Bioacoustics is historically adiscipline that essentially focuses on individual behaviour in relation to population and species evolutionary levels butr arely in connection with higher levels of ecological complexity likec ommunity,landscape or ecosystem. However, some recent bioacoustic researches have operated ac hange of scale by developing acoustic indices which aim is to characterize animal acoustic communities and soundscapes. We here reviewt hese indices for the first time. The indices can be divided into twoc lasses: the α or within-group indices and the β or between-group indices. Up to 21 α acoustic indices were proposed in less than six years. These indices estimate the amplitude, evenness, richness, heterogeneity of an acoustic community or soundscape. Seven β diversity indices were suggested to compare amplitude envelopes or,more often, frequencyspectral profiles. Both α and β indices reported congruent and expected results buttheymay still suffer some bias due, for instance, to anthropic background noise or variations in the distances between vocalising animals and the sensors. Research is still needed to improve the reliability of these newmathematical tools for biodiversity assessment and monitoring. We recommend the contemporary use of some of these indices to obtain complementary information. Eventually,weforesee that this newfield of research which tries to build bridges between animal behaviour and ecology should meet an important success in the next years for the assessment and monitoring of marine, freshwater and terrestrial biodiversity from individual-based leveltolandscape dimension.
When animals live in cities, they have to adjust their behaviour and life histories to novel environments. Noise pollution puts a severe constraint on vocal communication by interfering with the detection of acoustic signals. Recent studies show that city birds sing higher-frequency songs than their conspecifics in non-urban habitats. This has been interpreted as an adaptation to counteract masking by traffic noise. However, this notion is debated, for the observed frequency shifts seem to be less efficient at mitigating noise than singing louder, and it has been suggested that city birds might use particularly high-frequency song elements because they can be produced at higher amplitudes. Here, we present the first phonetogram for a songbird, which shows that frequency and amplitude are strongly positively correlated in the common blackbird (Turdus merula), a successful urban colonizer. Moreover, city blackbirds preferentially sang higher-frequency elements that can be produced at higher intensities and, at the same time, happen to be less masked in low-frequency traffic noise.
The study of marine soundscapes is an emerging field of research that contributes important information about biological compositions and environmental conditions. The seasonal and circadian soundscape trends of a marine protected area (MPA) in the Mediterranean Sea have been studied for one year using an autonomous acoustic recorder. Frequencies less than 1 kHz are dominated by noise generated by waves and are louder during the winter; conversely, higher frequencies (4–96 kHz) are dominated by snapping shrimp, which increase their acoustic activity at night during the summer. Fish choruses, below 2 kHz, characterize the soundscape at sunset during the summer. Because there are 13 vessel passages per hour on average, causing acoustic interference with fish choruses 46% of the time, this MPA cannot be considered to be protected from noise. On the basis of the high seasonal variability of the soundscape components, this study proposes a one-year acoustic monitoring protocol using the soundscape methodology approach and discusses the concept of MPA size.
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