Monitoring animal diversity using acoustic indices: Implementation in a temperate woodland (original) (raw)
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Acoustic Indices for Biodiversity Assessment and Landscape Investigation
Acta Acustica united with Acustica, 2014
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. scale shedding newl ight on the acoustic behaviour and acoustic ecology of animals.
Rapid acoustic surveys aim to estimate biodiversity based on the diversity of sounds produced by animal communities , and interest in this approach among conservation planners is increasing. Several indices of acoustic diversity have been proposed as proxies for species richness. However, in the field, the animal activity may be responsible for acoustic diversity to varying degrees. To evaluate how measures of acoustic diversity may depart from actual species richness, we selected seven acoustic indices and applied them to simulated recordings of bird assemblages under different field conditions. For a given sound, defined here as the song composition emitted by a species assemblage, we determined if the indices were i) only driven by animal sounds, ii) insensitive to species identity, and iii) independent of species evenness. Under the field conditions evaluated, none of the indices fulfilled the three criteria necessary for a perfect proxy of species richness. However, some indices may be appropriate as a measure of biodiversity under a more broad definition including phylogenetic and/or functional aspects of diversity. We provide recommendations for the application of these indices for biodiversity measurement under field conditions, such as the application of appropriate audio filters, the increase of the repetition rate of the recordings, and the identification of the main taxonomic groups occurring in the recorded communities.
Rapid assessment of biodiversity using acoustic indices
Biodiversity and Conservation, 2018
The evolutionary success of a species is linked to its ability to communicate. Auditory, optic and olfactory systems are biological communication channels. Compared to the latter two, auditory systems are less impeded by physical obstructions. Successful species have effectively articulated this to their advantage. Decoding the acoustic dynamics of a landscape can ingeniously be crafted as a rapid tool to assess biological diversity. Here, we present results of the acoustic analysis carried out in three contrasting soundscapes in Kerala, India. Representative sound samples were recorded at Ernakulam, Kerala, India using Marantz PMD 661 III sonic recorder from 6.00 a.m. to 6.00 p.m. (IST) from an urban park [Hill Palace Museum (L1)], a sacred grove [Iringole Kavu (L2)], and a legally protected area Salim Ali Bird Sanctuary (L3). Acoustic characteristics of these sites expressed as Acoustic Complexity Index (ACI), Acoustic Diversity Index (ADI), Acoustic Evenness Index (AEI), Bioacoustic Index (BI) and Normalized Difference Soundscape Index (NDSI) were related to corresponding avian diversity. The objective finding reveals the distinctiveness of sonic characteristics and the status of diversity in each soundscape. Rapid assessment of biodiversity using acoustic indices is a prospective option that can be adopted as a means to generate biodiversity indicators of Sustainable Develeopment Goals (SDGs).
Rapid Acoustic Survey for Biodiversity Appraisal
PLoS ONE, 2008
Biodiversity assessment remains one of the most difficult challenges encountered by ecologists and conservation biologists. This task is becoming even more urgent with the current increase of habitat loss. Many methods-from rapid biodiversity assessments (RBA) to all-taxa biodiversity inventories (ATBI)-have been developed for decades to estimate local species richness. However, these methods are costly and invasive. Several animals-birds, mammals, amphibians, fishes and arthropods-produce sounds when moving, communicating or sensing their environment. Here we propose a new concept and method to describe biodiversity. We suggest to forego species or morphospecies identification used by ATBI and RBA respectively but rather to tackle the problem at another evolutionary unit, the community level. We also propose that a part of diversity can be estimated and compared through a rapid acoustic analysis of the sound produced by animal communities. We produced a and b diversity indexes that we first tested with 540 simulated acoustic communities. The a index, which measures acoustic entropy, shows a logarithmic correlation with the number of species within the acoustic community. The b index, which estimates both temporal and spectral dissimilarities, is linearly linked to the number of unshared species between acoustic communities. We then applied both indexes to two closely spaced Tanzanian dry lowland coastal forests. Indexes reveal for this small sample a lower acoustic diversity for the most disturbed forest and acoustic dissimilarities between the two forests suggest that degradation could have significantly decreased and modified community composition. Our results demonstrate for the first time that an indicator of biological diversity can be reliably obtained in a non-invasive way and with a limited sampling effort. This new approach may facilitate the appraisal of animal diversity at large spatial and temporal scales.
Rapid assessment of avian species richness and abundance using acoustic indices
Ecological Indicators, 2020
Accelerating global shifts in climate and land use change are altering natural habitats and species assemblages, making management interventions crucial to halt the biodiversity crisis. Management decisions must be informed by accurate biodiversity assessments. However, such assessments are often time consuming, expensive, and require specialist knowledge. Monitoring environmental sound may offer a novel method for rapid biodiversity assessment. Changes in species assemblages at a given location are reflected in the site's acoustic energy, termed the soundscape. Soundscapes can be readily described using acoustic indices; metrics based on objective features of recordings such as pitch and amplitude. Changes in acoustic indices values may therefore reflect changes in species assemblages, alerting land managers to shifts in wildlife populations. However, thus far, evidence supporting the use of acoustic indices in biodiversity monitoring has been equivocal. Here, we test the practical application of acoustic indices for biodiversity monitoring while solving methodological issues and providing conceptual clarity. Using 84 h of audio recordings covering 315 dawns from 43 sites, coupled with bird assemblage and vegetation data collected in the field, we demonstrate strong relationships between acoustic indices and avian species richness and abundance. In contrast with many previous studies, we found that sites with high bird speciesrichness and abundance had less even soundscapes (i.e. acoustic energy was less evenly distributed among frequencies) compared with sites with low species richness and abundance. Crucially, these patterns were coherent across multiple acoustic indices, and across habitat types, emphasising their utility for monitoring. Acoustic indices sensitive to the frequencies at which birds sing are most useful for monitoring avian communities; the Acoustic Evenness Index, Biophony Index, and the biophony component of the Normalised Difference Soundscape Index exhibited the strongest relationship with species richness. Land managers can use acoustic indices for biodiversity monitoring, complementing other, more established, assessment methods.
Ecological Indicators
Affordable, autonomous recording devices facilitate large scale acoustic monitoring and Rapid Acoustic Survey is emerging as a cost-effective approach to ecological monitoring; the success of the approach rests on the development of computational methods by which biodiversity metrics can be automatically derived from remotely collected audio data. Dozens of indices have been proposed to date, but systematic validation against classical, in situ diversity measures are lacking. This study conducted the most comprehensive comparative evaluation to date of the relationship between avian species diversity and a suite of acoustic indices. Acoustic surveys were carried out across habitat gradients in temperate and tropical biomes. Baseline avian species richness and subjective multi-taxa biophonic density estimates were established through aural counting by expert ornithologists. 26 acoustic indices were calculated and compared to observed variations in species diversity. Five acoustic diversity indices (Bioacoustic Index, Acoustic Diversity Index, Acoustic Evenness Index, Acoustic Entropy, and the Normalised Difference Sound Index) were assessed as well as three simple acoustic descriptors (Root-mean-square, Spectral centroid and Zero-crossing rate). Highly significant correlations, of up to 65%, between acoustic indices and avian species richness were observed across temperate habitats, supporting the use of automated acoustic indices in biodiversity monitoring where a single vocal taxon dominates. Significant, weaker correlations were observed in neotropical habitats which host multiple non-avian vocalizing species. Multivariate classification analyses demonstrated that each habitat has a very distinct soundscape and that AIs track observed differences in habitat-dependent community composition. Multivariate analyses of the relative predictive power of AIs show that compound indices are more powerful predictors of avian species richness than any single index and simple descriptors are significant contributors to avian diversity prediction in multi-taxa tropical environments. Our results support the use of community level acoustic indices as a proxy for species richness and point to the potential for tracking subtler habitat-dependent changes in community composition. Recommendations for the design of compound indices for multi-taxa community composition appraisal are put forward, with consideration for the requirements of next generation, low power remote monitoring networks.
Acoustic indices applied to biodiversity monitoring in a Costa Rica dry tropical forest
Journal of Ecoacoustics, 2018
Standardized methods for biodiversity monitoring are needed to evaluate conservation efforts. Acoustic indices are used in biodiversity assessments, but need to be compared to traditional wildlife methods. This work was conducted in the Santa Rosa National Park between June and November, 2015. We installed recorders and conducted bird point counts in twelve sampling sites. We compared acoustic indices (Acoustic Evenness Index [AEI], Acoustic Diversity Index [ADI], Acoustic Complexity Index [ACI], Bioacoustic Index [BIO], Normalized Difference Soundscape Index [NDSI], Total Entropy [TE], Median Amplitude Envelope [MAE], Number of peaks [NP]) with indices from bird point counts (Bird Abundance, Bird Richness, Bird Diversity and Bird Evenness), and discuss the utility of acoustic indices as indicators for biodiversity monitoring in tropical forests. ADI, ACI, BIO and TE presented a similar temporal pattern peaking between 5 am and 6 am; and an additional peak at 5 pm, except for ACI. T...
Connecting soundscape to landscape: Which acoustic index best describes landscape configuration?
Soundscape assessment has been proposed as a remote ecological monitoring tool for measuring biodiversity, but few studies have examined how soundscape patterns vary with landscape configuration and condition. The goal of our study was to examine a suite of published acoustic indices to determine whether they provide comparable results relative to varying levels of landscape fragmentation and ecological condition in nineteen forest sites in eastern Australia. Our comparison of six acoustic indices according to time of day revealed that two indices, the acoustic complexity and the bioacoustic index, presented a similar pattern that was linked to avian song intensity, but was not related to landscape and biodiversity attributes. The diversity indices, acoustic entropy and acoustic diversity, and the normalized difference soundscape index revealed high nighttime sound, as well as a dawn and dusk chorus. These indices appear to be sensitive to nocturnal biodiversity which is abundant at night in warm, subtropical environments. We argue that there is need to better understand temporal partitioning of the soundscape by specific taxonomic groups, and this should involve integrated research on amphibians, insects and birds during a 24 h cycle. The three indices that best connected the soundscape with landscape characteristics, ecological condition and bird species richness were acoustic entropy, acoustic evenness and the normalized difference soundscape index. This study has demonstrated that remote soundscape assessment can be implemented as an ecological monitoring tool in fragmented Australian forest landscapes. However, further investigation should be dedicated to refining and/or combining existing acoustic indices and also to determine if these indices are appropriate in other landscapes and for other survey purposes.
Sound-mapping a coniferous forest-Perspectives for biodiversity monitoring and noise mitigation
PloS one, 2018
Acoustic diversity indices have been proposed as low-cost biodiversity monitoring tools. The acoustic diversity of a soundscape can be indicative of the richness of an acoustic community and the structural/vegetation characteristics of a habitat. There is a need to apply these methods to landscapes that are ecologically and/or economically important. We investigate the relationship between the acoustic properties of a coniferous forest with stand-age and structure. We sampled a 73 point grid in part of the UK's largest man-made lowland coniferous plantation forest, covering a 320ha mosaic of different aged stands. Forest stands ranged from 0-85 years old providing an age-gradient. Short soundscape recordings were collected from each grid point on multiple mornings (between 6am-11am) to capture the dawn chorus. We repeated the study during July/August in 2014 and again in 2015. Five acoustic indices were calculated for a total of 889 two minute samples. Moderate relationships bet...