polar Bear ( UrsusMaritimus) and Pinnipeds]

Although sound production in sirenians is poorly studied, it is known that manatees ( Trichechus spp.) and dugongs ( Dugong dugon ) possess a rich repertoire of sounds. Both sirenians and polar bears may produce sound with their larynxes, similar to terrestrial mammals.

Sound production mechanisms in pinnipeds are not well known. When in air, most pinnipeds exhale while vocalizing and probably use their typical mammalian larynx to produce sounds ( Tyack and Miller, 2002 ). However, other sound production mechanisms are found in pinnipeds. For example, male hooded seals ( Cystophora cristata ) have a specialized nasal hood and septum that can be partially extruded out a nostril and then infl ated. By alternately defl ating and infl ating this apparatus, they produce a variety of sounds. Walruses ( Odobenus rosmarus ) also have the ability to create a variety of airborne sounds such as whistles, made by blowing air through the lips, and gong-like sounds, made with their pharyngeal sacs.

Underwater, pinnipeds rarely exhale while vocalizing, indicating that air is shunted between the lungs and mouth/nasal structures. Rather than vocal folds in the larynx, they may use vibrating mem-branes in the trachea to produce sound underwater. Underwater observations of pulsations in the chest or throat seem to confi rm a tracheal mechanism for underwater sound production in many phocids ( Tyack and Miller, 2002 ), as is likely for the long trills of the bearded seal (Erignathus barbatus).

III. Characteristics of Vocalizations by Groups and Selected Species

A. Pinniped Sounds Acoustic signal structure varies widely within the 33 species of

pinnipeds ( Schusterman and Van Parijs, 2003 ). All pinnipeds are amphibious to some degree, and how they proportion their activities on land and at sea signifi cantly affects their social system, and there-fore their acoustic behavior.

Most of the signals of aquatic mating species occur in the water, whereas terrestrial breeding pinnipeds produce a wide variety of vocalizations while hauled out. These signals are often loud, direc-tional, broadband and highly repetitive ( Schusterman and Van Parijs, 2003 ).

Aquatic mating species have evolved a wide variety of signals that are used during the mating season. A review of two phocid species [bearded and Weddell ( Leptonychotes weddellii ) seals], for which there are year-round recordings, found a strong peak in the rate of vocal production associated with breeding ( Stirling and Thomas, 2003 ). Bearded seals became silent after breeding, while Weddell seals continued to vocalize at a low rate, suggesting that they may have been defending breathing holes. This temporal pattern of vocalization indicates, but does not confi rm, that these signals are used to attract mates ( Van Parijs, 2003 ).

One notable aspect of life history in many pinniped species is the need for the mother to leave her offspring to forage during lactation. The use of acoustic signals to help reunite mother and pup has been

demonstrated in both otariids and phocids. Otariid mothers regularly leave their pups to forage during lactation. This behavior has led, in part, to otariid pups and mothers evolving individually distinct and stereotyped vocal signals that facilitate reunion when the mother returns. These calls tend to be low frequency and about a second in duration. Within a species, there can be signifi cant differences in the fundamental frequency, amplitude modulation and frequency modu-lation that make the calls distinguishable.

Phocid mothers do not regularly leave their pups during lactation, and their calls are not as individually distinctive. Species with very short lactation periods have no individual recognition mechanisms. Hawaiian monk seals ( Monachus schauinslandi ) are an extreme case. Mothers nurse indiscriminately and do not have individual recogni-tion ability. In general, the amount of individual information in pin-niped calls and recognition ability is greater in polygynous societies, those that have a longer lactation period and more crowded breed-ing colonies ( Charrier and Harcourt, 2006 ).

1. Phocids Ringed seals ( Pusa hispida ), like many seals, were long thought to be silent while underwater. However, they are now known to produce at least six types of underwater calls. These include clicks, burst pulses, knocks, chirps, yelps and a variety of low-frequency calls similar to those produced in air ( Kunnasranta et al., 1996 ). Clicks are very short, lasting between 6 and 8 msec with energy between 2 and 6 kHz. Burst-pulse sounds are low frequency and narrowband, typi-cally composed of a short sequence of pulses ( � 5 msec). Knocks are low-frequency sounds, from 150 Hz to 2 kHz that occur in a sequence of increasing frequency pulses. Each knock lasts 40–80 msec, and the entire sequence lasts between 500 and 900 msec. Chirps are FM tonal calls, descending from 1,000 to 500 Hz and lasting between 100 and 300 msec. Yelps show slight frequency modulation around a fundamen-tal frequency of � 1 kHz, and last 100–200 msec ( Kunnasranta et al.,1996 ). The proportion of calls recorded in the Arctic varied seasonally, consistent with a reproductive function ( Stirling, 1973 ).

Bearded seals are an aquatic mating species with an extensive repertoire composed of four basic call types: trill, moan, sweep and ascent ( Risch et al., 2007 ). Considerable variation exists within each of these call types. Trills are one of the most distinctive signals pro-duced by marine mammals. They are usually long downsweeps, but some variations include a near-constant frequency contour or alternat-ing increases and decreases of frequency. Typically they start between 3 and 6 kHz, lasting from 30 sec to more than a minute and are charac-terized by repeated frequency jumps during the signal. In some popu-lations, the long trill is followed by a rapid upsweep to 3 kHz that lasts 1–2 sec ( Fig. 6 ).

Moans are characterized by a short duration, low frequency com-position, and lack of frequency modulation. Sweeps resemble a short trill, typically with a rapid decrease in frequency in the second half of the signal. Sweeps are not produced by all populations. Ascents are relatively simple frequency upsweeps lasting from 6 to 25 sec; they are found in those populations that lack sweeps.

The vocalizations of bearded seals show signifi cant variation between individual males of the same populations, as well as signifi -cant differences between different populations ( Risch et al., 2007 ). They are thought to function as advertisement displays during the mating season.

Hooded seal sounds can be grouped into three major classes. Two of these are produced by normal vocal mechanisms. The third is produced with the hood and septum, a set of specialized anatomical structures. The most common calls are produced both in air and in water. They are pulsed and rarely frequency modulated, with energy

ranging from 500 Hz to 6 kHz.These are used in a variety of circum-stances, including male displays, female responses, and interactions between females and pups. The second type, growls or roars, appear to be used as low-level threats by both males and females fi ghting with other males. The third type of signals, produced by the infl ation and defl ation of the hood and septum, are short-duration, broad-band with rapid onsets, and little or no frequency modulation. It is possible that only males make these sounds, described as “ bloops ” , “ wooshes ” , “ metallic pings ” , “ clicks ” , and “ knocks ” ( Ballard and Kovacs, 1995 ).

Harp seals ( Phoca groenlandicus ) aggregate at the ice edge in March in the Northwest Atlantic. At least 19 different call types have been described for this species, ranging from a nearly pure sine wave to pulsed sounds, high-frequency chirps, “ broadband warbles, ” trills, squeaks, and grunts ( Terhune, 1994 ). The maximum source level of these calls is between 135 and 140 dB re 1 μ Pa at 1 m. Harp seals also produce clicks that are about 25 dB louder than their other calls. Call types have been shown to be stable over a period of tens of years ( Serrano and Terhune, 2002 ). The calls may help individuals locate the herd, and once in the aggregation, may be used to fi nd a mate. Comparisons of different breeding aggregations found many shared calls, but some that were unique to particular breeding areas, sug-gesting that the populations may be reproductively isolated.

Ribbon seals ( Histriophoca fasciata ) are a close relative of harp seals. However, there is only one report on their vocalizations, which describes them as “ puff sounds ” and frequency downsweeps ( Watkins and Ray, 1977 ). Downsweeps were broken into three cat-egories. Long downsweeps descend from as high as 7100 to 2000 Hz and last up to 4.7 sec. Medium sweeps range from 5300 down to

100 Hz, and last up to 1.8 sec. Finally, short sweeps last less than a second and descend from 2000 to 300 Hz. Puff vocalizations are broadband, below 5 kHz, and last also less than a second.

Harbor seals ( Phoca vitulina ) have a mating system with a low degree of polygyny. Females have not been found to vocalize under-water while males produce fi ve types of underwater acoustic displays: roar, bubbly growl, grunt, groan, and creak ( Hanggi and Schusterman, 1994 ). Roars are one of the primary vocalizations of male harbor seals, lasting between 2 and 11 sec, with energy between 20 and 1550 Hz. There is good evidence that the frequency of roars varies between individual males. Roars have been shown to function in territorial behavior ( Hayes et al., 2004 ). Bubbly growls are another long vocali-zation, lasting between 1 and 8 sec and sounding as if the seal were blowing bubbles underwater. Grunts are short tonal calls from 100 to 4000 Hz lasting less than a second. Groans are a longer version of grunts, lasting between 1 and 5.5 sec. Creaks are tonal calls lasting up to 6 sec with rich harmonic content.

Spotted seals ( Phoca largha ) in captivity produced six types of underwater vocalizations: “ growls ” , “ drums ” , “ snorts ” , “ chirps ” , “ barks ” and “ cranky door U ” ( Beier and Wartzok, 1979 ). These vocal-izations include pulsed and tonal signals. The sounds ranged from 500 Hz to 3.5 kHz and durations from 19–400 msec. Males produce signals at a rate approximately 2.5x times that of females, again sug-gesting that males are producing signals as part of mating behavior.

Gray seals ( Haliochoerus grypus ) recorded in Canada produce calls that have been classifi ed into seven types ( Asselin et al., 1993 ). The most common is a short duration call ( � 0.2–1.0 sec) that begins with a near-constant low frequency component that then sweeps upward sharply in frequency to about 3 kHz. The second most

0.2000.000

5 10 15 20 25 30 35 40 45 50 55kHz

Figure 6 The long downward trill and rapid upsweep of a bearded seal from Alaska are shown in this spectrogram.

common call ranges from 0.1 to 2.9 sec in duration, and is composed of a gradual low-frequency downsweep followed by a second compo-nent that began at a slightly higher frequency, fi rst sweeping up and then down. Other call types produced much less frequently include growls, knocks, clicks, roars and a pulsed signal called a “ trot ” ( Page et al., 2002 ).

Elephant seals ( Mirounga spp.), especially males, are known to use acoustic signals in agonistic encounters. They mate on land where males compete for dominance and access to females. Males use threat displays and fi ghts to establish dominance. Male elephant seals make three main types of calls during AGGRESSION: “ snores ” , “ snorts ” , and “ clap threats ” . Snores are used as a low-intensity threat. Dominant males snort more aggressively when approached by a challenging male. Snorts range between 200 and 600 Hz. The clap threat ranges up to 2.5 kHz ( Sandegren, 1976 ; Shipley et al., 1981 ; Shipley et al., 1986 ). It is thought that in-air threat calls produced by males are also transmitted through the ground, and can elicit responses from other elephant seals ( Shipley et al., 1992 ). Females produce a low-frequency “ belch roar ” in aggressive situations and a 500 Hz–1 kHz bark to attract the pup ( Bartholomew and Collias, 1962 ).

Recently the acoustic characteristics of these signals have been compared to the physical attributes of the signaler. While there is only a weak relationship between body size and signal loudness, the signal structure accurately represents the age, size, and resource-holding potential of the signaler ( Sanvito et al., 2007 ). Therefore, in many cases individuals can assess the relative dominance of each other and resolve the interaction without fi ghting.

Elephant seals are known to make underwater sounds, but these remain poorly described ( Poulter, 1968 ).

Monk seals ( Monachus spp.) are not a very vocal species. They do produce in-air vocalizations composed of soft “ liquid bubble sounds ” , guttural expirations, roars and a “ belch-cough ” . Most of the energy of these calls is below 1 kHz ( Miller and Job, 1992 ).

Weddell seals are a very vocal species. Males produce long com-plex displays that are known as song. Signals appear to vary between different geographic areas. One of the best descriptions of song is based on the Davis Straight population, where seals produced ten different calls consisting of roars, whistles and trills.

Roars can last over 5 sec and vary in frequency from a few hundred to several thousand Hz. Whistles can be both upswept and downswept, ranging to 10 kHz or higher. Trills, produced only by males, may be the most distinctive Weddell seal vocalization ( Oetelaar et al., 2003 ). Trills are long downswept FM calls, beginning above 10 kHz and sweeping down to 1–2 kHz, producing a curved spectrogram. Songs appear to have individually distinct variations in their basic sound units and seem to function in both territorial defense and mate attraction ( Terhune and Dell’Apa, 2006 ).

Leopard seal ( Hydrurga leptonyx ) vocalizations show consid-erable structural variability. Their calls include low-frequency tonal calls, narrowband and wideband high-frequency pulses, and FM calls ranging from 50 Hz to 8 kHz. Males in Prydz Bay, Antarctica, produce a lengthy ordered pattern of fi ve different calls that appears to func-tion as a reproductive display. The structure of these signals varies between individuals ( Rogers and Cato, 2002 ). There is also consid-erable geographic variation in the signals produced by males of dif-ferent populations ( Thomas and Golladay, 1995 ). Females in estrus are also known to produce a collection of signals, collectively known as broadcast calls that may serve to indicate their reproductive con-dition ( Rogers et al., 1996 ). Hauled-out leopard seals that were approached by a researcher made explosive, broadband vocalizations

termed “ blasts ” and “ roars ” that may have been used as threats or territorial calls.

Crabeater seal ( Lobodon carcinophaga ) vocalizations are poorly known. Only one vocalization has been reported. The groan-like sig-nal had a mean duration of 2.12 sec with most energy below 1.5 kHz ( Stirling and Siniff, 1979 ).

Ross seal ( Ommatophoca rossii ) in-air vocalizations include 1–1.5 sec long FM upsweeps and downsweeps between 100 and 1,000 Hz. They also produce sequences of 5–12 short frequency down-swept pulses, each lasting 50–100 msec. Sounds produced in water are similar to in-air sounds, except that the frequency range is wider and the longer FM calls possess sidebands not present in air ( Watkins and Ray, 1985 ).

2. Otariids The eared seals appear to lack the complex social signals of many phocids. This is probably because phocids tend to mate in the water, and sounds are often, although not always, related to social/sexual interaction. Otariids, however, tend to mate on land, and they are in large part relatively quiet in the sea.

California sea lions ( Zalophus californianus ) make bark-like sounds, groans, and grunts in air. The sound of a group of hauled-out California sea lions is loud and far reaching. Barks tend to have most energy below 2 kHz. These sounds and other interactions help produce the structural organization of sea lion society on a beach or headland. Sea lions also bark underwater, in similar fashion as in air ( Schusterman and Balliet, 1969 ).

Galapagos fur seals ( Arctocephalus galapagoensis ) have been recorded making few vocalizations while at sea. These include a long growl, lasting 8 sec and composed of a series of discrete low-frequency sounds with energy less than 1 kHz. They also produce knocks, which are single short broadband pulses lasting less than 100 msec with energy above 2 kHz ( Merlen, 2000 ).

South American sea lion ( Otaria fl avescens ) sound production differs between males and females. During the breeding season, males produce four types of vocalizations: growls, barks, high-pitched calls (HPC), and exhalations, while females produce grunts. Mothers, pups, and yearlings all produce “ primary ” calls that are used for female–offspring interactions (Fernández-Juricic et al ., 1999). Growls are AM calls used during male–female interactions, lasting about one second, with energy between 200 and 2,000 Hz. Barks are a series of short, 0.2 sec, low-frequency pulses produced by males during low-level agonistic interactions. HPCs are short, � 0.4 sec, FM calls with funda-mental frequencies between 300 and 500 Hz. Produced during agonis-tic encounters between males, they are highly directional, suggesting that they can be directed toward specifi c individuals. Females can pro-duce low intensity, low frequency, 490 Hz, and brief, � 0.4 sec, calls referred to as grunts usually made during female–female agonistic encounters.

South American fur seals ( Arctocephalus australis ) make at least 11 types of calls, which appear to fall into 4 functional classes: investi-gative, threat, submissive, and affi liative ( Phillips and Stirling, 2001 ). Barks are short broadband pulses that occur in a sequence up to sev-eral minutes in duration. Barks are used for non-agonistic investigation of other individuals. “ Threat calls ” are composed of several sounds produced by forceful inhalation or exhalation. Call amplitude can be changed, with louder calls indicating a higher threat level. Threat calls are all amplitude modulated with energy between 400 and 700 Hz. “ Submissive calls ” are FM tonal calls between 600 and 1600 Hz last-ing about a second. Finally, the affi liative calls include pup-attraction calls that last up to 2 sec. These are composed of a pulsed component followed by a tonal component between 700 and 1000 Hz, ending with

a downsweep. Female-attraction calls are similar in structure, though they may have more frequency modulation. Both attraction calls have a large degree of inter-individual variability.

Australian fur seals ( Arctocephalus pusillus ) produce in-air barks during male–male interactions. Each bark is a short call, � 0.25–sec, with multiple harmonics extending to about 5 kHz and is typically pro-duced in a series. There is enough individual variation to indicate that males may recognize each other with their barks ( Tripovich et al., 2005 ).

3. Odobenid Walrus adults use roars, grunts, and guttural sounds as threats while hauled out ( Miller, 1985 ). Roars are long, loud mostly low-frequency calls that last a second or more. Grunts vary greatly in amplitude, last between 100 and 400 msec and range from 50 to 250 Hz. The most common acoustic threat is the guttural sound, a series of low frequency, wideband pulses ranging from 13 Hz to 4 kHz. Walruses also bark, usually in a series of short, FM calls ranging from 90 to 260 msec in length and between 300 and 500 Hz. Adult barks indicate submission; louder barking may indicate greater submission. Calves bark in a wide variety of situations. For example, calves separated from their mothers bark loudly and then may con-tinue to bark softly once the two are rejoined. As the calf matures, its bark changes, gradually becoming a longer single call, with both fre-quency and amplitude modulation. While females do not call to attract the calf, they do produce a short, soft contact call when mother and calf are in close proximity. The call is usually frequency modulated, either as a downsweep or as an alternation of up-and-down sweeps.

Male walruses sing on the mating grounds. Songs are loud, repeti-tive, and stereotyped sequences of pulsed sounds with bell-like sounds interspersed between them ( Sjare et al., 2003 ). These animals make two types of pulsed sounds: the intense “ knock ” and the less intense, quickly repeating “ tap ” . Knocks range between 0.2 and 8 kHz and are produced at a rate of 1–3/sec. Taps are produced at a higher rate, 10/sec, and range in frequency from 0.2 to 4 kHz ( Stirling et al., 1983 ). As a courting display, males also make a gong-like sound, both in air and underwater, infl ating their throat pouches, sometimes striking their throat with their fl ippers to augment the sound ( Tyack and Miller, 2002 ). Male walruses also make aggressive nonvocal clacking sounds with their teeth.

B. Mysticete Sounds Mysticetes produce a wide variety of sounds, from the blue

whale’s 7 Hz infrasonic pulses to the humpback whale’s songs whose harmonics can range to at least 24 kHz. Individual signals can last less than a second or as long as 30 sec or more. The range of signal types

varies from simple growls to loud complex modulated high frequency calls. Four mysticete species are now known to sing: humpback, bowhead ( Balaena mysticetus ), blue and fi n whales. Song is typi-cally defi ned as a repetition of patterned signals. Humpback whale song was fi rst described scientifi cally in the early 1970s. Bowhead song was recognized in the 1980s. Blue whale song was described in the 1990s and fi n whales were recognized as singers in the early 2000s.

Humpback whale songs were fi rst described by Roger Payne and Scott McVay in 1971. Only males sing, primarily on the mating grounds in winter, and it is surmised that song is a mating display; intersexual, for males to attract females; intrasexual, as a male domi-nance display; or both ( Frankel et al., 1995 ). Humpback whale songs have a hierarchical structure, from the shortest utterance to long bouts of singing that can last for days. Individual calls (somewhat analo-gous to musical notes) are referred to as song units. These units are repeated and combined to form phrases that are then repeated to form longer themes. A song is typically composed of 4–12 themes. Songs can last from 5 to 30 min in length before beginning again. Individual humpbacks are known to sing for as short as a few minutes and as long as 48 h or more. Song units are highly variable, including upsweeps, downsweeps, AM units and complex FM sweeps ( Fig. 7 ). Song units range widely in frequency as well, from fundamental frequencies of about 20 Hz to harmonics reaching 24 kHz or higher. Individual units can last from fractions of a second to several seconds.

Individual whales slowly change the structure of their songs over time ( Payne et al., 1983 ). To illustrate this, consider a theme with two upsweeps and a growl. One type of change would be the addi-tion of a third and then a fourth upsweep. Usually, these changes occur gradually, over a period of about one month. However, the pace of change in song structure is variable as well. In some years the song changes slowly and in other years it evolves rapidly.

Another unique feature is that all humpback whales of a popula-tion typically sing essentially the same song, with only minor varia-tions ( Payne and Guinee, 1983 ). It is not known how this uniformity is maintained while the song itself keeps changing. However, it is likely that whales within a discrete area pay attention to each other’s song, and some whales copy others. Thus humpback whale song rep-resents an example of cultural evolution.

Once they have evolved, it seems that individual themes are not reused. All themes are created de novo ( Payne and Payne, 1985 ).The longest that an individual theme has been known to persist was 5 years ( Eriksen et al., 2005 ).

Song sessionDurations

∼12 min

Theme 6∼2 minTheme 5Theme 4

Phrase Phrase Phrase Phrase Phrase Phrase ∼15 Sec∼7 Sec∼1 Sec

Subphrase Subphrase Subphrase Subphrase Subphrase Subphrase Subphrase Subphrase Subphrase Subphrase Subphrase

(3 units) (6 units) (4 units) (3 units) (4 units) (4 units) (4 units) (4 units) (4 units) (2 units) (9 units)

0 15 30 45 60 75 90 105 120Seconds

Figure 7 The hierarchical structure of humpback whale ( Megaptera novaeangliae ) song. Redrawn from Payne et al. (1983) with permission .

While most song is produced on the wintering or breeding grounds, it is also heard during migration and on the summer feed-ing grounds, albeit at a reduced rate ( Clark and Clapham, 2004 ; Gabriele and Frankel, 2002 ).

Humpback whales on the breeding grounds also produce a rich repertoire of non-song vocalizations, generally termed social sounds. Social sounds can be thought of as a subset of the song units, uttered in a non-patterned fashion. These sounds appear to be used by males as acoustic threat displays in conjunction with visual displays and direct physical contact ( Silber, 1986 ). Humpback calves are also known to produce short, low-frequency calls, although the function of these calls remains unknown ( Zoidis et al., 2008 ).

Finally, humpbacks produce vocalizations during feeding. One call is made during a foraging strategy known as social lunge feeding. This entails a group of 6–12 or more humpbacks all vertically lung-ing through the surface of the water in a coordinated fashion. The accompanying call is a sequence of “ cry ” vocalizations. The cry typi-cally begins with a short upsweep, followed by a long near-constant frequency tone, fi nishing with a short downsweep. There is little variation in the frequency of the call within a sequence, but there is strong variation between different sequences, suggesting the presence of individual variation ( Cerchio and Dalheim, 2001 ). In experiments, these calls were played to herring, which responded by fl eeing, sug-gesting that the most likely function of the call is prey manipulation ( Sharpe, 2001 ).

More recently, humpbacks foraging in the Northwest Atlantic were found to produce click trains and buzzes while feeding at night. Although these signals are reminiscent of odontocete echolocation signals, the function of these “ megapclicks ” has not yet been estab-lished ( Stimpert et al., 2007 ).

Bowhead whales were discovered to sing during the acoustic pop-ulation census of bowhead whales during the spring migration from the Bering Sea to the Chukchi Sea. Songs are usually heard more often at the beginning of the migration and less so at the end. This suggests that most of the singing occurs in the Bering Sea in winter. More recently, songs have also been recorded from the Davis Strait population in Greenland between February and May ( Outi et al., 2007 ).

Song notes are usually longer than non-song moan and grunt-like calls. Bowheads sing between one and three themes, most often two. Unlike humpback whales, bowhead songs regularly show substan-tial change in structure in successive years. Within a year, all whales within a population sing the same basic version of song, but there is considerable inter- and intra-individual variation. Most of the sound energy of bowhead calls and songs falls below 1000 Hz. The songs are frequently composed of both AM and FM components. Bowhead whales produce fewer units and in a narrower frequency range than humpbacks, yet their signals have great variation in tone, resulting in a wide variety of different sounding song notes.

In addition to songs, bowheads produce a host of calls. There are two main groups: the simple, low-frequency FM calls and complex calls. These FM calls can be categorized by their FM contours, i.e., upsweeps, downsweeps, constant, and infl ected contours. FM calls are almost always less than 400 Hz in frequency. The complex calls have been described as pulsive, pulsed tonal, and high. High calls have frequencies above 400 Hz and sound like a whine. The pulsed tonal is a combination of both frequency and amplitude modulation. Pulsive calls are a mixture of pulses, with both frequency and ampli-tude modulations. Pulsed tonal calls are often below 400 Hz, but pul-sive calls can exceed 1000 Hz.

Migrating bowheads will sometimes produce calls for periods ranging from a few minutes to several hours. These are often made

in the context of whales counter-calling with each other. Thus it has been suggested that these calls are used to maintain group cohe-sion. They may also be used to help orient themselves in ice fi elds. A group of whales was observed approaching a large block of ice. The fi rst whales to encounter the ice only swam around it when they were very close. The following whales defl ected much ear-lier, suggesting that they were listening to the echoes of the early whales and using the acoustic information to avoid the ice ( George et al., 1989 ).

Fin and blue whales are the two largest species of extant ceta-ceans. They both produce the loud and well-known low frequency 20 Hz sounds that are capable of traveling over great distances. In fact, their sounds have been heard at distances covering at least sev-eral hundred kilometers. It has been hypothesized that, at least prior to the rise of motorized shipping, whales could hear each other over ocean basin extents ( Payne and Webb, 1971 ). This is possible due to the deep sound channel that propagates low-frequency sound extremely well.

While similar in frequency, blue and fi n whale calls differ in length. Most fi n whale sounds last about 1 sec, whereas many blue whale signals can be up to 30 sec.

The frequency range of fi n whale calls varies in different ocean basins. Most calls from the Atlantic are 1 sec downsweeps from 23 to 18 Hz while those in the Gulf of Mexico sweep down from 42 to 20 Hz ( Thompson et al., 1992 ). These 20 Hz pulses often occur as a long, regularly patterned series of calls. The interval between pulses typically ranges from 6 to 37 sec. In addition to the 20 Hz pulses, fi n whales also make tonal pulses at higher frequencies.

In temperate waters, fi n whales produce regular sequences of short downswept pulses from about 30 to 15 Hz, predominately dur-ing winter. This temporal pattern suggests that these signals may serve a reproductive function ( Watkins et al., 1987 ). Furthermore, only males produce these long patterned sequences, now described as song ( Croll et al., 2002 ). While pulses occur year round, they are less patterned during the non-winter months. It may be that fi n whale song is used for reproduction while the less patterned calls may serve another function ( Moore et al., 1998 ).

Male blue whales also produce songs throughout the year ( McDonald et al., 2001 ; Oleson et al., 2007 ) and it is surmised that they may also serve as a reproductive display. There are at least nine, and probably more, song populations. Songs within a popula-tion appear to have a stable structure while song structures differ between populations ( McDonald et al., 2006 ). Some of these song populations have only simple tonal calls, while others exhibit more complex songs that include pulsed as well as tonal units.

As an example, the song of the North Eastern Pacifi c blue whale population contains both tonal and pulsed components: the pulsed A call, tonal B call, an A–B combination, and downsweeps known as D calls (Thompson et al. 1996; McDonald et al. 2001 ). The amplitude-modulated A call typically lasts 17 sec and has a fundamental fre-quency of 16 Hz. The frequency-modulated B call lasts about 19 sec, sweeping down from � 18 to � 15 Hz and often has strong harmon-ics. The D call is a short downsweep lasting a few seconds that starts at about 90 Hz descending to about 30 Hz.

Song has been recorded solely from traveling animals. Individual ( i.e., non-song) A or B calls were produced from animals in a variety of behavioral states ( Oleson et al., 2007 ), suggesting different func-tions for non-song calls. Blue whales in the Eastern Tropical Pacifi c have a higher rate of B call production when their vertically migrat-ing prey is near the surface, suggesting a possible foraging func-tion for the B calls ( Stafford et al., 2005 ). Similarly, the D calls are

produced by both sexes, frequently during foraging ( Oleson et al.,2007 ).

Minke whales ( Balaenoptera acutorostrata ) are known to produce a variety of different calls with a wide frequency range. These include clicks, tonals and FM signals. Minke signals also have signifi cant geo-graphic variation in their call structure. Because minke whales are often diffi cult to observe in the wild, it has taken many years to associ-ate them with their sounds. Some have only been described in recent years, others almost certainly remain undiscovered.

One notable sound type is the pulse train. These are a repetitive series of pulses, which can either be a narrow-bandwidth (e.g., 80–140 Hz) “ growl ” , or a wider bandwidth “ thump ” ranging from 100 to 800 Hz ( Winn and Perkins, 1976 ). Thump trains can last over a minute.

Australian dwarf minke whales make a vocalization so unu-sual that it has been termed the “ Star Wars ” call ( Gedamke et al.,2001 ). This call consists of a series of three 100 msec pulses rang-ing between 50 Hz and 9.4 kHz. These pulses are produced simul-taneously with harmonically unrelated low frequency, AM pulses between 50 and 750 Hz. Following the pulses, the whale produces a pulsed tone at 1.8 kHz along with a tonal call at 80 Hz. The tonal call shifts up to 140 Hz as the fi nal component of this complex set of vocalizations. The communicative function is unknown.

North Pacifi c minke whales were recently discovered to be the source of the “ boing ” sound ( Rankin and Barlow, 2005 ). Boings have been known and recorded since the 1950s ( Wenz, 1964 ). Those recorded in the Eastern Pacifi c are longer and have a lower pulse repetition rate than those recorded in the Central Pacifi c ( Rankin and Barlow, 2005 ).

Sei whales ( Balaenoptera borealis ) rarely have been recorded. In the Northwest Atlantic they are known to produce two phrases that are each 0.5–0.8 sec long. The phrases are composed of 10–20 FM sweeps between 1.5 and 3.5 kHz, each 30–40 msec in duration ( Knowlton et al., 1991 ; Thompson et al., 1979 ) with an interval of 0.4 and 1 sec between the two phrases. Recordings off Cape Cod found low frequency downsweeps from 90 to 40 Hz lasting a few seconds in duration ( Esch et al., 2007 ). Sei whales in Antarctica produced low-frequency tonal calls, FM sweeps, and broadband signals. The tonal and FM sweeps ranged from approximately 100 to 1000 Hz, lasting from 0.2 to 1.8 sec and often including a frequency jump. The source levels for these calls ranged from 147 to 156 dB re 1 μ Pa at 1 m ( McDonald et al., 2005 ).

Bryde’s whales ( Balaenoptera edeni ) recorded from the Gulf of California contained short low-frequency moans between 70 and 245 Hz and lasting between 0.2 and 1.5 sec. Source levels range between 152 and 174 dB re 1 μ Pa at 1 m ( Cummings et al., 1986 ). A captive juvenile Bryde’s whale produced a pulsed moan, ranging between 100 and 900 Hz and between 0.5 and 51 sec in duration. These moans were similar, though longer, than those recorded in the wild. Finally, wild calves have been recorded making a series of discrete pulses between 700 and 900 Hz ( Edds et al., 1993 ). Bryde’s whales in the Eastern Tropical Pacifi c produce at least six different call types. Most of these are lower in frequency than previous recordings, between 20 and 60 Hz, with one type being a frequency downsweep from 207 to 75 Hz. Durations ranged from 1.1 to 4.9 sec ( Oleson et al.,2003 ). Bryde’s whales off New Zealand also produced low-frequency calls, predominately a broadband pulse followed by a 25–22 Hz down-sweep and a 5 sec long 22 Hz tonal call ( McDonald, 2006 ).

Right whales ( Eubalaena spp.) from the southern hemisphere produce an “ up ” call, an upsweep from 50 to 200 Hz that lasts for about a second. This call appears to be used to bring individuals

together, because calling stops once the whales rejoin. “ Down ” calls are downsweeps from 200 to 100 Hz that are also about a second in length. They may serve to maintain acoustic contact, if not physical proximity. “ Constant ” calls have a nearly constant frequency between 50 and 500 Hz and are 0.5–6 sec in duration. These calls are typically produced by whales that are simply swimming or engaged in a low level of activity ( Clark, 1983 ).

Three call types are associated with surface-active or sexually active right whales: “ High ” calls are higher in frequency, up to 1 kHz, often with rapid frequency modulations, notably a downsweep at the end. These typically last 0.5–2.5 sec. “ Hybrid ” calls are similar to the high call, but then end with an AM pulse. “ Pulsive signals ” are mostly broadband AM signals ( Clark, 1983 ).

Sounds made by North Atlantic right whales ( Eubalaena glacialis ) are similar to their southern counterparts, with one known exception. North Atlantic right whales also make a short broadband vocalization called the “ gunshot ” . Produced only by males, gunshots may be used to attract females. Alternatively, they may be used as an agonistic sig-nal directed toward other males, or may serve both functions ( Parkset al., 2005 ). North Pacifi c right whales are only known to make calls similar to the southern right whale’s up, down, and constant calls.

Right whales feeding with their upper jaw raised above the water’s surface can produce a nonvocal sound called “ baleen rattle ” . As water fl ows through the lower portion of the baleen plates, they apparently rattle together, producing a series of short broadband pulses between 1 and 9 kHz, with most of the energy between 2 and 4 kHz. This sound is audible both in air and underwater, and may be simply a by-product of feeding ( Watkins and Schevill, 1976 ).

Pygmy right whales ( Caperea marginata ) have only recently been recorded. A juvenile found in a harbor produced only one sound type. It was a short tonal downsweep that began between 90 and 135 Hz and swept down to 60 Hz. Pulses lasted between 140 and 225 msec in duration and were separated by intervals of 430–510 msec. Source levels were estimated between 153 and 167 dB re 1 μ Pa at 1 m. These calls were very simple and their function remains unknown ( Dawbin and Cato, 1992 ).

Gray whales ( Eschrichtius robustus ) most frequently produce sounds referred to as “ knocks ” and pulses. These range in frequency from 20 Hz to 3 kHz. Gray whales are fairly vocal while feeding, rela-tively quiet while migrating, and the most vocal during mating activi-ties. The source levels of gray whale vocalizations range between 167 and 188 dB re 1 μ Pa at 1 m ( Petrochenko et al., 1991 ).

Six major signal types have been recorded from gray whales on the mating grounds: a series of 2–30 metallic-sounding pulses; a sin-gle pulse lower in frequency and longer in duration than the fi rst; a relatively low frequency and long duration “ moan ” ; short “ grunts ” ; a loud “ bubble blast ” produced by releasing a large amount of air underwater; and fi nally, a sixth sound type produced by the exhala-tion of a series of bubbles ( Dahlheim et al., 1984 ). Recordings made on summer feeding grounds contained three signals similar to those heard on the wintering grounds ( Moore and Ljungblad, 1984 ).

C. Odontocete Sounds The toothed whales, or odontocetes, are vocal animals par excel-

lence . They probably all produce clicks for echolocation, and many produce complicated sets of pulsed sounds and whistles, the latter two for communication. Not all odontocetes make all of these sound types, and there are signals that cross categorical bounds and others, that defy categorization. Nevertheless, these three broad categories can be useful and descriptive. Rather than attempt to consider the

signals of each odontocete species individually, this section will focus on the three sound types, with specifi c examples provided for each.

1. Click Sounds Most of the odontocetes are known to produce clicks. In many (if not all) species, these clicks are used for echolo-cation. An echolocating animal produces a click that travels to and refl ects off a target, such as a prey item. The amount of time elapsed between click production and echo reception (i.e., the two-way travel time) provides a measure of the distance to the target. Many spe-cies are also able to determine direction to the target. The clicks are usually produced at an interval greater than the two-way travel time. Presumably this is to allow the echo to be processed before the next click is produced. However, some species, such as the beluga (Delphinapterus leucas ), can produce clicks with intervals shorter than the two-way travel time ( Turl and Penner, 1989 ). When a dol-phin approaches an object, it decreases the outgoing level of its clicks to maintain the returning echoes at a near constant sound level ( Au and Benoit-Bird, 2003 ) and increases the rate of click production as the two-way travel time decreases.

Click structure varies between phylogenetic groups. Clicks pro-duced by sperm whales, beaked whales, dolphins, and porpoises can be differentiated by duration, waveform type, and frequency emphasis ( Tyack et al., 2006 ). Sperm whale clicks typically range from 400 Hz to at least 15 kHz ( Goold and Jones, 1995 ). The clicks of Blainville’s (Mesoplodon densirostris ) and Cuvier’s ( Ziphius cavirostris ) beaked whales have most of their energy in the 20–50 kHz region ( Johnson

et al., 2004 ). Delphinid clicks generally range from 60–120 kHz. Porpoise clicks are narrowband and usually well above 120 kHz.

Sperm whales are the largest toothed mammals on earth and have a disproportionately huge head. It is likely that the evolution of their huge head has, in large part, been driven by the loud and complicated structure of their relatively low-frequency clicks that are used for communication and echolocation.

Sperm whales produce a variety of clicks in a variety of contexts. Clicks can occur singly at different intervals, in a short pattern of dis-tinct clicks called “ codas, ” or in a long sequence of tightly spaced clicks known as “ creaks. ” The frequency content of clicks differs between sexes. It is known that large males have lower frequency content in their clicks than females and young males ( Goold and Jones, 1995 ).

“ Usual ” clicks are produced in a regular sequence at intervals of 1.17–1.95 sec with a duration between 2 and 24 msec ( Goold and Jones, 1995 ). The click interval varies greatly between individuals ( Goold and Jones, 1995 ), but appears to be stable within the click trains of an individual whale ( Fig. 8 ).

The stereotyped, repetitive patterns of clicks or codas are pro-duced primarily, if not only, by female sperm whales ( Marcoux et al.,2006 ) . While it had been suggested that codas serve the function of individual identifi cation, it is now known that coda repertoires are shared between individuals within a group ( Rendell and Whitehead, 2004 ). This suggests that codas are used in social communication, and perhaps group identity ( Weilgart and Whitehead, 1997 ). In

0.000kHz 1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 90s

Figure 8 The spectrogram and waveform of “ usual ” sperm whale ( Physeter macrocephalus ) clicks.

addition, individual social groups of sperm whales appear to belong to clans that share similar coda repertoires. These repertoires may be created and evolve through cultural transmission ( Rendell and Whitehead, 2003 ). This is supported by the fi nding that the degree of similarity of coda structure is inversely related to the distance between the groups. ( Rendell and Whitehead, 2005 ).

“ Creaks ” are a rapid sequence of clicks sounding more like a continuous buzzing sound than individual clicks. They occur when a sperm whale is approaching a potential prey item much like a dol-phin’s terminal buzz ( Miller et al., 2004 ; Watwood et al., 2006 ).

Sperm whale ‘ trumpet sounds ’ are usually produced at the start of a dive in some but not all populations. These sounds are a series of repeated calls, each about 0.2 sec long that occur in sequences lasting between 0.6 and 3.5 sec. Each of these calls is composed of an AM tonal waveform with a complex harmonic structure. The spectrum contains a low frequency component at 500 Hz and a mid-frequency component at 3 kHz ( Teloni et al., 2005 ).

Mature sperm whale males produce another type of click, called a “ slow click ” for its low repetition rate. These clicks are of longer dura-tion, with a mean of 72 msec compared to 24 msec for usual clicks. Slow clicks have consistent energy concentrations at 1.8 and 2.8 kHz, whereas the energy distribution in the spectra of usual clicks is much more variable. It has been suggested that slow clicks may serve as a long-range social communication signal ( Madsen et al., 2002 ).

Dolphins , with the exception of those in the genus Cephalorhynchus , produce short clicks lasting only a few cycles. The short duration necessarily produces a broadband signal with most of the energy typically found between 40 and 300 kHz across most species ( Au, 1993 ). The spectrum of white-beaked dolphin ( Lagenorhynchus albi-rostris ) clicks can span this entire range ( Rasmussen and Miller, 2002 ) while other species may have much narrower bandwidths. The clicks of many species contain two frequency peaks ( Au and Würsig, 2004 ). This may be the result of size differences in the two MLDB sound-generat-ing structures in the dolphin’s head ( Cranford, 2000 ). Click source levels can range between 150 and 230 dB re 1 μ Pa at 1 m (peak to peak).

Dolphins are able to alter the spectral characteristics and source level of their clicks. For example, when a captive beluga was moved from San Diego Bay to Kaneohe, Hawaii, it increased the frequency of its clicks from 40–60 to 100–120 kHz ( Au et al., 1985 ). Furthermore it has been shown that dolphins alter the source level of their clicks while echolocating. They click loudly when far away from the target and more softly as they approach the target. This is apparently done to decrease variation in the level of the returning echo ( Au and Benoit-Bird, 2003 ). Finally, there appears to be a relationship between the source level and the dominant frequency of the click, with louder clicks generally having higher frequency peaks ( Au and Würsig, 2004 ).

Porpoises, the genus Cephalorhynchus , the pygmy sperm whale (Kogia breviceps ) and franciscana ( Pontoporia blainvillei ) produce a very different type of click than the short broadband clicks described above. Called a narrowband high frequency (NBHF) click, they have relatively low power, a narrow bandwidth and a high center fre-quency ( Morisaka and Connor, 2007 ). NBHF clicks are longer (tens of cycles) than typical delphinid clicks, and have a smooth amplitude envelope ( Au, 1993 ). It may be that the evolution of these higher frequency NBHF clicks was an anti-predation response to killer whales ( Orcinus orca ), who may be unable to hear them ( Morisakaand Connor, 2007 ).

Beaked whales have recently been tagged with acoustic record-ers. Data from these recordings have provided both a description of beaked whale clicks and evidence that they are used for echoloca-tion ( Johnson et al., 2004 ). The measured source level of the clicks

is as high as 214 dB re 1 μ Pa at 1 m (peak to peak). The clicks of Blainville’s and Cuvier’s beaked whales typically show an upward frequency modulation and have very little energy below 20 kHz ( Johnson et al., 2004 ). A similar lack of low-frequency energy has been reported for the clicks of other beaked whale species ( Dawson et al., 1998 ).

2. Pulsed Sounds Pulsed sounds are a series of sound pulses with short intervals. The pulses can occur so quickly, one after the other, that they may be perceived as continuous sound ( Watkins, 1967 ). Short, discrete bursts of broadband sound pulses are referred to as burst-pulses. Typically, most of the energy is in the lower fre-quencies. However, the burst-pulses of some species can lack the low frequency components and extend up to 60 kHz or higher ( Lammerset al., 2003 ).

Burst-pulses appear to be used for communication between members of the group. Hawaiian spinner dolphins ( Stenella longi-rostris ) were closer together when they produced burst-pulses than when they used whistles, suggesting a differential function between these two signals ( Lammers et al., 2006 ). Stereotyped patterns of burst-pulse sounds have been described in right whale dolphins (Lissodelphis borealis ), suggesting that these sounds may have a communicative function similar to stereotyped whistles in other dol-phins ( Rankin et al., 2007 ).

In addition to their well-known click sounds, sperm whales produce rapidly pulsed sounds (up to � 1600 pulses/sec) that are described as “ squeals ” ( Weir et al., 2007 ). These squeals are lower in frequency than their clicks, with most energy below 2 kHz and last-ing about 1 sec.

Killer whales produce a large number of pulsed signals. The high repetition rate of up to 4000 pulses/sec lends a tonal charac-ter to their sounds. Most of the energy in these well-studied signals occurs between 1 and 6 kHz ( Ford, 1989 ). Resident killer whales in the Northeast Pacifi c share stereotyped pulsed calls or dialects within their stable social pods. Each pod has evolved its own dia-lect but may share calls with other pods. Pods with similar dialects that share calls are grouped together in acoustic clans ( Ford, 1991 ).Resident pods from different acoustic clans are known to associate, but not to share call types.

Dialects may have evolved through behavioral drift as ancestral groups divided into newer subgroups. The different dialects serve important social functions for group cohesion and inter-group rec-ognition ( Ford, 1991 ). Resident killer whales in Norway may have a similar dialect system ( Strager, 1995 ).

Transient killer whales of the Pacifi c Northwest (of the United States, and of southern Canada), that feed on marine mammals instead of fi sh, have dramatically different vocal behavior. They remain silent most of the time, emitting calls for specifi c functions such as locating other transient killer whales ( Saulitis et al., 2005 ). They also echolo-cate much less often than resident killer whales ( Barrett-Lennard et al., 1996 ). It is likely that this reduction in acoustic behavior evolved in response to the hearing abilities of their marine mammal prey.

3. Whistles Whistles are narrowband FM signals with a wide variety of contours ( i.e. frequency-modulation pattern) ranging from short and simple chirps to long complex signals. The frequency range of the fundamental frequency of whistles is typically between 1 and 30 kHz. Whistles can be as short as tens of milliseconds, most often between 500 and 1000 msec, and as long as 3 sec or more. Most dolphin species produce whistles, although some, like those in the genus Cephalorhynchus , do not ( Morisaka and Connor, 2007 ). All of the whistles of delphinid species share many characteristics and it

can be diffi cult to discriminate between them ( Oswald et al., 2007 ). However, additional recordings and analyses are helping to improve the identifi cation process.

There are no universally accepted classifi cations for whistles, although measures of beginning, ending, minimum and maximum frequency, and kind of frequency modulation are usually described. Whistles in some species can be readily grouped into categories while others form a continuum of structure. In bottlenose dolphins (Tursiops spp.), researchers tend to come up with tens of distinct whistle sounds, with many intergrading variations among them ( Deecke and Janik, 2006 ).

4. Signature Whistles Bottlenose dolphins, and probably quite a few other species as well, produce individualized whistle contours called signature whistles. These have been shown to function in maintaining group cohesion ( Janik and Slater, 1998 ) and to convey individual identity information that may be analogous to a “ name. ”This individual identity is encoded in the frequency contour of the whistle and not in the individual characteristics of the vocalization (i.e., the “ voice ” ) ( Janik et al., 2006 ). Bottlenose dolphins are the only nonhuman animals yet shown to have this capability. Dolphins are also able to mimic the signature whistles of other individuals in their group, an ability that appears to help maintain social bonds.

The formation of signature whistles is a learned behavior. Dolphin calves learn their signature whistles within their fi rst few months and retain them their entire lives. Interestingly, signature whistles in Florida bottlenose dolphins appear to be more alike in mothers and their male offspring than in mothers and their daughters ( Sayighet al., 1995 ). The Sarasota, Florida, population of dolphins is gen-erally matriarchal, with daughters being closely affi liated for many years or for life. However, sons leave the natal group as subadults. It has been hypothesized that sons and mothers thereby recognize each other easily after prolonged times apart, perhaps even for years. This recognition may help avoid inbreeding and facilitate other kin-related social behaviors, such as lowered aggression. Further research has shown that the Sarasota calves are more likely to model their signature whistles on those of other Sarasota dolphins, but ones with whom they rarely associate ( Fripp et al., 2005 ).

Debate continues over which dolphin species have signature whistles. It has been suggested that Pacifi c humpback dolphins (Sousa spp.) ( Van Parijs and Corkeron, 2001 ) and Atlantic spotted dolphins ( Stenella frontalis ) ( Herzing, 1996 ) produce them and it is likely that additional species possess them as well.

The complexity of whistle production may well relate to the complexity of behavior or “ excitement ” level. For example, resting long-fi nned pilot whales ( Globicephala melas ) make very simple non-wavering whistles. Whistle complexity increases during feed-ing and bouts of socializing, and variability of whistles and other sounds increases greatly when two pilot whale groups approach each other ( Weilgart and Whitehead, 1990 ). There is a general relation-ship between the activity level of Hawaiian spinner dolphin groups and their vocalization rate. A resting group produces few sounds, whereas a feeding or socially active group produces many sounds. Higher vocalization rates may result from increased vocalization by all members or from only a subset of individuals within the group. Vocalization behavior may also be related to differences in age, social status, alertness, and gender ( Norris et al., 1994 ).

D. Sounds of Sirenians and Other Groups Manatees are rather quiet but do produce sounds between 0.15

and 1 sec in duration. Signal structure can be complex, and frequencies

range between 600 Hz and 12 kHz, with most energy found between 2.5 and 5 kHz. The fundamental frequency is at times less intense than the fi rst harmonic. The source level has been estimated at 112 dB re 1 μ Pa at 1 m ( Phillips et al., 2004 ). Calls consist mainly of “ chirp-squeaks, ” “ squeals, ” and “ screams. ” Their calls contain per-sistent inter-individual differences, particularly in fundamental fre-quency, which is inversely correlated with body size ( O’Shea and Poche, 2006 ). Mothers and calves counter-call while rejoining each other, suggesting that they recognize individual call characteristics ( O’Shea and Poche, 2006 ).

Dugongs appear to vocalize more often than the manatees, producing three major sound types: chirp-squeaks, barks, and trills ( Anderson and Barclay, 1995 ). They also make intermediate sounds that include components of the three main types. Chirp-squeaks are short FM signals extending upward to 18 kHz. They are about 60 sec in duration, typically trend slightly downward in frequency, and have two to fi ve harmonics. Barks are loud broadband signals that range between 500 Hz and 2.2 kHz, lasting between 0.03 and 0.12 sec. Trills are a series of individual notes, lasting between 100 and 2200 msec. Notes typically begin at about 3.1 kHz and rise to 3.9 kHz. Instead of a linear sweep, the frequency contour has an oscillating charac-ter. While the functions of these sounds are uncertain, it is likely that they are used for social communication.

Sea otters ( Enhydra lutris ) produce at least 11 different airborne sounds: screams, baby cries, whistles, whines, hisses, snarls, coos, grunts, squeals, squeaks, and whimpers ( McShane et al., 1995 ). These vocalizations are short, lasting less than a second, and extremely vari-able in frequency and structure. Airborne vocalizations serve to main-tain the mother–pup bond. For example, a pup at the surface often vocalizes continuously until the mother resurfaces following a dive. However, if the mother surfaces and does not fi nd the pup, she vocal-izes and awaits the pup’s response ( Sandegren et al., 1973 ). Pups also vocalize to elicit nursing or grooming. No underwater vocalizations have been recorded.

Polar bears may not be quite as vocal as many other carnivores. Males chuff and snort with powerful rapid exhalations, especially in competitive interactions with other males. Females produce low mew-like calls that may be used for mother/pup recognition. Other calls include roars, growls, and bellows ( Brown, 1993 ).

IV. Conclusions Marine mammals have a very rich behavioral tapestry of sounds.

The basic description here merely hints at this richness in an envi-ronment where sight and smell are not transmitted as effi ciently as sound. Sound is used for communication and for wresting informa-tion from the environment. While only toothed whales are thought to have sophisticated echolocation, it is likely that many sounds give information on depth of water, obstruction ahead, or even silent con-specifi cs, simply by the alteration of sound refl ections in different environments.

Our acceptance that sound is critically important to marine mam-mals also gives us cause for concern. Since the advent of motorized shipping and more recently industrial seismic, military sonar and other human sources of sound, ambient noise levels in major parts of the oceans are increasing. We do not yet know the details of how this noise may affect the communication and behavior of marine mammals.

See Also the Following Articles

Communication ■ Echolocation ■ Intelligence and Cognition ■

Mimicry ■ Noise ■ Effects of ■ Signature Whistles ■ Song

References Anderson , P. K. , and Barclay , R. M. R. ( 1995 ). Acoustic signals of soli-

tary dugongs: physical characteristics and behavioral correlates .J. Mammal. 76 , 1226 – 1237 .

Asselin , S. , Hammill Mike , O. , and Barrette , C. ( 1993 ). Underwater vocalizations of ice breeding grey seals . Can. J. Zool. 71 , 2211 – 2219 .

Au , W. , Carder , D. , Penner , R. H. , and Scronce , B. L. ( 1985 ). Demonstration of adaptation in beluga whale echolocation signals . J. Acoust. Soc. Am. 77 , 726 – 730 .

Au , W. W. L. ( 1993 ). “ The Sonar of Dolphins . ” Springer-Verlag , New York .

Au , W. W. L. , and Benoit-Bird , K. J. ( 2003 ). Automatic gain control in the echolocation system of dolphins . Nature 423 , 861 – 863 .

Au , W. W. L. , and Würsig , B. ( 2004 ). Echolocation signals of dusky dolphins ( Lagenorhynchus obscurus ) in Kaikoura, New Zealand .J. Acoust. Soc. Am. 115 , 2307 – 2313 .

Ballard , K. A. , and Kovacs , K. M. ( 1995 ). The acoustic repertoire of hooded seals ( Cystophora cristata ) . Can. J. Zool. 73 , 1362 – 1374 .

Barrett-Lennard , L. G. , Ford , J. K. B. , and Heise , K. A. ( 1996 ). The mixed blessing of echolocation: differences in sonar use by fi sh-eating and mammal-eating killer whales . Anim. Behav. 51 , 553 – 565 .

Bartholomew , G. A. , and Collias , N. E. ( 1962 ). The role of vocalization in the social behaviour of the northern elephant seal . Anim. Behav. 10 , 7 – 14 .

Beier , J. C. , and Wartzok , D. ( 1979 ). Mating behavior of captive spotted seals ( Phoca largha ) . Anim. Behav. 27 , 772 – 781 .

Brown , G. ( 1993 ). “ The Great Bear Almanac . ” Lyons and Burford , New York .

Cerchio , S. , and Dalheim , M. ( 2001 ). Variations in feeding vocaliza-tions of humpback whales ( Megaptera novaeangliae ) from Southeast Alaska . Bioacoustics 11 , 277 – 295 .

Charif , R. A. , Mellinger , D. K. , Dunsmore , K. J. , and Clark , C. W. ( 2002 ). Estimated source levels of fi n whale (Balaenoptera physalus)vocalizations: Adjustments for surface interference . Mar. Mamm. Sci. 18 , 81 – 98 .

Charrier , I. , and Harcourt , R. G. ( 2006 ). Individual vocal identity in mother and pup Australian sea lions ( Neophoca cinerea ) . J. Mammal. 87 , 929 – 938 .

Clark , C. W. ( 1983 ). Acoustic communication and behavior of the southern right whale ( Eubalaena australis) . In “ Communication and Behavior of Whales ” ( R. Payne , ed. ) , pp. 163 – 198 . Westview Press , Boulder .

Clark , C. W. , and Clapham , P. J. ( 2004 ). Acoustic monitoring on a hump-back whale ( Megaptera novaeangliae ) feeding ground shows contin-ual singing into late spring . Proc. R. Soc. Lond., B. 271 , 1051 – 1057 .

Cranford , T. ( 2000 ). In search of impulse sound sources in odontocetes .In “ Hearing by Whales and Dolphins ” ( W. W. L. Au , A. N. Popper , and R. R. Fay , eds ) , pp. 109 – 155 . Springer-Verlag , New York .

Cranford , T. W. ( 1999 ). The sperm whale’s nose: sexual selection on a grand scale? Mar. Mamm. Sci. 15 , 1133 – 1157 .

Croll , D. A. , Clark , C. W. , Acevedo , A. , Tershy , B. , Floress , S. , Gedamke , J. , and Urban , J. ( 2002 ). Only Male Fin Whales Sing Loud Songs .Nature 417 , 809 .

Cummings , W. C. , Thompson , P. O. , and Ha , S. J. ( 1986 ). Sounds from Bryde, Balaenoptera edeni , and fi nback, B. physalus , whales in the Gulf of California . Fish Bull. 84 , 359 – 370 .

Dahlheim , M. E. , Fisher , H. D. , and Schempp , J. D. ( 1984 ). Sound production by the gray whale and ambient noise levels in Laguna San Ignacio, Baja California Sur, Mexico . In “ The Gray Whale ( Eschrichtius robustus ) ” ( M. L. Jones , S. L. Swartz , and S. Leatherwood , eds ) , pp. 511 – 541 . Academic Press, Inc. , London .

Dawbin , W. H. , and Cato , D. H. ( 1992 ). Sounds of a pygmy right whale Caperea marginata . Mar. Mamm. Sci. 8 , 213 – 219 .

Dawson , S. , Barlow , J. , and Ljungblad , D. ( 1998 ). Sounds recorded from Baird’s beaked whale, Berardius bairdii . Mar. Mamm. Sci. 14 , 335 – 344 .

Deecke , V. B. , and Janik , V. M. ( 2006 ). Automated categorization of bio-acoustic signals: avoiding perceptual pitfalls . J. Acoust. Soc. Am. 119 , 645 – 653 .

Edds , P. L. , Odell , D. K. , and Tershy , B. R. ( 1993 ). Vocalizations of a captive juvenile and free-ranging adult-calf pairs of Bryde’s whales, Balaenoptera edeni . Mar. Mamm. Sci. 9 , 269 – 284 .

Eriksen , N. , Miller , L. A. , Tougaard , J. , and Helweg , D. A. ( 2005 ). Cultural change in the songs of humpback whales ( Megaptera novae-angliae ) from Tonga . Behaviour 142 , 305 – 328 .

Esch, H. C., Baumgartner, M. F., Wenzel, F., and Van Parijs, S. (2007). Automated detection of stereotyped baleen whale vocalizations: Advantages over traditional methods. 17th Biennial Conference on the Biology of Marine Mammals. Capetown, South Africa .

Fernández-Juricic , E. , Campagna , C. , Enriquez , V. , and Ortiz , C. L. ( 1999 ). Vocal communication and individual variation in breeding South American sea lions . Behaviour 136 , 495 – 517 .

Fitch , W. T. , Neubauer , J. , and Herzel , H. ( 2002 ). Calls out of chaos: the adaptive signifi cance of nonlinear phenomena in mammalian vocal production . Anim. Behav. 63 , 407 – 418 .

Ford , J. K. B. ( 1989 ). Acoustic behaviour of resident killer whales ( Orcinus orca ) off Vancouver Island, British Columbia . Can. J. Zool. 67 , 727 – 745 .

Ford , J. K. B. ( 1991 ). Vocal traditions among resident killer whales (Orcinus orca ) in coastal waters of British Columbia . Can. J. Zool. 69 , 1454 – 1483 .

Frankel , A. S. , Clark , C. W. , Herman , L. M. , and Gabriele , C. M. ( 1995 ). Spatial distribution, habitat utilization, and social interactions of humpback whales, Megaptera novaeangliae , off Hawaii, determined using Acoustic and Visual Techniques . Can. J. Zool. 73 , 1134 – 1146 .

Fripp , D. ( 2005 ). Bubblestream whistles are not representative of a bot-tlenose dolphin’s vocal repertoire . Mar. Mamm. Sci. 21 , 29 – 44 .

Fripp , D. , Owen , C. , Quintana-Rizzo , E. , Shapiro , A. , Buckstaff , K. , Jankowski , K. , Wells , R. , et al . ( 2005 ). Bottlenose dolphin ( Tursiops truncatus ) calves appear to model their signature whistles on the sig-nature whistles of community members . Anim. Cogn. 8 , 17 – 26 .

Gabriele , C. M. , and Frankel , A. S. ( 2002 ). The occurrence and signifi -cance of humpback whale songs in Glacier Bay, Southeastern Alaska .Arct. Res. U.S.A. 16 , 42 – 47 .

Gedamke , J. , Costa , D. P. , and Dunstan , A. ( 2001 ). Localization and vis-ual verifi cation of a complex minke whale vocalization . J. Acoust. Soc. Am. 109 , 3038 – 3047 .

George , J. C. , Clark , C. , Carroll , G. M. , and Ellison , W. T. ( 1989 ). Observations on the ice-breaking and ice navigation behavior of migrating bowhead whales ( Balaena mysticetus ) near Point Barrow, Alaska, Spring 1985 . Arctic. 42 , 24 – 30 .

Goold , J. C. , and Jones , S. E. ( 1995 ). Time and frequency domain char-acteristics of sperm whale clicks . J. Acoust. Soc. Am. 98 , 1279 – 1291 .

Hanggi , E. B. , and Schusterman , R. J. ( 1994 ). Underwater acoustic dis-plays and individual variation in male harbour seals Phoca vitulina . Anim. Behav. 48 , 1275 – 1283 .

Hartmann , W. H. ( 2004 ). “ Signals, Sound, and Sensation . ” American Institute of Physics . Springer-Verlag, New York.

Hayes , S. A. , Kumar , A. , Costa , D. P. , Mellinger , D. K. , Harvey , J. T. , Southall , B. L. , and Le Boeuf , B. J. ( 2004 ). Evaluating the function of the male harbour seal, Phoca vitulina , roar through playback experi-ments . Anim. Behav. 67 , 1133 – 1139 .

Herzing , D. L. ( 1996 ). Vocalizations and associated underwater behavior of free-ranging Atlantic spotted dolphins, Stenella frontalis and bot-tlenose dolphins, Tursiops truncatus . Aq. Mamm. 22 , 61 – 79 .

Janik , V. M. , Sayigh , L. S. , and Wells , R. S. ( 2006 ). Signature whistle shape conveys identity information to bottlenose dolphins . Proc. Natl. Acad. Sci. U.S.A. 103 , 8293 – 8297 .

Janik , V. M. , and Slater , P. J. B. ( 1998 ). Context-specifi c use suggests that bottlenose dolphin signature whistles are cohesion calls . Anim.Behav. 56 , 829 – 838 .

Johnson , M. , Madsen , P. T. , Zimmer , W. M. X. , Aguilar de Soto , N. , and Tyack , P. L. ( 2004 ). Beaked whales echolocate on prey . Proc. R. Soc. Lond., B. Biol. Sci. 271 , S383 – S386 .

Knowlton, A., Clark, C. W., and Kraus, S. D. (1991). Sounds recorded in the presence of sei whales, Balaenoptera borealis . Ninth biennial conference on the biology of marine mammals, Chicago.

Kunnasranta , M. , Heikki , H. , and Sorjonen , J. ( 1996 ). Underwater vocal-izations of Ladoga ringed seals ( Phoca hispida ladogensis Nordq.) in summertime . Mar. Mamm. Sci. 12 , 611 – 618 .

Lammers , M. O. , Au , W. W. L. , and Herzing , D. L. ( 2003 ). The broad-band social acoustic signaling behavior of spinner and spotted dol-phins . J. Acoust. Soc. Am. 114 , 1629 – 1639 .

Lammers, M. O., Schotten, M., and Au, W. W. L. (2006). The spatial context of free-ranging Hawaiian spinner dolphins ( Stenella longiros-tris ) producing acoustic signals. J. Acoust. Soc. Am. 119, 1244–1250.

Madsen , P. T. , Wahlberg , M. , and Mohl , B. ( 2002 ). Male sperm whale (Physeter macrocephalus ) acoustics in a high- latitude habitat: impli-cations for echolocation and communication . Behav. Ecol. Sociobiol. 53 , 31 – 41 .

Marcoux , M. , Whitehead , H. , and Rendell , L. ( 2006 ). Coda vocalizations recorded in breeding areas are almost entirely produced by mature female sperm whales ( Physeter macrocephalus ) . Can. J. Zool. 84 , 609 – 614 .

McDonald , M. A. ( 2006 ). An acoustic survey of baleen whales off Great Barrier Island, New Zealand . N. Z. J. Mar. Freshwater Res. 40 , 519 – 529 .

McDonald , M. A. , Calambokidis , J. , Teranishi , A. M. , and Hildebrand , J. A. ( 2001 ). The acoustic calls of blue whales off California with gender data . J. Acoust. Soc. Am. 109 , 1728 – 1735 .

McDonald , M. A. , Hildebrand , J. A. , Wiggins , S. M. , Thiele , D. , Glasgow , D. , and Moore , S. E. ( 2005 ). Sei whale sounds recorded in the Antarctic . J. Acoust. Soc. Am. 118 , 3941 – 3945 .

McDonald , M. A. , Mesnick , S. L. , and Hildebrand , J. A. ( 2006 ). Biogeographic characterisation of blue whale song worldwide: using song to identify populations . J. Cetacean Res. Manage. 8 , 55 – 65 .

McShane , L. J. , Estes , J. A. , Riedman , M. L. , and Staedler , M. M. ( 1995 ). Repertoire, structure, and individual variation of vocalizations in the sea otter . J. Mammal. 76 , 414 – 427 .

Merlen , G. ( 2000 ). Nocturnal acoustic location of the Galapagos Fur Seal Arctocephalus galapagoensis . Mar. Mamm. Sci. 16 , 248 – 253 .

Miller , E. H. ( 1985 ). Airborne acoustic communication in the Walrus (Odobenus rosmarus ) . Nat. Geogr. Res. 1, 124 – 145 .

Miller , E. H. , and Job , D. A. ( 1992 ). Airborne acoustic communication in the Hawaiian monk seal, Monachus schauinslandi . In “ Marine Mammal Sensory Systems ” ( J. A. Thomas , R. A. Kastelein , and A. Y. Supin , eds ) , pp. 485 – 531 . Plenum , New York .

Miller , P. J. O. , Johnson , M. P. , and Tyack , P. L. ( 2004 ). Sperm whale behaviour indicates the use of echolocation click buzzes “ creaks ” in prey capture . Proc. R. Soc. Lond., B. Biol. Sci. 271 , 2239 – 2247 .

Moore , S. E. , and Ljungblad , D. K. ( 1984 ). Gray whales in the Beaufort, Chukchi and Bering seas: distribution and sound production . In “ The Gray Whale ” ( M. L. Jones , S. L. Swartz , and S. Leatherwood , eds ) , pp. 543 – 559 . Academic Press , New York .

Moore , S. E. , Stafford , K. M. , Dahlheim , M. E. , Fox , C. G. , Braham , H. W. , Polovin , J. J. , and Bain , D. E. ( 1998 ). Seasonal variation in reception of fi n whale calls at fi ve geographic areas in the North Pacifi c . Mar. Mamm. Sci. 14 , 617 – 627 .

Morisaka , T. , and Connor , R. C. ( 2007 ). Predation by killer whales (Orcinus orca ) and the evolution of whistle loss and narrow-band high frequency clicks in odontocetes . J. Evol. Biol. 20 , 1439 – 1458 .

Norris , K. S. ( 1968 ). The evolution of acoustic mechanisms in odon-tocete cetaceans . In “ Evolution and environment ” ( E. T. Drake , ed. ) , pp. 297 – 324 . Yale University Press , New Haven .

Norris , K. S. , Würsig , B. , Wells , R. S. , and Würsig , M. ( 1994 ). “ The Hawaiian spinner dolphin . ” University of California Press , Berkeley .

O’Shea , T. , and Poche , L. B. , Jr. ( 2006 ). Aspects of underwater sound communication in Florida manatees ( Trichechus manatus latirostris ) . J. Mammal. 87 , 1061 – 1071 .

Oetelaar , M. L. , Terhune , J. M. , and Burton , H. R. ( 2003 ). Can the sex of a Weddell seal ( Leptonychotes weddellii ) be identifi ed by its surface call? Aq. Mamm. 29 , 261 – 267 .

Oleson , E. M. , Barlow , J. , Gordon , J. , Rankin , S. , and Hildebrand , J. A. ( 2003 ). Low frequency calls of Bryde’s whales . Mar. Mamm. Sci. 19 , 407 – 419 .

Oleson , E. M. , Calambokidis , J. , Burgess , W. C. , McDonald , M. A. , LeDuc , C. A. , and Hildebrand , J. A. ( 2007 ). Behavioral context of call production by eastern North Pacifi c blue whales . Mar. Ecol. Prog. Ser. 330 , 269 – 284 .

Oswald , J. N. , Rankin , S. , Barlow , J. , and Lammers , M. O. ( 2007 ). A tool for real-time acoustic species identifi cation of delphinid whistles . J. Acoust. Soc. Am. 122 , 587 – 595 .

Outi, T., Parks, S., and Miller, L. A. (2007). Annual and seasonal changes in the song of the bowhead whales Balaena mysticetus in Disko Bay, Western Greenland. 17th Biennial Conference on the Biology of Marine Mammals. Capetown, South Africa .

Page , B. , Goldsworthy , S. D. , Hindell , M. A. , and McKenzie , J. ( 2002 ). Interspecifi c differences in male vocalizations of three sympatric fur seals ( Arctocephalus spp.) . J. Zool. Lond. 258 , 49 – 56 .

Parks , S. E. , Hamilton , P. K. , Kraus , S. D. , and Tyack , P. L. ( 2005 ). The gunshot sound produced by male North Atlantic right whales (Eubalaena glacialis ) and its potential function in reproductive adver-tisement . Mar. Mamm. Sci. 21 , 458 – 475 .

Payne , K. , and Payne , R. ( 1985 ). Large scale changes over 19 years in songs of humpback whales in Bermuda . Z. Tierpsychol. 68 , 89 – 114 .

Payne , K. , Tyack , P. , and Payne , R. ( 1983 ). Progressive changes in the songs of humpback whales ( Megaptera novaeangliae ): a detailed analysis of two seasons in Hawaii . In “ Communication and Behavior of Whales ” ( R. Payne , ed. ) , pp. 9 – 57 . Westview Press , Boulder .

Payne , R. , and Guinee , L. N. ( 1983 ). Humpback whale ( Megapteranovaeangliae ) songs as an indicator of “ stocks ” . In “ Communication and Behavior of Whales ” ( R. Payne , ed. ) , pp. 333 – 368 . Westview Press , Boulder .

Payne , R. , and Webb , D. ( 1971 ). Orientation by means of long range acoustic signaling in baleen whales . Ann. N. Y. Acad. Sci. 188 , 110 – 142 .

Petrochenko , S. P. , Potapov , A. S. , and Pryadko , V. V. ( 1991 ). Sounds, source levels, and behavior of gray whales in the Chukotsoe Sea . Sov. Phys. Acoust. 37 , 622 – 624 .

Phillips , A. V. , and Stirling , I. ( 2001 ). Vocal repertoire of South American fur seals, Arctocephalus australis : structure, function, and context .Can. J. Zool. 79 , 420 – 437 .

Phillips , R. , Niezrecki , C. , and Beusse , D. O. ( 2004 ). Determination of West Indian manatee vocalization levels and rate . J. Acoust. Soc. Am. 115 , 422 – 428 .

Poulter , T. C. ( 1968 ). Underwater vocalization and behavior of pinni-peds . In “ The Behavior and Physiology of Pinnipeds ” ( R. J. Harrison , R. C. Hubbard , R. S. Peterson , C. E. Rice , and R. J. Schusterman , eds ) , pp. 69 – 84 . Appleton-Century-Crofts , New York .

Rankin , S. , and Barlow , J. ( 2005 ). Source of the North Pacifi c “ boing ” sound attributed to minke whales . J. Acoust. Soc. Am. 118 , 3346 – 3351 .

Rankin , S. , Oswald , J. , Barlow , J. , and Lammers , M. ( 2007 ). Patternedburst-pulse vocalizations of the northern right whale dolphin, Lissodelphis borealis . J. Acoust. Soc. Am. 121 , 1213 – 1218 .

Rasmussen , M. H. , and Miller , L. A. ( 2002 ). Whistles and clicks from white-beaked dolphins, Lagenorhynchus albirostris , recorded in Faxafl oi Bay, Iceland . Aq. Mamm. 28 , 78 – 89 .

Reidenberg , J. S. , and Laitman , J. T. ( 2007 ). Discovery of a low fre-quency sound source in Mysticeti (baleen whales): anatomical estab-lishment of a vocal fold homolog . Anat. Rec. 290 , 745 – 759 .

Rendell , L. , and Whitehead , H. ( 2004 ). Do sperm whales share coda vocalizations?—Insights into coda usage from acoustic size measure-ment . Anim. Behav. 67 , 865 – 874 .

Rendell , L. , and Whitehead , H. ( 2005 ). Spatial and temporal variation in sperm whale coda vocalizations: stable usage and local dialects . Anim.Behav. 70 , 191 – 198 .

Rendell , L. E. , and Whitehead , H. ( 2003 ). Vocal clans in sperm whales (Physeter macrocephalus ) . Proc. R. Soc. Lond. B 270 , 225 – 231 .

Richardson , W. J. , Greene , C. R. , Malme , C. I. , and Thomson , D. H. ( 1995 ). “ Marine Mammals and Noise . ” Academic Press , San Diego .

Risch , D. , Clark , C. W. , Corkeron , P. J. , Elepfandt , A. , Kovacs , K. M. , Lydersen , C. , Stirling , I. , and Parijs , S. M. V. ( 2007 ). Vocalizations of male bearded seals, Erignathus barbatus : classifi cation and geograph-ical variation . Anim. Behav. 73 , 747 – 762 .

Rogers , T. L. , and Cato , D. H. ( 2002 ). Individual variation in the acous-tic behaviour of the adult male leopard seal, Hydrurga leptonyx . Behaviour 139 , 1267 – 1286 .

Rogers , T. L. , Cato Douglas , H. , and Bryden , M. M. ( 1996 ). Behavioral signifi cance of underwater vocalizations of captive leopard seals, Hydrurga leptonyx . Mar. Mamm. Sci. 12 , 414 – 427 .

Sandegren , F. ( 1976 ). Agonistic behavior in the male northern elephant seal . Behaviour 57 , 136 – 158 .

Sandegren , F. , Chu , E. , and Vandevere , J. ( 1973 ). Maternal behavior in the California sea otter . J. Mammal. 54 , 668 – 679 .

Sanvito , S. , Galimberti , F. , and Miller , E. H. ( 2007 ). Vocal signalling of male southern elephant seals is honest but imprecise . Anim. Behav. 73 , 287 – 299 .

Saulitis , E. L. , Matkin , C. O. , and Fay , F. H. ( 2005 ). Vocal repertoire and acoustic behavior of the isolated AT1 killer whale subpopulation in southern Alaska . Can. J. Zool. 83 , 1015 – 1029 .

Sayigh , L. S. , Tyack , P. L. , Wells , R. S. , Scott , M. D. , and Irvine , A. B. ( 1995 ). Sex difference in signature whistle production of free-ranging bottlenose dolphins, Tursiops truncatus . Behav. Ecol. Sociobiol. 36 , 171 – 177 .

Schusterman , R. J. , and Balliet , R. F. ( 1969 ). Underwater barking by male sea lions ( Zalophus californianus ) . Nature 222 , 1179 – 1181 .

Schusterman , R. J. , and Van Parijs , S. M. ( 2003 ). Pinniped vocal commu-nication: an introduction . Aq. Mamm. 29 , 177 – 180 .

Serrano , A. , and Terhune , J. M. ( 2002 ). Stability of the underwater vocal repertoire of harp seals ( Pagophilus groenlandicus ) . Aq. Mamm. 28 , 93 – 101 .

Sharpe, F. A. (2001). Social foraging of the Southeast Alaskan humpback whale. Ph.D. Dissertation, Simon Fraser University, Burnaby.

Shipley , C. , Hines , M. , and Buchwald , J. S. ( 1981 ). Individual differ-ences in threat calls of northern elephant seal bulls Anim . Behav. 29 , 12 – 19 .

Shipley , C. , Hines , M. , and Buchwald , J. S. ( 1986 ). Vocalizations of northern elephant seal bulls ( Mirounga angustirostris ): development of adult call characteristics during puberty . J. Mammal. 67 , 526 – 536 .

Shipley , C. , Stewart , B. S. , and Bass , J. ( 1992 ). Seismic communication in northern elephant seals . In “ Marine Mammal Sensory Systems ” ( J. A. Thomas , R. A. Kastelein , and A. Y. Supin , eds ) , pp. 553 – 562 . Plenum Press , New York .

Silber , G. K. ( 1986 ). The relationship of social vocalizations to surface behavior and aggression in the Hawaiian humpback whale Megapteranovaeangliae . Can. J. Zool. 64 , 2075 – 2080 .

Sjare , B. , Stirling , I. , and Spencer , C. ( 2003 ). Structural variation in the songs of Atlantic walruses breeding in the Canadian High Arctic . Aq.Mamm. 29 , 297 – 318 .

Stafford , K. M. , Moore , S. E. , and Fox , C. G. ( 2005 ). Diel variation in blue whale calls recorded in the eastern tropical Pacifi c . Anim. Behav. 69 , 951 – 958 .

Stimpert , A. K. , Wiley , D. N. , Au , W. W. L. , Johnson , M. P. , and Arsenault , R. ( 2007 ). Megapclicks ’ : acoustic click trains and buzzes produced during night-time foraging of humpback whales ( Megapteranovaeangliae ) . Biol. Lett. 3 , 467 – 470 .

Stirling , I. ( 1973 ). Vocalization in the ringed seal ( Phoca hispida ) . J. Fish. Res. Board Can. 30 , 1592 – 1593 .

Stirling , I. , Calvert , W. , and Cleator , H. ( 1983 ). Underwater vocalizations as a tool for studying the distribution and relative abundance of win-tering pinnipeds in the High Arctic . Arctic 36 , 262 – 274 .

Stirling , I. , and Siniff , D. B. ( 1979 ). Underwater vocalizations of leopard seals ( Hydurga leptonyx ) and crabeater seals ( Lobodon carcinopha-gus ) near the South Shetland Islands, Antarctica . Can. J. Zool. 57 , 1244 – 1248 .

Stirling , I. , and Thomas , J. A. ( 2003 ). Relationships between underwa-ter vocalizations and mating systems in phocid seals . Aq. Mamm. 29 , 227 – 246 .

Strager , H. ( 1995 ). Pod-specifi c call repertoires and compound calls of killer whales, Orcinus orca Linnaeus, 1758, in the waters of northern Norway . Can. J. Zool. 73 , 1037 – 1047 .

Teloni , V. , Zimmer , W. M. X. , and Tyack , P. L. ( 2005 ). Sperm whale trumpet sounds . Bioacoustics 15 , 163 – 174 .

Terhune , J. M. ( 1994 ). Geographical variation of harp seal underwater vocalizations . Can. J. Zool. 72 , 892 – 897 .

Terhune , J. M. , and Dell’Apa , A. ( 2006 ). Stereotyped calling patterns of a male Weddell seal ( Leptonychotes weddellii ) . Aq. Mamm. 32 , 175 – 181 .

Thomas , J. A. , and Golladay , C. L. ( 1995 ). Geographic variation in leop-ard seal ( Hydrurga leptonyx ) underwater vocalizations . In “ Sensory Systems of Aquatic Mammals ” ( R. A. Kastelein , ed. ) , pp. 201 – 222 . De Spil , Woerden .

Thompson , P. O. , Findley , L. T. , and Vidal , O. ( 1992 ). 20-Hz pulses and other vocalizations of fi n whales, Balaenoptera physalus , in the Gulf of California, Mexico . J. Acoust. Soc. Am. 92 , 3051 – 3057 .

Thompson, T. J., Winn, H. E., and Perkins, P. J. (1979). Mysticete Sounds. In “ Behavior of Marine Animals: Current Perspectives in Research ” (H. E. Winn and B. L. Olla, Eds.), 3: Cetaceans, pp. 403–431.

Tripovich , J. S. , Rogers , T. L. , and Arnould , J. P. Y. ( 2005 ). Species-specifi c characteristics and individual variation of the bark call pro-duced by male Australian fur seals ( Arctocephalus pusillus doriferus ) . Bioacoustics 15 , 79 – 96 .

Turl , C. W. , and Penner , R. H. ( 1989 ). Differences in echolocation click patterns of the beluga ( Delphinapterus leucas ) and the bottlenose dolphin ( Tursiops truncatus ) . J. Acoust. Soc. Am. 86 , 497 – 502 .

Tyack , P. , Johnson , M. , Zimmer , W. M. X. , Aguilar de Soto , N. , and Madsen , P. T. ( 2006 ). Acoustic behavior of beaked whales, with implications for acoustic monitoring . Oceans September , 1 – 6 , doi:10.1109/OCEANS.2006.307120 .

Tyack , P. , and Miller , E. H. ( 2002 ). Vocal anatomy, acoustic communica-tion and echolocation . In “ Marine Mammal Biology: An Evolutionary Approach ” ( A. R. Hoelzel , ed. ) , pp. 142 – 184 . Blackwell Publishing , Malden .

Urick , R. J. ( 1983 ). “ Principles of Underwater Sound . ” McGraw-Hill Book Company , New York .

Van Parijs , S. M. ( 2003 ). Aquatic mating in pinnipeds: a review . Aq.Mamm. 29 , 214 – 226 .

Van Parijs , S. M. , and Corkeron , P. J. ( 2001 ). Evidence for signature whistle production by a Pacifi c humpback dolphin, Sousa chinensis . Mar. Mamm. Sci. 17 , 944 – 949 .

Watkins , W. A. ( 1967 ). The harmonic interval fact or artifact in spectral analysis of pulse trains . In “ Marine Bio-Acoustics ” ( W. N. Tavolga , ed. ) , 2 , pp. 15 – 43 . Pergamon Press , New York .

Watkins , W. A. , and Ray , G. C. ( 1977 ). Underwater sounds from ribbon seal, Phoca fasciata . Fish Bull. 75 , 450 – 453 .

Watkins , W. A. , and Ray , G. C. ( 1985 ). In-air and underwater sounds of the Ross seal, ( Ommatophoca rossi ) . J. Acoust. Soc. Am. 77 , 1598 – 1600 .

Watkins , W. A. , and Schevill , W. E. ( 1976 ). Right whale feeding and baleen rattle . J. Mammal. 57 , 58 – 66 .

Watkins , W. A. , Tyack , P. , and Moore , K. E. ( 1987 ). The 20-Hz signals of fi nback whales ( Balaenoptera physalus ) . J. Acoust. Soc. Am. 82 , 1901 – 1912 .

Watwood , S. L. , Miller , P. J. O. , Johnson , M. , Madsen , P. T. , and Tyack , P. L. ( 2006 ). Deep-diving foraging behaviour of sperm whales ( Physetermacrocephalus ) . J. Anim. Ecol. 75 , 814 – 825 .

Weilgart , L. , and Whitehead , H. ( 1997 ). Group-specifi c dialects and geo-graphical variation in coda repertoire in South Pacifi c sperm whales .Behav. Ecol. Sociobiol. 40 , 277 – 285 .

Weilgart , L. S. , and Whitehead , H. ( 1990 ). Vocalizations of the North Atlantic pilot whale Globicephala melas as related to behavioral con-texts . Behav. Ecol. Sociobiol. 26 , 399 – 402 .

South American Aquatic Mammals 1071

Weir , C. R. , Frantzis , A. , Alexiadou , P. , and Goold , J. C. ( 2007 ). The burst-pulse nature of ‘ squeal ’ sounds emitted by sperm whales (Physeter macrocephalus ) . J. Mar. Biol. Assoc. U.K. 87 , 39 – 46 .

Wenz , G. M. ( 1964 ). Curious noises and the sonic environment in the ocean . In “ Marine Bio-acoustics ” ( W. N. Tavolga , ed. ) , pp. 101 – 119 . Pergamon Press , New York .

Winn , H. E. , and Perkins , P. J. ( 1976 ). Distribution and sounds of the minke whale, with a review of mysticete sounds . Cetology 19 , 1 – 12 .

Zoidis, A. M. et al. (8 authors) (2008). Vocalizations produced by humback whale (Megaptera novaeangliae) calves recorded in Hawaii. J. Acoust. Soc. Am . 123, 1737–1746.

South American Aquatic Mammals

ENRIQUE A. CRESPO

I. South American Marine and Fresh Water Ecosystems

The marine and fresh-water ecosystems of South America are very rich in aquatic mammals. Seventy-one species have been reported to occur within these ecosystems ( Table I ); most

breed locally, and only fi ve species that appear occasionally belong to Antarctic or subantarctic ecosystems ( Jefferson et al., 1993 ). A number of species are found in South America that occur in other parts of the world or the Southern Hemisphere, such as rorquals, ziphiids, and some delphinids. However, 20 species can be consid-ered endemic to the coastal waters or the river systems of South America.

The distribution of marine mammals at sea is related to the dis-tribution pattern of ocean currents that is defi ned by the characteris-tics of the major water masses, mainly temperature and salinity. The marine mammal assemblages of South America can be explained in part by the water masses that move around the continent ( Fig. 1 ). However, depth and ocean productivity may also play an important role in the presence, absence, or high concentration of individuals of a given species. Four different water masses each have their own wildlife marine mammal assemblage. These are Humboldt Current, Equatorial Front of the Eastern Tropical Pacifi c, Malvinas ( � Falkland)Current, and Brazil and South Equatorial Atlantic Currents. In addi-tion, a fi fth wildlife component is found in continental waters; it is heterogeneous due to the isolation between some of the river basins. Finally, a sixth assemblage that could be defi ned as “ erratic circumpo-lar ” can also be found. However, it is composed of isolated individu-als from Antarctic or sub-antarctic populations that breed or live southward of the Polar Front but move erratically in northern water masses.

II. Marine Mammals of Cold Water Marine Ecosystems

In the extreme south of the continent, the Antarctic Circumpolar Current moves from West to East and splits into two branches: the Malvinas Current in the Atlantic and the Humboldt Current in the Pacifi c. The cold marine ecosystem in the Pacifi c almost reaches

the equator with waters between 8 and 15°C, but in the Atlantic, the cold-temperate system reaches only to 40°S. Off Perú an upwelling system gives rise to high levels of primary and secondary productivity.

Several cold-water marine mammals are found in both the Humboldt and the Malvinas Currents ( Cárdenas et al., 1986 ). Among those species the most common in coastal waters are two ota-riids (the South American sea lion Otaria fl avescens and the South American fur seal Arctocephalus australis) and two small cetaceans (the dusky dolphin Lagenorhynchus obscurus and Burmeister’s por-poise Phocoena spinipinnis) . Other small cetaceans like the dolphins of the genus Lagenorhynchus ( L. australis and L. cruciger , the lat-ter more pelagic and less known) and the southern right whale dol-phin ( Lissodelphis peronii ) can be included. Two related species, the Chilean dolphin ( Cephalorhynchus eutropia ) in the Pacifi c and the Commerson’s dolphin ( C. commersonii ) in the Atlantic are endemic to the southern parts of the ecosystems.

One of the most conspicuous species in the southwestern Atlantic is the southern right whale ( Eubalaena australis ). With a geographic distribution between 20 and 55°S, one of the highest breeding con-centrations is at Península Valdés (42°S) ( Cappozzo et al., 1991 ). After long-term depletion of its population size; it is now recover-ing at rates over 7%, like other stocks in South Africa, Australia, and New Zealand. The whales can be observed in several places in the Atlantic: Uruguay, southern Brazil, and Buenos Aires Province in Argentina. At Santa Catarina, Brazil, a new breeding area was estab-lished and connected to Península Valdés. On the Pacifi c side, there are signs of recovery and a possible northward extension of the dis-tribution range. The stocks of Península Valdés and South Africa use the waters around South Georgia as a feeding ground.

The spectacled porpoise ( Phocoena dioptrica ) is known from the eastern coast of South America and several subantarctic islands, and the South American marine otter ( Lontra felina ) is known from Perú to Staten Island in the southern South Atlantic. Two fur seals (Arctocephalus galapagoensis and A. phillippi ) are endemic to the Galápagos and the Juan Fernández Archipelagos, respectively. The lat-ter is also found in a few other places in Perú and Chile. The Galápagos are also home to an endemic sea lion, Zalophus wollebaecki .

The long-fi nned pilot whale ( Globicephala melas ), Risso’s dolphin (Grampus griseus ) and killer whale ( Orcinus orca ) can be included in the cosmopolitan species with locally abundant populations. Eight species of Balaenopteridae and eight ziphiids are common to cold waters of both sides of South America. However, the pygmy beaked whale Mesoplodon peruvianus has been recorded only from Peruvian waters of South America (also recorded from México and California) and a recently described species, Bahamonde’s beaked whale M. bahamondi, from the Juan Fernández Archipelago, Chile.

The dynamics of oceanographic and biological processes that sustain the high productivity of the Peruvian ecosystem can be dis-turbed by what has been called the El Niño southern oscillation (ENSO event), whose main characteristic is the infl ow of tropical waters into the upwelling region around December ( Reyes, 1992 ).The nature of ENSO is irregular and unpredictable, and the impact on the intermediate levels of the food chain (e.g., abundance of anchovies) affects seabirds and marine mammals. Demonstrated effects of ENSO events on fur seals, sea lions, dusky dolphins, and seabirds, have included those on survival, recruitment, and the gen-eral condition of the individuals as a consequence of reduced food availability. An ENSO event is part of a more general pattern of oceanographic change affecting not only the Peruvian ecosystem but also the entire Southern Ocean.

encyclopedia of marine mammals || sound production

Documents

name:! ! unit 3 –regression and correlation › uploads...

long island sound blue plan – potential data …...long...

encyclopedia of marine mammals - cascadia research · of...

revision transport in mammals. transport in mammals

sustainable urban sound design urban sound design ......

introduction to mammals and diversity of mammals

class mammalia (mammals )(mammals ) mammals are adapted to...

acoustics - marine mammals€¦ · acoustics...

mechanisms of sound localization in mammals · mechanisms...

mammals are we mammals?. what will we learn? we will learn:...

anthropogenic sound and marine mammals in the...

2015 04 27 review of masking report 12 · 2016. 6. 21. ·...

7367795 longman s encyclopedia mammals

the amazing dromedary cameldromedary camels are mammals...

grzimek animal life encyclopedia volume 13 mammals ii

marine mammals and noise fact sheet - boem homepage ·...

__________________ mammals. marine mammals mammals found in...

diversity of mammals placental mammals

encyclopedia of marine mammals - false killer whales ·...

grzimek animal life encyclopedia volume 15 mammals iv