BIOACOUSTICSTable of Contents: Volume 8
BIOACOUSTICSSpecial issue on cetacean acoustics
Edited by Arthur N. Popper, Harold L. Hawkins and William Dolphin
Sam Ridgway (1997). Who are the whales? Bioacoustics 8(1-2): 3-20
Abstract
Whales, dolphins and porpoises, 80 species of entirely aquatic mammals, constitute the order Cetacea. In the early Eocene, about 55 to 60 million years ago according to paleontologists, distant ancestors of modern cetaceans left land for aquatic life. Cetaceans are diverse; average adult size of cetacean species varies by 1000 to 2000 times. Small and large species occupy all oceans from the equator to the polar seas, some forms inhabit rivers and four species live only in fresh water. Cetaceans are born in water and spend their entire lives in the aquatic medium. There is a great gap in knowledge about hearing in most cetacean species and especially about how noise and high-intensity sound may affect all cetaceans and other mammals underwater. Studies of temporary threshold shift (TTS) and occupational noise exposure in human divers suggest a cautious approach to cetacean noise exposure until data on cetacean TTS can give us some idea of the dynamic range of cetacean ears.
Keywords: whale, dolphin, porpoise, sound, TTS, cetacean, noise, diver, bubbles, bends, delphinoid, acoustic safety, audiogram, pollution, hearing, sound production.
Peter L. Tyack (1997). Development and social functions of signature whistles in bottlenose dolphins Tursiops truncatus. Bioacoustics 8(1-2): 21-46
Abstract
Bottlenose dolphins Tursiops truncatus produce individually distinctive signature whistles. Dolphins recognize the signature whistles of animals with which they share a social bond. Signature whistles develop within the first few months of life and are stable for a lifetime. Vocal learning appears to play a role in the development of signature whistles in bottlenose dolphins. The signature whistles of most female dolphins and about half of male dolphins differ from those of their mothers. Some dolphin calves born in captivity develop a signature whistle that matches either man-made whistles or those of an unrelated dolphin. Dolphins retain the ability as adults to imitate the whistles of animals with which they share strong individual-specific social relationships, bonds which may change throughout their lifetime. The exceptional imitative abilities of dolphin infants and the retention of this ability in adults may be related to the maintenance of changing individual-specific social relationships. Individual recognition by the voice may differ in marine vs terrestrial mammals. Diving marine mammals may not be able to rely upon involuntary voice cues for individual recognition, but rather may require vocal learning to maintain a stable signature as their vocal tract changes shape with increasing pressure during a dive.
Keywords: bottlenose dolphins, Tursiops truncatus, vocal development, vocal learning, signature whistle.
Peggy L. Edds-Walton (1997). Acoustic communication signals of mysticete whales. Bioacoustics 8(1-2): 47-60
Abstract
Mysticete (baleen) whales produce a variety of vocalizations and sounds, but relatively few of these have been well described with accompanying behavior. This review concentrates on the vocalizations consistently associated with behavioral interactions or acoustic exchanges between or among conspecifics. These communication “signals” have been categorized for this review as contact calls of single animals outside of the breeding season (including cow-calf pairs), vocalizations reported during the breeding season (often designated as ''songs''), and calls produced by active groups of whales that may or may not have a reproductive function. While much remains unknown, the data obtained thus far indicate that the social vocalizations of baleen whales have structural/functional similarities with those of other mammals and birds.
Keywords: baleen whales, communication, vocalization, contact calls, song
Patrick W. B. Moore (1997). Cetacean auditory psychophysics. Bioacoustics 8(1-2): 61-78
Abstract
The dolphin continues to capture the imagination of investigators because of its ability to echolocate. Echolocation is essentially a special extension and adaptation of the dolphin's hearing system, coupled with the animal's ability to generate special sounds. Humans have demonstrated the ability to judge room size based on reverberation from a voice, and some of the visually challenged use self-generated sounds to detect large reflective objects. Echolocation represents a highly refined acoustic ability on a broad acoustic sensory continuum. Research on the auditory and echolocation performance of cetaceans has moved forward slowly due to limited animal resources and the general high cost of maintaining these animals in a laboratory environment.
This paper reviews some of the more relevant psychoacoustic data on cetaceans, and concentrates on the bottlenose dolphin Tursiops truncatus. The information presented is not at all exhaustive. Early work with dolphins focused mainly on the animal's ability to use its echolocation system. Once echolocation capability was demonstrated using a blindfolded dolphin, the quest to understand dolphin sonar moved from qualifying the dolphin's echolocation skill to quantifying its basic capabilities.
Psychophysics, and more precisely psychoacoustics, provides the tools to study dolphin echolocation. The procedures, theories and even the apparatuses from the traditional psychoacoustics laboratory are adapted to the dolphin experimental setting to measure and analyze the sensory phenomenon of dolphin echolocation. Basic auditory phenomena such as the audiogram, the effects of masking, critical ratio and critical band, and interaural time and intensity discrimination capabilities have been explored in the dolphin. Additionally, special experiments investigating the psychoacoustics of the echolocation system in particular have been conducted.Keywords: psychophysics, dolphin, binaural hearing, thresholds
William Ford Dolphin (1997). Electrophysiological measures of auditory processing in odontocetes. Bioacoustics 8(1-2): 79-101
Abstract
The preponderance of our knowledge concerning hearing in the Cetacea has come from psychophysical studies. The most widely used alternative to psychophysical studies are neurophysiological studies utilizing auditory evoked potentials (AEPs). Due in part to the hypertrophy of auditory structures exhibited by the Cetacea, AEPS are highly robust and rapidly and easily obtained. Moreover, because AEPS reflect the synchronized activity of large neuronal assemblies, they offer a high level window onto auditory processing and allow for across-species comparison of responses.
Recent studies utilizing AEP techniques have demonstrated that the cetaceans have extremely high temporal resolution with integration times in the order of 300 msec. Remarkably, these animals also exhibit extremely sharp frequency tuning with auditory filters having Q10 of 20-30.Keywords: cetaceans, auditory evoked potentials; temporal integration; frequency resolution; hearing
Darlene R. Ketten (1997). Structure and function in whale ears. Bioacoustics 8(1-2): 103-135
Abstract
Ultrasonic echolocation abilities are well documented in several dolphin species, but hearing characteristics are unknown for most whales. Vocalization data suggest whale hearing spans infra- to ultrasonic ranges. This paper presents an overview of whale ear anatomy and analyzes 1) how whale ears are adapted for underwater hearing and 2) how inner ear differences relate to different hearing capacities among whales. Whales have adaptations for rapid, deep diving and long submersion; e.g., broad-bore Eustachian tubes, no pinnae, and no air-feed external canals, that impact sound reception. In odontocetes, two soft tissue channels conduct sound to the ear. In mysticetes, bone and soft tissue conduction are likely. The middle ear is air-filled but has an extensible mucosa. Cochlear structures are hypertrophied and vestibular components are reduced. Auditory ganglion cell densities are double land mammal averages (2000-4000/mm). Basilar membrane lengths range 20-70 mm; gradients are larger than in terrestrial mammals. Odontocetes have 20-60% bony membrane support and basal ratios >0.6, consistent with hearing >150 kHz. Mysticetes have apical ratios <0.002 and no bony lateral support, implying acute infrasonic hearing. Cochlear hypertrophy may be adaptive for high background noise. Vestibular loss is consistent with cervical fusion. Exceptionally high auditory fiber counts suggest both mysticetes and odontocetes have ears “wired” for more complex signal processing mechanisms than most land mammals.
Keywords: cetacean ear, inner ear, odontocete, mysticete, basilar membrane, cochlea, auditory system, auditory nerve
Whitlow W.L. Au (1997). Echolocation in dolphins with a dolphin-bat comparison. Bioacoustics 8(1-2): 137-162
Abstract
Dolphins possess a highly sophisticated auditory system and a keen capability for echolocation. Signals are emitted in the form of high intensity, short duration, broadband exponentially decaying pulses. The frequency spectra of echolocation signals used by many dolphins are dependent on the output intensity of the signals and not on any fine tuning by the animals. When the output intensity is low, the center frequency of the click tends to be low. As the output intensity increases, the center frequency also tends to increase. The pulses propagate from the dolphin's melon in a relatively narrow beam, and echoes are received via the lower jaw, with a slightly wider beam. Echolocating dolphins can detect targets at ranges of approximately 100 plus meters, depending on the size of the targets. Target discrimination experiments have shown that dolphins can discriminate the shape, size, material composition and internal structure of targets from the echoes. The broadband, short duration properties of the signal allow the echoes to have high temporal resolution, so that within the structure of the echoes a considerable amount of information on the properties of the target can be conveyed. A brief comparison between the bat and dolphin sonar system will also be made. Bats typically emit much longer signals and a wider variety of different types of signals than dolphins. Signals used by some bats are suited to detecting Doppler shift, whereas the dolphin signal is designed to be tolerant of Doppler effects.
Keywords: dolphin echolocation, bat echolocation, echolocation signals, target detection, target discrimination, detection threshold, discrimination threshold
Arthur N. Popper, Harold L. Hawkins and Robert C. Gisiner (1997). Questions in cetacean bioacoustics: some suggestions for future research. Bioacoustics 8(1-2): 163-182
Abstract
This paper provides our views on the areas of cetacean bioacoustics that are in the greatest need of study over the next several years. In doing this, we ask a number of questions we see as important to developing a better understanding of cetacean bioacoustics. The topics we will cover are: Auditory Capabilities, including hearing sensitivity, pathways of sound to the ear, intraspecific variation in hearing capabilities, and the effects of intense sound on hearing capabilities; Echolocation, including the information-bearing parameters exploited by dolphin sonar systems to discriminate and identify objects, and the functional characteristics of the internal representation generated by reflections from ensonified objects; and Acoustic Communication, including the nature of the cetacean sound generation mechanism, the behaviors associated with mysticete communication sounds, and the range over which mysticetes communicate. While other investigators may not fully agree with our suggestions as to which questions are most important for future studies of cetacean bioacoustics, it is clear that a considerable effort must still be made in order that we can better understand the bioacoustics and general behavior of these animals.
Keywords: odontocete, mysticete, whale, dolphin, hearing, ear, echolocation, communication, sound production, porpoise
F. Ladich (1997). Computer analysis of swimbladder (drumming) and pectoral (stridulation) sounds in three families of catfish. Bioacoustics 8(3-4): 185-208
Abstract
Among teleosts, only representatives of several tropical catfish families have evolved two sonic organs: pectoral spines for stridulation and swimbladder drumming muscles. Pectoral mechanisms differ in relative size between pimelodids, mochokids and doradids, whereas swimbladder mechanisms exhibit differences in origin and insertion of extrinsic muscles. Differences in vocalization among families were investigated by comparing distress calls in air and underwater. High frequency broad-band pulsed sounds of similar duration were emitted during abduction of pectoral spines in all three families. Adduction sounds were similar to abduction signals in doradids, shorter and of lower sound pressure in mochokids, and totally lacking in pimelodids. Simultaneously or successively with pectoral sounds, low frequency harmonic drumming sounds were produced by representatives of two families. Drumming sounds were of similar intensity as stridulatory sounds in pimelodids, fainter in doradids, and not present in mochokids. Swimbladder sounds were frequency modulated and the fundamental frequency was similar in pimelodids and doradids. The ratio of stridulatory to drumming sound amplitude was higher in air than underwater in both doradids and one of the pimelodids. Also, overall duration of pectoral sounds, compared to swimbladder sounds, was longer in air than underwater in one doradid and pimelodid species. This first comparison of vocalization within one major teleost order demonstrates a wide variation in occurrence, duration, intensity and spectral content of sounds and indicates family- and species-specific as well as context- (receiver-) dependent patterns of vocalization.
Keywords: catfishes, distress calls, family-typical vocalization, stridulation, drumming Sounds
G. Pavan, M. Priano, P. De Carli, A Fanfani & M. Giovannotti (1997). Stridulatory organ and ultrasonic emission in certain species of Ponerine ants (Genus Ectotomma and Pachychondyla, Hymenoptera, Formicidae). Bioacoustics 8(3-4): 209-221
Abstract
Five species of neotropical Ponerinae ants, Ectotomma permagnum Forel, E. quadridens Fabr., E. ruidum Roger, E. tuberculatum Olivier and Pachychondyla apicalis Latreille, were studied. The genus Ectotomma, consisting of 14 species in the tropical forests of Central and South America, has been studied previously in relation to the stridulation organ only. Stridulations were heard, in the four species considered in this paper, during artificial disturbance of individuals or of the whole colony; so the role of sound production during normal life is still uncertain. Pachychondyla apicalis, belonging to Central American forests, is occasionally present in cocoa and coffee plantations. The recordings made under laboratory conditions revealed the emission of pulse trains with very clear pulses extending in frequency to more than 75 kHz. The sounds recorded from the workers of the genus Ectotomma appeared homogeneous in their acoustic structure. They were typically emitted in long sequences and were made of pulse-trains consisting of two subunits (disyllabic chirps) characterized by pulses with opposite phase, produced by the alternate movement of the simple plectrum against the pars striders. In sounds recorded from workers of Pachychondyla we found sequences of monosyllabic chirps, made by single trains of pulses. Pictures and measurements on the stridulatory apparatus were made with a scanning electron microscope.
Keywords: stridulation, ultrasonic, ants, Ectatomma, Pachychondyla
S. Haftorn & J.P. Hailman (1997). Do the Siberian tits Parus cinctus in Scandinavia and Siberia speak the same language? Bioacoustics 8(3-4): 223-247
Abstract
The vocabulary of Siberian tits Parus cinctus in South Norway and East Siberia is compared by means of tape recordings and spectrograms. The species has many different calls that are greatly confused in the literature. In this paper ten main call types are examined. On the whole, the equivalent utterings are geographically so similar that a distinction is usually impossible or questionable. This similarity also applies to the contextual use of the calls. Consistent structural differences in certain calls were nevertheless found. The sit foraging call embraced on average a broader frequency range and was of a slightly longer duration in Siberia than in Norway. The complex ‘gargle' system could at both places be divided into three main groups equally represented in the populations: (1) trilled, (2) tonal and (3) simple gargles. The tonal gargles are characterized by a terminal tonal element (T) that varies in shape. In Norway, tonal gargles terminating with an even or upslurred T dominated, in Siberia those with a chevron-formed T. Historically, the west-east distribution throughout Eurasia was apparently continuous until quite recently, allowing an effective gene flow. Considering the huge distance from Norway to East Siberia and the markedly resident behaviour of the Siberian tit it is nevertheless somewhat unexpected that so few vocal differences have evolved. Several of the calls of the Siberian tit are structurally very similar to equivalent (most likely homologous) calls in other species belonging to the subgenus Poecile, e.g. the willow tit Parus montanus and the black-capped chickadee P. atricapillus, suggesting that the multicall repertoire of their common ancestor remained largely intact despite Poecile's differentiation into different species.
Keywords: Parus cinctus, Poecile subgenus, vocabulary, geographical variation