Soundscape Index Research Articles

Increased bird sound diversity in vineyards enhances visitors' tour experience

Abstract Biodiversity is rapidly declining, reducing the quantity and quality of human interactions with nature and constraining its contribution to human health and well‐being. Natural sounds are a key component of our experience of nature, but biodiversity losses are reflected in soundscapes, which are becoming less diverse and quieter. We characterised the soundscapes across 21 English vineyards using acoustic indices and related them to bird species richness and abundance. We found that higher bird species richness, but not abundance, led to more diverse and louder soundscapes, as reflected in higher values of Acoustic Complexity Index (ACI), Bioacoustic Index (BIO) and Normalised Difference Soundscape Index (NDSI), and lower values of Acoustic Entropy Index (H). Secondly, at three of the study vineyards that run vineyard tours, we measured visitors' experience of the tour in terms of sound enjoyment, soundscape connectedness and tour satisfaction and related these to ambient and experimentally enhanced soundscapes, where we used playback recordings of five additional birdsongs to increase the soundscapes' complexity and volume. Under ambient conditions, respondents' (n = 107) experience was significantly higher at sites with soundscapes that had higher ACI and BIO values, and lower H, Acoustic Diversity Index (ADI) and NDSI values, indicating a positive effect of more diverse and louder soundscapes. Natural sounds formed an important part of the tour experience at these sites, making visitors feel more present and connected to nature. Under experimental soundscape enhancement, respondents (n = 79) reported hearing significantly more bird species during the tour, and they reported significantly higher scores for sound enjoyment, soundscape connectedness and tour satisfaction than under ambient conditions. This effect was stronger in visitors who engaged more in pro‐environmental behaviours, such as purchasing organic foods. Our study demonstrates (i) the direct contribution of aural modes to our experience of nature and (ii) that the delivery of biodiversity conservation measures aimed at supporting bird diversity could simultaneously enhance the experience and well‐being benefits of spending time in nature. Natural soundscapes should therefore be recognised and valued as natural capital, and their protection should be incorporated into conservation planning and policy. Read the free Plain Language Summary for this article on the Journal blog.

Forest structural heterogeneity positively affects bird richness and acoustic diversity in a temperate, central European forest

IntroductionForests managed for timber production can also be managed for biodiversity conservation by retaining structures typical of old-growth forests, which provide heterogenous structures for forest-dwelling species, including birds. Ecoacoustic monitoring of forest birds is now a well-studied field, however the extent to which acoustic indices can reflect bird assemblage responses to stands of lower or higher structural heterogeneity is disputed. MethodIn this study, we acoustically surveyed 75 plots over two years in mature, previously managed forests and computed acoustic indices from the recordings. We first identified an acoustic index that significantly correlated with bird richness over more than one spring season. Next, we tested the response of bird richness to individual forest structural elements using linear regressions. We then repeated this analysis but combined the individual structural elements into one structural composition variable using an NMDS and gam smooth overlay, to compare the effect of individual forest structures versus overall forest heterogeneity on bird richness. We then repeated this analysis using our selected acoustic index, the Normalized Difference Soundscape Index (NDSI), to see if it followed the same patterns as bird richness in response to individual and collective forest structural elements.ResultsOur results showed that plots with high bird richness were also associated with high NDSI values, and high values of both variables occurred in plots with high structural heterogeneity (tree species richness, tree size variability, and snag height variability) and low amounts of standing and lying deadwood. DiscussionOur findings suggest that once an acoustic index can be identified as a robust correlate of bird richness, it can serve as a proxy for the response of birds to differences in forest structural heterogeneity within a managed forest context. It is therefore possible for forest managers interested in conserving or increasing bird richness in their production forests to identify a robust acoustic index to track the response of bird richness to management decisions over time.

The impact of a low traffic neighbourhood intervention on urban noise measured with low-cost sensors in Oxford, UK

Noise pollution, particularly in urban environments, is often caused by road traffic and is linked to increased risk of a range of adverse health outcomes. In recent years, Low Traffic Neighbourhoods (LTN) have been implemented in a number of UK towns and cities as an intervention to reduce road traffic and improve health and wellbeing among those living in residential areas. In this study, eight low-cost acoustic sensors (AudioMoth) were used to evaluate the effect of a LTN intervention on urban noise in a residential area of Oxford, UK. The acoustic energy and LAeq of the noise is evaluated before and after the introduction of the LTN at locations where traffic filters have been erected, other locations in the LTN, possible displacement locations, and a control location. In addition, source apportionment (anthropogenic or biotic) is undertaken using the Normalised Difference Soundscape Index (NDSI) using the frequency of the measured noise. The results show that in terms of acoustic energy almost all locations experienced a reduction in noise after the introduction of the LTN. In terms of the source apportionment, all locations except for the control location experienced more biotic noise after the introduction of the LTN. The results are also compared to other more traffic focussed locations in Oxford and the soundscape is much more biotic inside the LTN. Overall, the study demonstrates the impact of the LTN on urban noise, and the efficacy of this new sensing and analytical approach for evaluating noise pollution interventions.

Virtual Reality Technology in Analysis of the Sarek National Park Soundscape in Sweden

The paper presents an in-depth analysis of the soundscape within Sarek National Park, the oldest national park in Europe, situated in Lapland, northern Sweden. The comprehensive acoustic measurements, ambisonic recordings, and 360X video recordings were carried out during a scientific expedition in the summer of 2020. The aim of the paper is to show the soundscape analysis of carefully selected characteristic locations in various parts of the valley. The paper extensively discusses the findings derived from the recorded data using both classical acoustic methods and the soundscape approach. The classic acoustic parameters, commonly employed in environmental acoustics as well as eco-acoustic indices such as: ACI (acoustic complexity index), ADI (acoustic diversity index), AEI (acoustic evenness index), NDSI (normalized difference soundscape index), BIO (energy level of biophony), amplitude index (M), and total entropy (H) were calculated. To gain further insights, listening tests, facilitated through virtual reality tools, were conducted, enabling participants to engage in soundwalk experiences. By employing a combination of traditional acoustic methods and innovative soundscape approaches, the paper presents a holistic evaluation of the auditory environment in Sarek National Park. The main contribution of the presented research is providing new data from the unique, geographically inaccessible region of the world, the Sarek National Park. This research not only enriches our understanding of the national park’s soundscape but also offers valuable insights into the interaction between the natural environment and human perception of sound.

Hazardous wildfire smoke events can alter dawn soundscapes in dry forests of central and eastern Washington, United States

As global wildfire activity increases, wildlife are facing greater exposure to hazardous smoke pollution – with unknown consequences for biodiversity. Research on the effects of smoke on wild animals is extremely limited, in part due to the inherent logistical challenges of observing how animals respond to smoke in real time. Passive acoustic monitoring may be a powerful tool to safely and effectively monitor biodiversity before, during, and after major smoke events. In this study, we used data collected from a large-scale network of bioacoustic recorders at 92 sites in central and eastern Washington state during August–September, 2019–2020 to investigate the effect of wildfire smoke on dawn soundscapes and, by extension, acoustically active wildlife. We used acoustic indices to document and characterize changes in soundscapes related to smoke exposure, including the Acoustic Complexity Index (ACI), Bioacoustic Index (BI), and Normalized Difference Soundscape Index (NDSI). Higher values of these indices likely indicate higher levels of biodiversity in our study area. We hypothesized that wildfire smoke would reduce bird vocalizations, leading to declines in ACI, BI, and NDSI at dawn, when birds are most active. We used linear and quantile regression models to test for an effect of daily exposure to fine particulate matter (PM2.5), a marker of wildfire smoke, on the mean daily values and the upper 90th percentile of each index at dawn. We also conducted a before-during-after analysis of a particularly hazardous smoke event that impacted our study area on September 12–14, 2020. We did not observe linear effects of daily PM2.5 on average or peak daily values of acoustic indices; however, we did observe a significant reduction in ACI and BI during the three-day smoke event in 2020 and in the two weeks following this air pollution episode. Our results indicate that, on average, ACI and BI were reduced by 2.7 % and 15.9 % during and 1.5 % and 11.0 % afterward, respectively. These findings add further evidence that wildfire smoke alters soundscapes, likely due to changes in the presence, abundance, or behavior of acoustically active animals. Furthermore, our study demonstrates that wildfire smoke may have delayed and/or cumulative effects on acoustically active wildlife. Our study highlights the potential for passive acoustic monitoring to document wildlife responses to smoke pollution and identify potentially relevant exposure periods.

Soundscape characteristics of RAS tanks holding Atlantic salmon (Salmo salar) during feeding and feed withdrawal

Behavioural monitoring can provide crucial information on welfare and feeding in aquaculture. Passive acoustic monitoring of behaviour can be particularly useful in recirculating aquaculture systems (RAS), as they often have turbid water that impairs visual monitoring. Currently, little is known about the sounds that make up the soundscapes in RAS tanks holding Atlantic salmon (Salmo salar). In this study, hydrophones were used to continuously record the soundscape in eight single tank RAS holding Atlantic salmon parr for 15 days, with the fish in four of the tanks being fasted by feed withdrawal for five days from the sixth to the tenth day. The results show that soundscapes in RAS tanks are affected by feeding. Two main sound sources were identified during feeding in RAS tanks, one related to pellets delivery and the other to fish behaviour. The sound of pellets hitting the water surface had energy concentrated at frequencies between 1.7 and 4.0 kHz, with peak frequency decreasing and amplitude increasing with increasing number of pellets hitting simultaneously. The feeding sounds of Atlantic salmon had energy concentrated at frequencies between 6.5 and 9.4 kHz.More complex soundscapes were recorded during feeding events. These were characterized by variations in amplitude and frequency that have been described by using acoustic indexes in RAS tanks for the very first time. The Acoustic Complexity Index (ACI), the Acoustic Entropy Index (H) and the Normalized Difference Soundscape Index (NDSI) showed distinct changes in the soundscape related to feeding events; ACI increased while H and NDSI decreased compared to the times in between scheduled feeding times. The sound types identified in this study and the outcomes of the acoustic indices indicate a possibility to monitor system performance as well as fish behaviour in the tank soundscapes in RAS. Soundscape monitoring can contribute to match feeding closer to fish appetite, improve water quality, and reduce risks that deviations in the system performance can have on fish welfare during production.

Measuring biodiversity with sound: How effective are acoustic indices for quantifying biodiversity in a tropical dry forest?

AbstractLarge‐scale biodiversity conservation and management necessitate rapid assessment tools and technologies. Indices derived from passive acoustic data offer a novel solution for rapid biodiversity monitoring. Although these indices quantify vocalizing biodiversity at a site, previous studies indicate inconsistencies in the indices' performance across different biomes. We tested the efficacy of seven acoustic indices—acoustic complexity index, acoustic diversity index, bioacoustic index (BI), acoustic entropy index, total entropy (H), normalized difference soundscape index, and number of peaks in an understudied biome, tropical dry forests, in central India. We measured the relationship between every index and a combination of these indices with a biodiversity metric, avian species richness. We found a weak correlation between individual indices and species richness (0.00 ≤ R ≤ 0.35), while a combination of indices was comparatively better at predicting species richness (R2 = 0.54). Although BI performed better than all other indices, our results indicate that acoustic indices do not accurately quantify avian species richness in this forest in central India. However, combining multiple indices increases their efficacy, limitedly. We recommend evaluating the efficiency of acoustic indices, especially in underrepresented habitats, before their application in avifauna‐based rapid acoustic surveys.

Springtime spatio-temporal distribution of bird diversity in urban parks based on acoustic indices

Human-dominated urban ecosystems have encroached on native habitats, positioning urban parks as crucial sanctuaries that support bird diversity conservation. Bird communities tend to act as significant indicators of habitat quality. Birds play a key role in generating soundscapes in urban environments, where a healthy acoustic environment is essential not only for human well-being but also serves as a core focus for environmental monitoring and landscape enhancement. Previous studies have pointed out that acoustic indices have great advantages and strong feasibility for long-term environmental monitoring. However, few studies on the comparative analysis of bird diversity across urban parks subject to varying degrees of urbanization have been published in this field. In this study we recorded the springtime soundscape across 8 urban parks in Nanjing (China) from March to April 2023 for 10 hours each day. Six acoustic indices of Acoustic Complexity Index, Acoustic Diversity Index, Normalized Difference Soundscape Index, Bioacoustic Index, Acoustic Entropy Index and Power Spectral Density were used to quantify the monitoring results. To investigate the influence of vegetation habitats on bird activity, we utilized K-means clustering analysis to categorize the parks based on their developmental gradient, while Principal Component Analysis (PCA) was employed to simplify the dimensions of 12 vegetation factors. The results revealed that the distribution of birds in urban parks is a complex interplay of variables including the gradient of urban development, the functions of park plots, and the characteristics of vegetation habitats, among others. Day-to-day, human and bird activities show similarities, yet birds' responses to urban environments vary by location. The daily movement of visitors exerts a discernible influence on park birds, even those adapted to urban life. In instances of heightened human activity, birds demonstrate a proclivity for seeking refuge in less disturbed areas, and their activity space tends to be concentrated on higher plants. Vegetation communities in areas of high human disturbance are found to provide substantial support to bird habitats. Specifically, vegetation communities featuring tall trees or ground cover that form buffer zones have a significant positive effect on weakening the impact of human activities on bird communities. In terms of monitoring bird diversity with acoustic indices, Bioacoustic Index and Acoustic Diversity Index show more consistent performance, rendering them more reliable than other acoustic indices.

Unveiling nature’s beat: analyzing the acoustics of an aquatic bug in relation to urban sounds

Anthropophony is a prominent component of soundscapes worldwide and is known to impact biota. While responses to anthropophony in terrestrial and marine animals have been relatively well-studied, there is still a lack of knowledge regarding freshwater animals. In fact, freshwater taxa are among the possibly most threatened groups, and unveiling the reasons for their threat is crucial. We investigated the effect of low-frequency sounds -usually associated with anthropophony- on the stridulation of Krizousacorixa femorata, a common water bug in Mexico City. Using aerial recordings, we estimated the Normalized Difference Soundscape Index (NDSI), which is the most commonly used index to measure anthropophony, to characterize soundscapes in six city sites throughout the year. Additionally, from underwater recordings in the same sites, we obtained the peak frequency (Pf) of the stridulations, as it is the frequency with the highest energy and, therefore, the one that can travel the farthest and can be identified even in the presence of overlapping sounds. Finally, we evaluated the relationships between soundscapes and Pf through a mixed linear model. There was a negative correlation between NDSI and Pf, indicating higher-pitched stridulations at sites with dominant anthropophony. While we cannot rule out other factors contributing to stridulation variation, we remain uncertain about how low-frequency sounds impact freshwater ecosystems and the intricate relationship between soundscapes and aquatic life in urban settings.

An exploratory framework for mapping, mechanism, and management of urban soundscape quality: From quietness to naturalness

BackgroundDespite growing attention from researchers and governments, challenges persist in comprehensively assessing urban sound quality by integrating both quietness and naturalness aspects. GoalsThis study aimed to develop an innovative soundscape quality index that concurrently evaluates quietness and naturalness in urban soundscapes. Our objectives included conducting urban soundscape quality mapping, analyzing influential mechanisms, and identifying priority zones for sound environment management. ApproachesWe collected sound pressure level (SPL) and raw audio data, from which we computed a normalized difference soundscape index (NDSI). With a dataset comprising 28 explanatory variables encompassing land use, built environment, vegetation characteristics, and temporal factors, we employed the random forest (RF) model to predict 10 indicators, including eight SPL-related indices, NDSI, and the QNS (quietness and naturalness soundscape) index. Crucially, we utilized SHAP (SHapley Additive exPlanations) values to interpret the RF model. FindingsSpatial variations in quietness and naturalness were evident, closely associated with road networks and vegetation, respectively, with discernible temporal variations. The top three variables influencing QNS were distance to major roads, normalized difference vegetation index (NDVI), and proportion of tree coverage. Moreover, interaction effects highlighted dual negative or synergistic promoting effects on QNS from factors such as road width, human disturbance, vegetation configurations, and land cover. Notably, these mechanisms were successfully applied to six typical tourist attractions in Xiamen city, where five types of management zones were mapped based on priority considerations of population density and soundscape quality. Interestingly, natural soundscape reserves were highly correlated with city parks, high-risk zones predominantly overlapped with road networks, and potential zones comprised inner communities between streets. SignificanceThe framework demonstrated effectiveness in mapping, exploring mechanisms, and guiding management strategies for the urban sound environment.

Landscape and soundscape quality promote stress recovery in nearby urban nature: A multisensory field experiment

Cities have different benefits and risks, but are often stressful environments to live in. Everyday contact with nearby nature can be a crucial way to alleviate stress and increase the well-being of citizens. However, there is still limited evidence on how nature-health benefits vary according to the type and quality of natural environments. This study integrated multiple landscape and soundscape objective and perceived assessments to examine stress recovery in different types of neighbourhood nature. We used a field randomised experiment (n=45) to analyse effects of various random and fixed factors on restoration including: environmental conditions (e.g. temperature, wind, air quality), personal characteristics (e.g. age, gender, perceived health, nature connectedness), presence of other people and environmental quality (e.g. Perceived Environmental Aesthetic Qualities Scale and Perceived Sound Affective Quality scale). We found that physiological and psychological restoration is significantly greater in sites with higher visual (% visual natural elements) and acoustic (Normalized Difference Soundscape Index (NDSI)) naturalness i.e. the beach and forest, compared to the urban park (control site). Perceived landscape and soundscape quality were strongly associated with stress recovery, and these results were more pronounced for the soundscape. This highlights that soundscape quality assessments deserve more systematic attention in urban green infrastructure research and planning. Finally, we found important early evidence of reduction in Electrodermal activity (EDA) only within 3 minutes of nature exposure especially in the forest.

Recognition of bird species with birdsong records using machine learning methods.

The recognition of bird species through the analysis of their vocalizations is a crucial aspect of wildlife conservation and biodiversity monitoring. In this study, the acoustic features of Certhia americana, Certhia brachydactyla, and Certhia familiaris were calculated including the Acoustic complexity index (ACI), Acoustic diversity index (ADI), Acoustic evenness index (AEI), Bioacoustic index (BI), Median of the amplitude envelop (MA), and Normalized Difference Soundscape Index (NDSI). Three machine learning models, Random Forest (RF), Support Vector Machine (SVM), and Extreme Gradient Boosting (XGBoost), were constructed. The results showed that the XGBoost model had the best performance among the three models, with the highest accuracy (0.8365) and the highest AUC (0.8871). This suggests that XGBoost is an effective tool for bird species recognition based on acoustic indices. The study provides a new approach to bird species recognition that utilizes sound data and acoustic characteristics.

Passive acoustic monitoring as a way to assess daily dynamics of animal activity in urban green areas

Fast process of urbanization makes it crucial to include cities in assessment of all global processes. Urban areas on the one hand are subjects to the high levels of anthropogenic influence. On the other hand, urban green areas could provide shelter for some species, inhabiting highly disturbed rural landscapes. The data on daily dynamics of activity is required to assess the impact of noise and light pollution on biodiversity. In this study we have checked the efficiency of passive acoustic monitoring (PAM) in assessing the daily dynamics of animal acoustic activity in city parks. We have identified the acoustic signals of birds on the records and calculated the time of each species acoustic activity. Moreover, we have conducted the classical birds’ survey to assess the efficiency of PAM. In order to evaluate the possibility of using acoustic indices to assess daily dynamics of acoustic activity, we have calculated NDSI, BI, ACI and ADI indices for each hour a day. We managed to acoustically detect 70% of species, found by route census by single recorder. NDSI (Normal Difference Soundscape Index) correlates well with total acoustic activity of animals and could be used as indicator for this parameter.

Assessing the effect of zoo closure on the soundscape using multiple acoustic indicators

The zoo soundscape has important implications for animal welfare, management, and conservation. However, despite its importance, the zoo soundscape is yet to be examined in depth. Consistent human presence can influence the zoo soundscape. However, it is difficult to determine the specific impact of human presence, as visitors are usually present during the day when animals are active. The COVID-19 lockdown in 2020 provided a unique opportunity to study zoo soundscapes in the absence of visitors. The main aim of this study was to compare the sound environment across three zoo aviaries during the 2020 closure period to a comparable period in 2019 in which the zoo was open. We examined broad band frequency measures of sound pressure levels, sound pressure levels in defined frequency bands, and ecoacoustic indices (the Acoustic Complexity Index and Normalized Difference Soundscape Index) to describe the zoo soundscape. Ecoacoustic indices have not, to our knowledge, previously been used in the zoo setting, although they may provide a useful metric to assess zoo soundscapes. Therefore, we used this natural experiment to explore how successful these measures may be in assessing sound in zoo environments. We found that, during the zoo closure period, the overall sound pressure levels were lower (by 4.4 – 6.4 dB(Z) depending on aviary), and this effect was particularly pronounced in the lower frequency bands. The proportion of sound energy at low frequencies was also lower during the zoo closure period in two of the three aviaries. We argue that NDSI could be a useful index for determining the impact of human presence in zoos, although further information on how it is influenced by additional factors, such as human speech, would be beneficial. The use of multiple indices to assess the sound environment can provide additional information beyond traditional measures of sound levels in zoos, such as frequencies where sound energy is concentrated and characteristics of the soundscape, which could be used to better target management and mitigation.

The soundscape method and eco-acoustic indicators in the analysis of the acoustic environment of the mountain national parks in Poland and Sweden

Soundscape is one of the essential environmental elements affecting people’s experience in nature spaces. In the complex mechanism of landscape and soundscape perception, the acoustic characteristics of the environment are the primary influencing factor. The aim of the paper is the analysis of soundscape of two mountain national parks—Tatra National Park (TNP) in Poland and Sarek National Park (SNP) in Sweden. The first park is very frequently visited by tourists (around 4 million tourists a year) while the second park has an attendance of around a few thousand tourists. The paper presents the results of the analysis of acoustic measurements and ambisonic recordings made in the Koscieliska Valley (TNP) and the Rapa Valey (SNP, Swedish: Rapadalen) using classical method and the soundscape method. In addition, psychoacoustic parameters and soundecology indicators such as loudness, sharpness or roughness, ACI (acoustic complexity index), NDSI (normalized difference soundscape index), BIO (bioacoustic index), ADI (acoustic diversity index), and AEI (acoustic evenness index) were calculated.

Effect of an Artificial Sound-Based Index on the Perception of Historical Block Environments

The acoustic environment can influence people’s perceptions and experiences and shape the soundscape. The soundscape has a unique role in shaping the cultural identity of a regional culture. Artificial sounds are an essential source of sounds in historical blocks; research has shown the influence of the ratio of perceived artificial sounds to the perceived extent of natural sounds on environmental perception in historical blocks. In order to explore this impact, this study uses the red soundscape index (RSIn), which represents the ratio of perceived artificial sounds to natural sounds, and constructs a structural equation model to elucidate the relationship between RSIn, soundscape perception, and sense of place. The results show that: (1) The evaluation of the sense of place is inversely related to the perception of artificial sounds and positively related to the perception of natural sounds. (2) Different artificial sounds have different effects on soundscape perception and the sense of place; the traditional culture soundscape index (TRSIn) has a significant impact on soundscape pleasantness (β = −0.13, p < 0.001) and soundscape quality (β = −0.09, p < 0.01). (3) The human soundscape index (ARSIn) has a significant impact on the sense of place (β = −0.14, p < 0.001). (4) The music soundscape index (MRSIn) has a significant negative impact on soundscape quality (β = −0.13, p < 0.05) and the sense of place (β = −0.12, p < 0.05). Therefore, the different dominant artificial sound sources should be considered and emphasized when designing and optimizing the soundscape of historic districts. The results of this study can serve as design guidelines and supporting data, providing a reference for the optimization and enhancement of the soundscape of historical blocks.

Can acoustic indices reflect the characteristics of public recreational behavioral in urban green spaces?

Acoustic indicators serve as an effective means of assessing the quality of urban green space soundscape. The informative, easy accessibility and non-invasive nature of acoustic monitoring renders it an excellent tool for studying the interaction among the natural environment, wildlife, and human activities. Urban green space is essential in the urban ecosystem and constitutes the primary location for public outdoor recreation. However, the existing methods for monitoring public recreational behavior, such as on-site observation, drone observation, or questionnaire interviews, require significant labor or professional expertise. All of these methods have their limitations, so there is still much to be researched in the acoustic indices and recreational behavior. As a result, the potential for using acoustic characteristics to monitor public recreational behavior remains underexplored. To address this gap, this study investigates the potential of 5 widely used acoustic indices and acoustic intensity for monitoring public recreational behavior: Acoustic Complexity Index (ACI), Acoustic Diversity Index (ADI), Acoustic Richness (AR), Normalized Difference Soundscape Index (NDSI), and Power Spectral Density (PSD). Data were collected from 35 monitoring points in urban green spaces during the opening hours (6:00–22:00) to analyze the relationship between these indices and public recreational behavior. The findings indicate that (1) ACI, ADI, and AR daily exhibited multi-peak daily variation characteristics similar to those of public recreational behavior, displaying a “W” shape, while NDSI exhibits opposite variation characteristics; (2) the spatial variation characteristics of ACI, ADI, and AR change in response to the green space, and these changes align with public recreational behavior; (3) the correlation analysis and generalized linear mixed model construction further demonstrate that acoustic indices are effective in capturing the dynamic activities of visitor behavior; and (4) PSD undergoes significant temporal dynamic changes along the frequency gradient, with different frequency intervals reflecting the activity information of different recreational behaviors. In conclusion, this research highlights the effectiveness of using acoustic indices to analyze both the spatial and temporal variation characteristics of public recreational behavior in urban green spaces. The results can provide valuable data support for the enhancement and renovation of urban green spaces.

Investigating the effects of tree species diversity and relative density on bird species richness with acoustic indices

Mixed-species forest stands may provide suitable habitats for more bird species than tree monocultures by increasing the number of niches and resources available. However, assessing the effects of forest diversity on birds over time and across multiple sites using traditional bird survey methods can be expensive, time-consuming and impractical. Alternatively, we used passive acoustic monitoring (PAM) and acoustic indices to investigate how tree species diversity, relative density, and other plot characteristics affect the species richness of avian communities in temperate forests. Acoustic monitoring was conducted in Nationalpark Hainich, Germany, using plots which differed in tree species diversity and relative species density. Using a subset of our data, five acoustic indices, the normalised difference soundscape index (NDSI), acoustic complexity index (ACI), bioacoustic index (BI), the acoustic evenness index (AEI) and temporal entropy (Ht), were initially assessed using audio recordings of different soundscape elements to determine the degree to which they were influenced by non-biophony soundscape elements. Of these, NDSI, ACI and BI were considered least biased and displayed significant positive relationships with bird species richness assessed using audio recordings. However, NDSI values plateaued at around 5 bird species when measuring bird species richness and ACI values for dawn choruses were lower than expected, potentially due to the high density of birdsong saturating the soundscape. Plot tree species diversity had significant positive effects on ACI and BI during dawn, dusk and daytime periods. Increased basal area of sycamore (Acer pseudoplatanus) and, to a lesser degree, beech (Fagus sylvatica), had a negative effect on acoustic indices. These results could potentially be due to the earlier leaf out timings of these tree species in relation to the dates when surveys were performed. While the use of PAM and acoustic indices enabled surveys across multiple sites over longer time periods than would previously have been achievable, our results show that care should be taken when selecting indices and interpreting acoustic index results.

The sound of restored soil: using ecoacoustics to measure soil biodiversity in a temperate forest restoration context

Forest restoration requires monitoring to assess above‐ and belowground communities, which is challenging due to practical and resource limitations. Ecological acoustic survey methods––also known as “ecoacoustics”––are increasingly available and provide a rapid, effective, and non‐intrusive means of monitoring biodiversity. Aboveground ecoacoustics is widespread, but soil ecoacoustics has yet to be utilized in restoration despite its demonstrable effectiveness at detecting soniferous soil meso‐ and macrofauna. This study applied ecoacoustic tools and indices (Acoustic Complexity Index, Normalized Difference Soundscape Index, and Bioacoustic Index) to measure belowground (and aboveground as secondary) biodiversity in a forest restoration site spanning two age classes. We collected n = 198 belowground acoustic samples and n = 180 aboveground samples from three recently deforested (felled <3 years ago) and three deciduous forest plots undergoing restoration (for the last 30–51 years) across three monthly visits in South Yorkshire, U.K. We used a belowground sampling device and sound‐attenuation chamber to record soil communities and passive acoustic monitoring to record aboveground sounds. We found that restored plot acoustic complexity and diversity were significantly higher than deforested plots in the sound‐attenuation chamber, but there were no inter‐plot differences in in‐situ soil or aboveground samples. We also found that restored plots had a significantly greater high‐frequency to low‐frequency ratio (suggesting higher biophony to anthrophony ratios) for in‐situ and sound chamber soil but no association for aboveground samples. Our results suggest that ecoacoustics has immense potential to monitor belowground biodiversity, adding to the restoration ecologist's toolkit and supporting global ecosystem recovery.

Free-ranging livestock changes the acoustic properties of summer soundscapes in a Northeast Asian temperate forest

If not properly managed, free-range livestock grazing could be a great threat to forest ecosystems by causing heterogeneous and unpredictable changes in forest structure, functions, and biodiversity. Understanding these changes is important for informing land management decisions compatible with long-term biodiversity conservation. Passive acoustic monitoring (PAM) of biodiversity may provide integrative indices for assessing grazing effects. However, little is known about the responses of soundscape characteristics to forest grazing, especially in temperate forests. Here, we use bioacoustics to assess the impact of continuous livestock grazing on acoustic indices at the landscape scale in Northeast China. We compared the acoustic complex index (ACI), acoustic diversity index (ADI), acoustic evenness index (AEI), bioacoustic index (BIO), total acoustic entropy (H), and normalized difference soundscape index (NDSI) between 16 cattle-grazed forest plots and 36 ungrazed forest plots for different time scales (24 h diel cycles, dawn, day, dusk and night). We collected and analysed over 7000 h of recordings from 52 sites. Our results showed that the six acoustic indices exhibited distinct diel patterns in both forest habitats. Moreover, several indices, except for the ADI and AEI, significantly responded to grazing over 24 h diel cycles, but with contrasting patterns; compared to grazed forests, ungrazed forests had much more bioacoustics activity measured by significantly higher ACI and NDSI values and significantly lower BIO and H values. Livestock grazing was a key driver of diel acoustic patterns, resulting in the loss of nocturnal and dawn soundscapes. Our results indicate that intensive/excessive livestock grazing has a significant negative impact on soundscape quality in human-dominated temperate forest areas, which is likely triggered by shifts in faunal assemblages. Livestock, for example, may reduce the occupancy of sika deer (Cervus nippon), resulting in fewer sika deer vocalizations in grazed forests. Cattle lowing and the intensive sounds of cattle bells may also mask biological vocalizations. We argue that multiple acoustic indices are required to adequately account for the complex responses of soundscapes to large-scale livestock grazing. For forest management, we propose employing PAM to quantify the acoustic communities of the landscape from a new perspective, thereby fostering evidence-based forest management at the local scale to reconcile the livestock sector with ecosystem conservation.