31 research outputs found

    The Acoustic Structure and Information Content of Female Koala Vocal Signals

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    <div><p>Determining the information content of animal vocalisations can give valuable insights into the potential functions of vocal signals. The source-filter theory of vocal production allows researchers to examine the information content of mammal vocalisations by linking variation in acoustic features with variation in relevant physical characteristics of the caller. Here I used a source-filter theory approach to classify female koala vocalisations into different call-types, and determine which acoustic features have the potential to convey important information about the caller to other conspecifics. A two-step cluster analysis classified female calls into bellows, snarls and tonal rejection calls. Additional results revealed that female koala vocalisations differed in their potential to provide information about a given caller’s phenotype that may be of importance to receivers. Female snarls did not contain reliable acoustic cues to the caller’s identity and age. In contrast, female bellows and tonal rejection calls were individually distinctive, and the tonal rejection calls of older female koalas had consistently lower mean, minimum and maximum fundamental frequency. In addition, female bellows were significantly shorter in duration and had higher fundamental frequency, formant frequencies, and formant frequency spacing than male bellows. These results indicate that female koala vocalisations have the potential to signal the caller’s identity, age and sex. I go on to discuss the anatomical basis for these findings, and consider the possible functional relevance of signalling this type of information in the koala’s natural habitat.</p></div

    Waveforms and spectrograms of female koala vocalisations.

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    <p>Spectrogram settings: Fast Fourier Transform (FFT) method; window length = 0.03 s; time step = 0.002; frequency step = 20 Hz; Gaussian window shape; dynamic range = 40 dB. The two-step cluster analysis and grouped female tonal rejection calls squawks (b), squeaks (c), wails (d) and screams (e), together. Bellows (a) and snarls (f) were separately clustered as discrete call-types. NLP is signified as follows: DC = deterministic chaos, BP = biphonation, SH = subharmonics.</p

    Comparison of means between acoustic features of male and female koala bellows.

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    <p>Significant differences are highlighted in bold.</p

    Comparison of female and male bellow inhalation sections.

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    <p>Spectrogram settings: Fast Fourier Transform (FFT) method; window length = 0.03 s; time step = 0.002; frequency step = 20 Hz; Gaussian window shape; dynamic range = 40 dB). The dark energy bands labelled (F1-F6) are the formant frequencies. Note that they are higher in female bellows.</p

    Age versus acoustic features of female koala vocalisations.

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    <p>Significant correlations are highlighted in bold. “<i>b”</i> = standardized beta coefficient.</p

    DFA structure matrix.

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    <p>The pooled within-groups correlations between discriminating variables and the first three standardized canonical discriminant functions are shown. Discriminating variables are ordered by absolute size of correlation within function. Correlation coefficients > 0.4 are shown.</p

    Tests of equality of group means between individuals for the acoustic measures derived from each of the three call-types.

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    <p>“-”= cannot be computed because this variable is constant.</p

    Spectrogram (A) and waveform (B) of a male fallow deer groan.

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    <p>Male fallow deer groans are low-pitched vocalisations characterised by a rapid downward shift in formant frequencies across the call (spectrogram settings: FFT method, window length = 0.05 s, time step = 0.01 s, Gaussian window shape, dynamic range = 30 dB).</p

    Estimated marginal means ± SE of male behavioural responses to the playback stimuli.

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    <p>Looking responses (a and b), bellow responses (c and d), latency to bellow (e) and bellow formant spacing (f) to the large and small adult male size variant conditions are shown. *<i>p</i> < 0.05.</p
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