Acoustic Indices for Biodiversity Assessment and Landscape Investigation

Bioacoustics is historically a discipline that essentially focuses on individual behaviour in relation to population and species evolutionary levels but rarely in connection with higher levels of ecological complexity like community, landscape or ecosystem. However, some recent bioacoustic researches have operated a change of scale by developing acoustic indices which aim is to characterize animal acoustic communities and soundscapes. We here review these indices for the first time. The indices can be divided into two classes: 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, frequency spectral profiles. Both α and β indices reported congruent and expected results but they may still suff er 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 new mathematical tools for biodiversity assessment and monitoring. We recommend the contemporary use of some of these indices to obtain complementary information. Eventually, we foresee that this new field 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 level to landscape dimension.