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J. L. Bower & C. W. Clark (2005). A field test of the accuracy of a passive acoustic location system. Bioacoustics 15(1): 1-14

Abstract

In this study, we tested the ability of a computer-based passive acoustic location system (ALS) to determine the two-dimensional locations of vocalizing animals. The ALS uses multi-track tape recordings to estimate locations based on arrival time delays between widely-spaced microphones. We tested the accuracy of ALS location estimates using tape recordings of wild free-ranging birds made with 4 microphones placed at the corners of a 40m square. We compared ALS location estimates for these birds with locations determined by surveying the locations of the perches birds vocalized from. ALS location estimates were typically less than 1m away from surveyed locations when birds vocalized within the square microphone array, rising to just over 2m for birds vocalizing from within 25m beyond the array boundary. Beyond 25m, accuracy diminished rapidly with increasing distance. ALS accuracy did not depend on the bird species located, but location estimates based on frequency modulated tonal notes were more than twice as accurate than those made using relatively unmodulated notes from the same songs. Two examples are given to demonstrate the usefulness of the ALS in field studies.

Keywords: array, acoustic location system, red-winged blackbird, song sparrow, bird song

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D. M. Logue, D. E. Gammon & M. C. Baker (2005). Minidisc recorders versus audiocassette recorders: a performance comparison. Bioacoustics 15(1): 15-33

Abstract

MiniDisc (MD) digital audio recorders have the potential to benefit bioacoustics research, but concerns about the ATRAC (Adaptive Transform Acoustic Coding) compression method employed by MD recorders have prevented their widespread acceptance in the research community. We compared the performance of MD recorders with that of professional grade audiocassette recorders. Test sounds were synthesized or recorded directly onto a computer hard drive and then transferred to each of two MD recorders and three cassette recorders. The sounds were then transferred back to a computer and compared to the original versions to quantify degradation caused by the recorders. MD recorders proved superior to cassette recorders in the accurate reproduction of mean frequency and the reproduction of low amplitude signals when a high amplitude signal occurred at a nearby frequency. Unlike audiocassette recorders, MD’s did not generate artefactual variance in signal frequency and amplitude. The new MD recorder used in our study consistently outperformed all other units in the ability to reproduce natural sounds, as quantified by two automated sound comparison techniques. We found, however, that MD recorders introduced acoustic artefacts after the rapid offset of signals. Artefact duration was not affected by signal duration, resulting in a positive relationship between signal duration and signal-to-noise ratio. The artefacts’ periodicity, duration, and amplitude depended on the frequency of the signal; high-frequency signals produced more periodic, shorter, and quieter artefacts than did low frequency signals. Recording amplitude has little to no effect on signal-to-noise ratio. Cassette recorders introduced non-periodic offset artefacts that were similar to the artefacts introduced by MD recorders after low frequency signals. We conclude that researchers should base their choice of a recording device on the types of sounds they intend to record and the relative importance of accurate reproduction of sound offset versus other aspects of recording fidelity. Overall, however, we see no compelling reason to avoid MD recorders for most field recording and playback applications, and we suggest that the study of bioacoustics stands to benefit from the many practical advantages and novel research methods afforded by this technology.

Keywords: ATRAC compression, audiocassette recorder, MiniDisc, recording fidelity, sound recording equipment.

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S. Hartwig (2005). Individual acoustic identification as a non-invasive conservation tool: an approach to the conservation of the African wild dog Lycaon pictus (Temminck, 1820). Bioacoustics 15(1): 35-50

Abstract

Individual variation in acoustic signals can be used for discrimination or identification purposes as a valuable supplement to radio-tagging and visual recognition. In this study, 721 hoo-calls from captive and free-ranging African wild dogs Lycaon pictus (n=9) were investigated for individual acoustic cues. The investigation applied a computer-aided sound analysis that allowed measurement of 93 parameters for each hoo-call. Discriminant function analyses demonstrated that the individuals differed in their call parameters primarily measured on the fundamental frequency. Additional discriminant analyses were run in order to find out if individuals can be re-identified once their hoo-calls are recorded and catalogued into a voice library. This procedure yielded an overall 67% correct assignment for the test data (ranging from 37% to 98% per individual), suggesting an above chance level re-recognition of individuals. The results establish the capability of re-identifying wild dogs using specific acoustic characteristics of their hoo-call, and suggest that this technique can be a useful tool in conserving this highly endangered species.

Keywords: Lycaon pictus, canids, individual acoustic distinctiveness, multiparametric sound analysis, voice library

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M. Lamml & B. Kramer (2005). Sound production in the reproductive behaviour of the weakly electric fish, Pollimyrus marianne Kramer et al. 2003 (Mormyridae, Teleostei). Bioacoustics 15(1): 51-78

Abstract

In addition to their electric organ discharges, two West African mormyrid species are known to generate sounds during reproduction. Here, we document the reproductive behaviour and concurrent vocalisations recorded in captive specimens of the new species Pollimyrus marianne from the Upper Zambezi River. Prior to spawning, three male P. marianne established a territory and built a nest of filamentous plant material each (that would hold eggs and larvae at a later stage). Beginning with territory establishment and usually at night, only the males generated two distinct vocalisations, a tonal moan (average duration, 2.26 ± SD 0.6 s), and a harsh grunt (0.596 ± SD 0.029 s; grunt pulse repetition rate, PRR, 32.1 ± SD 1.24 Hz at 25.4 ± SD 0.15 °C). Both vocalisation types were similar to, but clearly different from, those recorded in the two West African species, P. isidori and P. adspersus, the PRR (Pulse Repetition Rate) of which were higher by 25% and 60%, respectively (at similar temperature). At constant standard length, some of a male P. marianne’s sound characteristics varied only slightly over two years, but depended clearly on water temperature. When no other fish were present, the three males produced moans only sporadically. When, however, females were visiting, the males generated long-lasting moan sequences that were superimposed by grunts (moan-grunt bouts; average duration, 14.69 ± SD 2.2 s). The maximum rate of vocalisation occurred in the nights immediately before spawning; this rate receded when larvae were present in the nest, and vocalisations finally stopped after the larvae had dispersed. Vocalisation rate increased again when females restarted to visit the nest site. Long before and also after reproduction, territorial males vocalised with moans and some grunts, when territory intruders evoked escalating agonistic interactions that were correlated with many bites or butts. In agonistic contexts, moan duration, moan peak amplitude frequency and grunt pulse repetition rate differed from the sounds produced during courtship. In P. marianne, the generation of sounds during reproductive and agonistic interactions suggests a dual function: attraction of mates and threatening competing males, or potentially egg-eating females.

Key words: Acoustic communication, reproduction, spectral analysis, electric fish, vocalisation, aggression.

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J. S. Tripovich, T. L. Rogers & J. P. Y. Arnould. (2005). Species-specific characteristics and individual variation of the bark call produced by male Australian fur seals (Arctocephalus pusillus doriferus). Bioacoustics 15(1): 79-96

Abstract

Australian fur seals Arctocephalus pusillus doriferus are colonial breeding animals forming dense social groups during the breeding season. During this time, males establish and defend territories through physical conflicts, stereotyped posturing and vocalisations. While vocalisations are suggested to play an important role in male recognition systems, it has received little attention. Recordings of nine adult male Australian fur seals were made during the 2000 and 2001 breeding seasons at Kanowna Island (39° 10’S, 146° 18' E), Bass Strait, Australia. The in-air bark vocalisations of territory-holding males were used to characterise the Bark Call and to determine whether males produce individually distinct calls, which could be used as a basis for vocal recognition. Seventeen frequency and temporal variables were measured from a total of 162 barks from nine individual males. The Bark Series was more reliably classified (83%) to the correct caller compared to the Bark Unit. This was assigned with less certainty (68%), although the classification was still relatively high. Findings from this study indicate that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition in male Australian fur seals.

Keywords: Australian fur seals, males, vocalisations, individual variation, barks.

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J. D. Wood, B. McCowan, W. R. Langbauer Jr., J. J.Viljoen & L. A. Hart (2005).  Classification of African elephant Loxodonta africana rumbles using acoustic parameters and cluster analysis. Bioacoustics 15(2): 143-161

Abstract

It has been suggested that African savanna elephants Loxodonta africana produce 31 different call types (Langbauer 2000). Various researchers have described these calls by associating them with specific behavioural contexts. More recently Leong et al. (2003) have attempted to classify elephant call types based on their physical properties. They classified 8 acoustically distinct call types from a population of captive elephants. This study focuses on one of these call types, the rumble, in a wild population of elephants in Kruger National Park, South Africa. A single family group of elephants was followed to record group behaviours and vocalizations from January through August 2001. By measuring the physical properties of 663 rumbles and subjecting these to cluster analysis, we present evidence that shows that rumbles can be categorized by their physical properties and that the resulting rumble types are associated with specific group behaviours. We characterize three types of rumbles that differ significantly by ten acoustic parameters. Two rumble types were associated with the elephant group feeding and resting, while the third was associated with socializing and agitation.

Keywords: African elephant, Loxodonta africana, acoustic communication, call categorization, cluster analysis.

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V. Teloni, W. M. X. Zimmer & P. L. Tyack (2005). Sperm whale trumpet sounds. Bioacoustics 15(2): 163-174

Abstract

Sperm whale Physeter macrocephalus L. clicks have been studied for nearly fifty years, during which time great efforts have been made to understand the functions and production mechanisms of this sound. Other than clicks, sperm whales may also produce low intensity sounds arranged in short sequences, named trumpets, which have been recorded occasionally in the past by few groups of researchers. Sperm whale recordings collected in the Mediterranean Sea with a towed array and digital tags were used to describe the temporal and spectral characteristics of trumpets. This sound is made of a series of repeated units, around 0.2 s long, arranged in short sequences lasting between 0.6 s to 3.5 s. Each of these units comprises an amplitude modulated tonal waveform with a complex harmonic structure, and a spectrum composed of a low frequency component at 500 Hz and a mid-frequency component at 3 kHz. The apparent source level could be estimated for one of the trumpets and was estimated to be 172 dBpp re: 1μPa at 1m with energy flux density of 147 dB re: 1μ Pa²s.

Keywords: sperm whale sound, trumpeting, Physeter macrocephalus, Mediterranean Sea, sound production.

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Emanuel C. Mora, Annia Rodríguez, Silvio Macías, Iliana Quiñonez & Marcia M. Mellado (2005).The echolocation behaviour of Nycticeius cubanus (Chiroptera: Vespertilionidae): inter- and intra-individual plasticity in vocal signatures. Bioacoustics 15(2): 175-193

Abstract

We studied the echolocation behaviour of Nycticeius cubanus in the field in western Cuba. During hunting, N. cubanus search for insects emitting cries that sweep from 80 to 40 kHz in 4 to 12 ms. Search call characteristics correlate with the clutter structure of the hunting areas. Bats hunting in an uncluttered space broadcast longer and narrower signals, while bats hunting in cluttered space broadcast shorter and broadband signals. Longer calls were emitted with longer intervals while the duty cycle was kept below 15 % during search and approach phases. The call’s minimal frequency remained about 43 kHz showing variation coefficients of less than 3%. As a consequence, bandwidth correlates positively with the maximal frequency. Calls emitted by different sympatric individuals are accurately classified by sender using a discriminant function analysis, suggesting vocal signatures in N. cubanus. The statistical analysis of several passes of calls broadcast during the hunting activity of a single individual, demonstrates a high intra-individual plasticity in vocal signatures and points to a dynamic system.

Keywords: bats, echolocation, vocal signature, plasticity, Nycticeius cubanus

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P.T. Madsen, D.A. Carder, K. Bedholm & S.H. Ridgway (2005). Porpoise clicks from a sperm whale nose - convergent evolution of 130 kHz pulses in toothed whale sonars? Bioacoustics 15(2): 195-206

Abstract

Small toothed whales of the family Phocoenidae and delphinid genus Cephalorhynchus produce long-duration, narrowband biosonar clicks above 100 kHz, that might be seen as an adaptation for short range echolocation in shallow water. This paper presents data showing that the distantly related, and larger pygmy sperm whale Kogia breviceps (Kogiidae), that is a deep-diving, cephalopod-eating toothed whale, produce narrow-banded high frequency (NBHF) clicks identical to those of Phocoena and Cephalorhynchus (f0 = 130 kHz, Q3dB>10, duration > 80 msec). Thus, NBHF biosonarsignals have evolved on three independent occasions in the odontocete suborder, but the apparent functional convergence does not relate to anatomical or niche similarity. Rather, it is suggested that a biosonar strategy adapting to a minimum in ocean ambient noise above 100 kHz in concert with high Q auditory filters have led to convergent evolution of the NBHF biosonar clicks. Since these biosonar signals carry all their energy at frequencies above the upper hearing limit of the killer whale Orcinus orca, predator avoidance may also have been a evolutionary shaping factor of the sonar signals from these non-whistling odontocetes.

Keywords: Kogia, echolocation, biosonar, sound production, click

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V. Nityananda & R. Balakrishnan (2006). A diversity of songs among morphologically indistinguishable katydids of the genus Mecopoda (Orthoptera: Tettigoniidae) from Southern India. Bioacoustics 15(3): 223-250

Abstract

Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologically indistinguishable. Some of them were both sympatric and had synchronous breeding seasons. The songs of these five song types ranged from simple short chirps to highly complex songs with multiple components. The temporal patterns of the songs of the five song types were very distinctive, whereas their spectral features were similar. Component elements of the different songs were distinct despite overall similarity. The song types possibly represent sibling species.

Keywords: Mecopoda, katydid, cryptic species, morphometry, song types, India

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J. T. Tanttu, J. Turunen, A. Selin & M. Ojanen (2006). Automatic feature extraction and classification of crossbill (Loxia spp.) flight calls. Bioacoustics 15(3): 251-269

Abstract

In this paper a new method for the automatic classification of bird sounds is presented. Our method is based on acoustic parameters (features) taken from the first harmonic component computed from the sound spectrogram. The features are based on a line segment approximation of the first harmonic component. The final feature vectors, consisting of 16 real numbers, are then classified using a self-organizing map (SOM) neural network. Flight calls of four crossbill species (Loxia spp.) are used as a test example. In the first phase, an unsupervised network was trained and tested using common crossbill L. curvirostra flight calls recorded mainly in the Netherlands. The network was tested using two-barred L. leucoptera, Scottish L. scotica and parrot L. pytyopsittacus crossbill flight calls in the second phase. Finally, the results were validated applying the same network to flight calls of common crossbills and parrot crossbills recorded in Finland. The method automatically separated common crossbill flight calls from those of parrot crossbills. The classification accuracy of the Dutch recordings was 58% in the first phase and 54% in the second phase. The Finnish recordings were classified with 54% accuracy.

Keywords: automatic classification, crossbill, flight call, SOM

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M. H. Sawhney, M. C. Baker & B. R. Bisbee (2006). Development of Vocalisations in Nestling and Fledgling House Wrens in Natural Populations. Bioacoustics 15(3): 271-287

Abstract

We conducted a field study of the ontogeny of vocal signals in the house wren Troglodytes aedon during the nestling and fledgling phases of life. We did spectrographic analyses and quantification of the developmental changes that occurred in the acoustic features of the vocalisations. Evidence of progress to adult-like vocal patterns was of two types. First, nestling calls changed into a harsh sounding call that resembles the adult chatter call, functionally a warning call. Second, fledglings also uttered subsong, and these vocalisations were similar to notes typical of adult male song. When the vocalisations produced by developing young were broken down into their constituent vocal features, we found that the time course of development was not strictly linear. Instead of a unidirectional change through the course of nestling and fledgling life, the trajectories of the vocal features fluctuated through time and sometimes exhibited abrupt changes. These sudden shifts occurred during nestling life as well as at the time of fledging. We speculate on the possible causes of these abrupt transitions. Changes in acoustic features upon fledging appear to be linked to new social functions.

Keywords: ontogeny, vocalisations, house wren, Troglodytes aedon, nestlings, begging

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B. R. Mitchell, M. M. Makagon, M. M. Jaeger & R. H. Barrett (2006).Information Content of Coyote Barks and Howls. Bioacoustics 15(3): 289-314

Abstract

The information content of coyote (Canis latrans) vocalizations is poorly understood, but has important implications for understanding coyote behaviour. Coyotes probably use information present in barks or howls to recognize individuals, but the presence of individually-specific information has not been demonstrated. We found that coyote barks and howls contained individually specific characteristics: discriminant analysis correctly classified barks of five coyotes 69% of the time and howls of six coyotes 83% of the time. We also investigated the stability of vocalization characteristics at multiple distances from the source. Recordings were played back and re-recorded at 10 m, 500 m, and 1,000 m. Vocalization features were measured at each distance and analyzed to determine whether characteristics were stable. Most howl characteristics did not change with distance, and regardless of the distance discriminant analysis was 81% accurate at assigning howls among six individuals. Bark characteristics, however, were less stable and it is unlikely that barks could be used for individual recognition over long distances. The disparate results for the two vocalization types suggest that howls and barks serve separate functions. Howls appear optimized to convey information (i.e. data), while barks seem more suitable for attracting attention and acoustic ranging.

Keywords: bark, Canis latrans, Canidae, communication, coyote, distance effect, howl,
individual differences, ranging

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J. Kapusta, H. Szentgyörgyi, A. Surov, & G. Ryurikov (2006). Vocalization of Two Palaearctic Species of Hamster: Eversmann Hamster Allocricetulus eversmanni and Grey Hamster Cricetulus migratorius. Bioacoustics 15(3): 315-330

Abstract

This study compared the vocalization of two sympatrically occurring species of hamster: the Eversmann hamster Allocricetulus eversmann and the Grey hamster Cricetulus migratorius. The animals were tested in conspecific pairs for 5 min. Because of the high level of aggressiveness of both species, the hamsters were separated by a mesh partition, but they had olfactory, visual and acoustic contact. Female and male Eversmann hamsters vocalized more than those of Grey hamsters. This was expressed by emission of low-frequency calls as well as by ultrasounds. The difference in vocalization between the two species was also reflected in the basic structure of ultrasonic vocalizations. Grey hamster high-frequency (ultrasonic) pulses were longer and had larger bandwidths and lower minimum frequencies than Eversmann hamster calls. Within-species comparison of vocalization indicated that males of both species emitted fewer ultrasounds than females did. These differences could have an important role in communication within and between species living in the same area and preferring the same habitats.

Key words: Allocricetulus eversmanni, Cricetulus migratorius, Eversmann hamster, Grey hamster, ultrasonic calls, vocalization.

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