Yager, D.D. (1992). Underwater acoustic communication in the African Pipid frog Xenopus borealis. Bioacoustics 4(1): 1-24
Abstract
The totally aquatic African pipid frog Xenopus borealis produces a range of acoustic signals underwater at night.
The repertoire of males in heightened reproductive condition consists of three call types. All of the calls are composed of the same impulsive, click-like components. The clicks have a rise-time of 0.5 msec, a duration of 2-5 msec, and most of their energy concentrated at 2600 Hz with a secondary peak at 1100 Hz.
The sound pressure levels average 109 dB SPL at 1 meter. The advertisement call is characterized by interclick intervals of 300-600 msec (depending on temperature) and very low coefficients of variation - 3%-10%). Phonotaxis experiments confirm that it is effective in attracting females. The approach call, produced when swimming toward or clasping another frog, has interclick intervals averaging 105 msec. Males show pronounced agonistic behavior accompanied by series of clicks with interclick intervals averaging 43 msec.
Unreceptive females sometimes produce a very weak release call when clasped, but are otherwise silent.
Comparison of this underwater acoustic communication system with terrestrial anuran systems shows surprisingly few differences, given the strong contrast in acoustic environments. The structure of the male's clicks, however, suggests that a major adaptation to underwater signalling may involve the sound production mechanism itself.
Robisson, P. (1992). Roles of pitch and duration in the discrimination of the mate's call in the King penguin Apenodytes patagonicus. Bioacoustics 4(1): 25-36
Abstract
Discrimination of the mate's call was studied in the king penguin Apenodytes patagonicus by considering two single parameters, syllable duration and pitch, both predicted by the acoustic analysis to be potentially involved in the identification process. The within-individual variation for syllable durations (average coefficient of variation: 4.3%) was 2.9 times smaller than the variation between individuals. The recognition was however not significantly altered by an alteration of the syllable duration of 20%. The mean within-individual variation for pitch (averaging coefficient of variation: 1.6%) was 4.3 times smaller than the variation between individuals. An alteration of the pitch as much as 10% was however necessary to hamper the recognition. Role of the two parameters in the discrimination of the mate's call are discussed in view of the knowledge about the auditory duration and pitch discrimination in birds, as well as their potential integration in the decision rules.
McGregor, P.K. & Byle, P. (1992). Individually distinctive bittern booms: potential as a census tool. Bioacoustics 4(2): 93-109
Abstract
Assessment of the similarity of sound spectrograms of the loud advertising vocalizations of bitterns (booms) by observers using subjective, qualitative criteria shows that the booms of bitterns are individually distinctive. Multivariate quantitative measures also showed booms to be individually distinctive. Both qualitative and quantitative assessments showed that booms from the same individual are consistent within and between years. The usefulness of individual distinctiveness in vocalizations for collecting data on within and between year survival is discussed, as are the factors limiting the technique.
Farabaugh, S.M., Brown, E.D. & Dooling, R.J. (1992). Analysis of the warble song of the budgerigar Melopsittacus undulatus. Bioacoustics 4(2): 111-130
Abstract
In this study we present a preliminary analysis of the structure of the complex multisyllabic warble song of the budgerigar Melopsittacus undulatus, a small, flock-living parakeet. We recorded eight male budgerigars from three different social groups, and one female. Budgerigar warble songs consist in long sequences of syllables that are diverse in structure, ranging from simple clicks to multinote, frequency-modulated musical-sounding syllables. We identified 42 syllable classes. Males shared a significantly greater percentage of their warble syllable-class repertoire with males in the same social group than with males in different groups. One male budgerigar preferentially imitated the syllables and temporal pattern of the abnormal warble of his cagemate (a male bird that had been reared in acoustic and social isolation) rather than the normal warble of other male budgerigars in adjoining cages. We discuss vocal imitation of social companions as a process of vocal learning, the potential role of warble song in individual and group recognition, and implications for syntactical structure of budgerigar warble song.
Ladich, F., Bischof, C., Schleinzer, G. & Fuchs, A. (1992). Intra- and interspecific differences in agonisitic vocalizations in croaking gouramis (Genus: Trichopsis, Anabantoidei, Teleostei). Bioacoustics 4(2): 131-141
Abstract
In this study a detailed analysis of acoustical parameters of sounds produced by male Trichopsis vittatus, T. schalleri and T. pumilus during agonistic behaviour is reported. The calls consist of croaks which are composed of double pulses generated by modified pectoral fins. Calls of the three species are different in main frequency, number of double pulses within a croak and double pulse period. Croaks are uttered in series only in T. vittatus. Sound pressure levels are highest in T. pumilus, the smallest species. Amplitude of individual pulses of a double pulse are similar in T. pumilus and T. schalleri. Main frequency is negatively correlated with body mass in all species, but there is no correlation between sound pressure level and body mass. Differences in the calls of the three species suggest that T. schalleri is a distinct species. Furthermore, results indicate spectral characteristics and sound intensity could be of biological importance in fish.
ten Cate, C. (1992). Coo types in the collared dove Streptopelia decaocto; one theme, distinctive variations. Bioacoustics 4(3): 161-183
Abstract
Dove coos are known to be important for intra-specific communication in various contexts. Earlier research showed the occurrence of systematic frequency modulations for the perch-coo of the collared dove and suggested that presence or absence of these modulations might be important in communication. The present study examined the occurrence of frequency modulations and frequency use for perch-, bow- and nest-coo, as well as variation in these features between and within individuals, to assess the acoustic ‘signal space' for this species. The occurrence of frequency modulations was high for perch- and bow-coo, but low for the nest-coo. The relative distribution of modulations over the three elements of a coo differed for the various coo types. Coo types differed also in their ‘frequency profiles'. Frequency use is correlated with the occurrence of modulations. Differences between coo-types as well as variation within a coo-type and within individuals can be described by a limited set of parameters, which may be linked to basic properties of the coo producing mechanism. As a consequence of the occurrence of modulations and their distribution over the coo-types, the acoustic differences between the coo-types are amplified. As the different coo-types serve different functions, presence of modulations increases the signal space and decreases the ambiguity of the coo types. Differences between individuals exceeded those within individuals and were largest for perch- and bow-coo, which both serve in territorial defence and mate attraction.
Enggist-Dublin, P. & Birkhead, T.R. (1992). Differences in the calls of European and North American black-billed magpies and the yellow-billed magpie. Bioacoustics 4(3): 185-194
Abstract
We compared several features of the chatter call of two races of black-billed magpies, the nominate, European race Pica pica pica and the North American race P. p. hudsonia and the yellow-billed magpie P. nuttalli. The chatter calls of the two North American species were much more similar to each other than either was to the European magpie. This information together with the recently determined similarities in the behaviour and social organisation of the two North American species, suggests that the phylogenetic affinities of these two species are closer than is implied by their taxonomic status.
Watkins, W.A. & Daher, M.A. (1992). Underwater sound recording of animals. Bioacoustics 4(3): 195-209
Abstract
Underwater sound recording of animals uses specialized techniques to obtain faithful copies of sounds produced by animals during their normal activities underwater. Techniques have to be unobtrusive as well as nondisturbing to avoid changing the animal behaviors. The first scientific recording of underwater sounds from a marine mammal at sea was by William E. Schevill and Barbara Lawrence in 1948. Although the equipment has changed considerably since then, the techniques, approaches to animals and environmental impedimenta have remained essentially the same. However, the frequency and dynamic ranges of underwater sounds can easily exceed terrestrial sounds, so the selection of suitable equipment is critical. The elements of a useful system for bioacoustic recording of marine animals include the hydrophone, impedance transformer/preamplifier, cable, signal amplifier, recorder and sound monitor. The important criteria for each of these is discussed, along with directional listening systems, and the need for calibrations to verify the performance of the entire underwater recording system. For each situation, the ideal system is the one with the best compromise of interactive component to record that particular sound spectrum.
Luschi, P. (1993). Improvisation of new notes during singing by male Sardinian warblers Sylvia melanocephala. Bioacoustics 4(4): 235-244
Abstract
The songs of Sardinian warblers Sylvia melanocephala are extremely complex and variable, and even consecutive songs uttered by the same male usually differ. To provide a better understanding of the nature of the variation recorded, an attempt has been made to determine size and composition of the note repertoire of three selected individuals. The analysis was carried out on samples each consisting of several dozen songs, and the various notes were sorted on the basis of the visual similarity of their spectrographic patterns. Each male turned out to have a very large note repertoire which does not show any overlap with those of other males, with the only exception a particular note found in the songs of all the males. In two birds out of three, however, the graphs of the occurrence of new notes in consecutive songs show no tendency to become asymptotic. This suggests that the assessment of note repertoire size in these birds is not accurate, as they continue inserting new notes in their songs even after they have uttered several dozen songs. A table recording the presence or absence of the various notes in consecutive songs revealed that at least two of the three birds used different sets of notes in different bouts of songs, switching from one to another after short pauses made between two consecutive bouts. All this makes the attempt to assess the actual size of the note repertoire in these birds very difficult, and makes it probable that Sardinian warblers do not possess a finite repertoire of notes. The pattern of note selection observed for the three males in this study is best explained by assuming that these birds improvise new notes as they sing.
Terhune, J.M., Burton, H. & Green, K. (1993). Classification of diverse call types using cluster analysis techniques. Bioacoustics 4(4): 245-258
Abstract
We investigated the problem of categorizing the repertoire of a group of highly varied vocalizations. A set of Weddell seal Leptonychotes weddelli in-air calls recorded near Davis, Antarctica, were examined. The repertoire size was estimated by first subjectively assigning each call (based on auditory and spectrographic patterns) to one of a large number of provisional call types. A set of frequency, duration and waveform measurements were made on every call. For each provisional call type, the mean value of each of these measures was calculated. These mean values were used to perform Cluster Analyses of the provisional call types. Beginning with calls clustered closest together, the most similar provisional call types were successively amalgamated until further joining would link two clearly dissimilar vocalizations (rising versus falling frequency sweeps in thiscase). The Weddell seal repertoire contained 12 call types ranging from long sinusoidal upsweeps to growls. This procedure provides a method of estimating the minimum repertoire size of a sample of calls. Dichotomous Sorting using Principal Components Analysis can also be used to categorize calls but will probably be of greater value when applied to finding subdivisions within a single call type.
Forrest, T.G., Miller, G.L. & Zagar, J.R. (1993). Sound propagation in shallow water: implications for acoustic communication by aquatic animals. Bioacoustics 4(4): 259-270
Abstract
Measurements of sound propagation were made in a shallow, sloping bottomed freshwater pond. The frequency responses of the pond had a highpass characteristic with a sharp cut-off frequency. Cut-off frequency of the response was inversely related to the depth of water at the shallowest transducer (either projector or receiver) and was the same whether propagating downslope or upslope (reciprocity). The relationship between cut-off frequency and depth was significantly different from that expected for propagation in a channel with either a rigid or pressure release (gas) bottom. The highways characteristic is due to modal propagation in the 'waveguide', and the effect of this environmental filtering is 30-60 dB between frequencies that propagate and those that do not. Thus, the physical constraints of this shallow-water environment on acoustic communication by aquatic animals are much greater than those measured in terrestrial environments. These constraints are discussed relative to selection for behavioural adaptations of acoustically signalling aquatic animals and are compared to similar adaptations found in terrestrial systems.
Pye, J.D. (1993). Is fidelity futile? The "true" signal is illusory, especially with ultrasound. Bioacoustics 4(4): 271-286
Abstract
No matter how perfect the recording equipment may be, there are acoustical influences that change signals in various ways. It may become impossible to decide just what the ‘real' signal is like in detail for there may be no simple answer. Such considerations can relate to any examples of communication but they become especially significant for ultrasound and may pose important problems for echolocation.