Acoustics Community Research Articles

Structure and dynamics of mixed‐species choruses in a tropical anuran assemblage: insights from network analysis

AbstractMales of a wide variety of vertebrates aggregate in mixed‐species choruses to attract females and signal territory occupancy. It is often assumed that species within these choruses co‐signal, interact and compete for the acoustic space, although few studies have tested this assumption, particularly in tropical and highly diverse environments. Using a novel combination of passive acoustics and network analysis, we monitored calling activity of a tropical anuran assemblage for an entire year and examined the structure and dynamics of mixed‐species choruses. Species composition was determined at 1‐min resolution on 288 recording hours and then used to estimate a set of centrality metrics (degree, strength and eigenvector) that characterize the species roles within the acoustic network. The studied assemblage formed a dynamic network comprising eight species during the rainy season and four during the dry season. These species showed distinct roles within the network, ranging from central species (those co‐signalling frequently and with many species) to peripheral species (those barely co‐signalling and with few species). Our results shed light on the species interactions in acoustic communities and challenge the general assumption of an equal contribution of species to the mixed‐species choruses. While in the rainy season the territorial frogs Boana albopunctata and B. faber exhibit the most prominent role within the network (with a higher degree, strength and eigenvector centrality), all of the species calling in the dry season co‐signalled with equal number of species, with only another territorial species, B. lundii, showing a higher rate of co‐signalling events (higher strength and eigenvector centrality). This suggests that territorial behaviour may favour increased calling activity and hence central roles in acoustic networks. These findings contribute to a better understanding of chorus dynamics in tropical assemblages and have crucial implications for the study of species interactions and the evolutionary hypotheses of acoustic divergence.

Convergent acoustic community structure in South Asian dry and wet grassland birds.

ABSTRACTAlthough the study of bird acoustic communities has great potential in long-term monitoring and conservation, their assembly and dynamics remain poorly understood. Grassland habitats in South Asia comprise distinct biomes with unique avifauna, presenting an opportunity to address how community-level patterns in acoustic signal space arise. Similarity in signal space of different grassland bird assemblages may result from phylogenetic similarity, or because different bird groups partition the acoustic resource, resulting in convergent distributions in signal space. Here, we quantify the composition, signal space and phylogenetic diversity of bird acoustic communities from dry semiarid grasslands of northwest India and wet floodplain grasslands of northeast India, two major South Asian grassland biomes. We find that acoustic communities occupying these distinct biomes exhibit convergent, overdispersed distributions in signal space. However, dry grasslands exhibit higher phylogenetic diversity, and the two communities are not phylogenetically similar. The Sylvioidea encompasses half the species in the wet grassland acoustic community, with an expanded signal space compared to the dry grasslands. We therefore hypothesize that different clades colonizing grasslands partition the acoustic resource, resulting in convergent community structure across biomes. Many of these birds are threatened, and acoustic monitoring will support conservation measures in these imperiled, poorly-studied habitats. This article has an associated First Person interview with the first author of the paper.

First person – Sutirtha Lahiri

ABSTRACTFirst Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Sutirtha Lahiri is first author on ‘Convergent acoustic community structure in South Asian dry and wet grassland birds’, published in BiO. Sutirtha is a research assistant in the lab of Dr Anand Krishnan at the Indian Institute of Science Education and Research (IISER) Pune, India, investigating whether biogeographically distinct grasslands display convergent acoustic community structure.

What does resilience sound like? Coral reef and dry forest acoustic communities respond differently to Hurricane Maria

Disturbance regimes and biodiversity—two factors that govern the stability of ecosystems—are changing rapidly due to anthropogenic forces including climate change. Determining whether ecosystems retain their structure and function through intensifying disturbance regimes is an urgent task. However, quantitatively assessing the resilience of natural systems is a complex and challenging endeavor, especially for animal communities, for which datasets around disturbance events are scarce. Here, we apply an emerging remote sensing technology—the recording and analysis of soundscapes—to quantify the resilience of Puerto Rican coral reef and dry forest animal communities in relation to Hurricane Maria, which struck the island in September 2017. Using recordings collected between March 2017 and January 2018 at three terrestrial and three marine sites, we measured three dimensions of resilience—the magnitude of the impacts (resistance), the spatial pattern of the impacts (heterogeneity), and the diversity and timeline of functional responses (recovery)—across eight sound types representing different broad taxonomic groups. While the coral reef communities exhibited high resistance to the storm, all sound types within the dry forest were significantly impacted, with two of the three insect choruses and bird vocalizations at dawn declining approximately 50% in the weeks following Hurricane Maria. The mid-frequency insect sound type returned to pre-storm levels after 56 days, while bird vocalizations returned after 67 days, though seasonal and lunar patterns underscored the importance of long-term data for accurately measuring trajectories of recovery. This study demonstrates that soundscape methodologies can help to quantify elusive dimensions of animal community resilience in order to better understand how biodiversity and ecosystem functioning will change under novel disturbance regimes.

The quiet project-UK acoustic community’s response to COVID-19

The COVID-19 Lockdown created a new kind of environment both in the UK and globally, never experienced before or likely to occur again. A vital and time-critical working group was formed with the aim of gathering crowd-source high quality baseline noise levels and other supporting information across the UK during the lockdown and subsequent recovery period. The acoustic community were mobilised through existing networks engaging private companies, public organisations, and academics to gather data in accessible places. A website was designed and developed to advertise the project, provide instructions and to formalise the uploading of noise data, observations, and Soundscape feedback. In addition, pre-existing on-going measurements from major infrastructure projects, airport, and planning applications were gathered to create a data repository of 1.6 GB. The plan was to have regular 6 monthly national noise surveys, which turned into multiple Lockdown surveys. Noise data has been compared to the traffic flow data from the TRIS national wide permanent monitoring system. Ultimately, the databank will be used to establish the relation to other impacts such as air quality, air traffic, economic, and health and wellbeing. As publicly funded research the databank will be made publicly available to assist future research.

Broadband global acoustic cloaking experiments

Rendering objects invisible to impinging acoustic waves (i.e., acoustic cloaking), is a mature topic in the acoustic community and has diverse applications. Nevertheless, existing approaches and physical demonstrations still exhibit a large range of assumptions and limitations. Passive approaches, which surround the scattering object with a suitable (meta-)material, are usually only effective in a narrow frequency-band and cannot adapt to changing incident fields. Active approaches, which rely on the emission of a secondary wavefield that destructively interferes with the scattered field, have the potential to respond dynamically and be broad band. However, without knowledge of the primary or scattered field, the signals for the secondary sources need to be estimated from wavefield measurements in real-time. To our knowledge, this was never demonstrated beyond 1D acoustic experiments to achieve global broadband control of forward- and backscattered waves. Here, we present experimental results of active, broadband 2D acoustic cloaking without any assumptions of the primary or scattered wavefields. Using a low-latency control system and a dense array of control microphones, the signals for 20 control sources surrounding the scatterer are estimated and applied in real-time to achieve fully deterministic, global acoustic cloaking.

Atlantic deepwater ecosystem observatory network: Patterns of acoustic backscatter and community structure of the U.S. Outer Continental Shelf

Three nodes in the Atlantic Deepwater Ecosystem Observatory Network (ADEON) network on the U.S. Mid- and South Atlantic Outer Continental Shelf (OCS) contain an upward looking, multi-frequency echosounder system. Data was collected from November 2017–December 2020 at these sites extending from the OCS waters of Virginia down to Florida. Along shelf backscatter comparisons were made for general scattering groups related to fish and zooplankton across time and latitude. Unique seasonal patterns were observed across sites both in terms of volume backscatter magnitude and community structure. Measurements made within this research program will serve as a baseline for pattern and trend analyses of acoustic backscatter related to ecosystem components of this traditionally under sampled, offshore region. Study concept, oversight, and funding were provided by BOEM under Contract No. M16PC00003, in partnership with ONR and NOAA. Funding for ship time was provided under separate contracts by ONR, Code 32.

Ecoacoustics and Multispecies Semiosis: Naming, Semantics, Semiotic Characteristics, and Competencies

Biosemiotics to date has focused on the exchange of signals between organisms, in line with bioacoustics; consideration of the wider acoustic environment as a semiotic medium is under-developed. The nascent discipline of ecoacoustics, that investigates the role of environmental sound in ecological processes and dynamics, fills this gap. In this paper we introduce key ecoacoustic terminology and concepts in order to highlight the value of ecoacoustics as a discipline in which to conceptualise and study intra- and interspecies semiosis. We stress the inherently subjective nature of all sensory scapes (vivo-, land-, vibro- and soundscapes) and propose that they should always bear an organismic attribution. Key terms to describe the sources (geophony, biophony, anthropophony, technophony) and scales (sonotopes, soundtopes, sonotones) of soundscapes are described. We introduce epithets for soundscapes to point to the degree to which the global environment is implicated in semiosis (latent, sensed and interpreted soundscapes); terms for describing key ecological structures and processes (acoustic community, acoustic habitat, ecoacoustic events) and examples of ecoacoustic events (choruses and noise) are described. The acoustic eco-field is recognized as the semiotic model that enables soniferous species to intercept core resources like food, safety and roosting places. We note that whilst ecoacoustics to date has focused on the critical task of the development of metrics for application in conservation and biodiversity assessment, these can be enriched by advancing conceptual and theoretical foundations. Finally, the mutual value of integrating ecoacoustic and biosemiotics perspectives is considered.

Vegetation, bird and soundscape characterization: a case study in Braulio Carrillo National Park, Costa Rica

We assessed the structural complexity of vegetation, birds and soundscapes in two areas of Braulio Carrillo National Park, Costa Rica, with different road exposure, as baseline information for conservation and management. We measured vegetation structure complexity, surveyed birds and recorded soundscapes in an area adjacent to the National Highway 32 (Quebrada) and another area 20 km away (Ceibo). Quebrada presented a more open forest structure and lower density of trees and shrubs; lower evenness and higher acoustic complexity, higher bioacoustic activity and sound pressure level; higher bird abundance and richness. Ceibo showed a higher density of trees and shrubs, higher complexity of vegetation structure, higher proportion of biophonies than anthrophonies, and an acoustic community with higher diversity and entropy. The study sites differed in characteristics of their bird communities in an unexpected way; these differences appear to be mostly influenced by the structure and complexity of the vegetation surrounding the road. However, the soundscapes seemed to properly reflect the habitat condition, and are promising for evaluating the ecological condition of a site.

It is not just about birds: what do acoustic indices reveal about a Costa Rican tropical rainforest?

ABSTRACT Acoustic monitoring is used to assess biodiversity across large spatial and temporal scales. However, extracting meaningful information from large data sets might be exceedingly time consuming. For this reason, acoustic indices have been proposed as proxies for biodiversity monitoring. Although acoustic indices hold great promise for standardizing acoustic data analysis, the complexity of acoustic conditions requires careful examination of the relationship between an index and the underlying process of interest. We evaluated 11 acoustic indices at two operational levels: (1) acoustic community level (an aggregation of species that produces sound), using birds as an example to assess how well acoustic indices predict bird indices (abundance, richness, evenness and diversity); and (2) soundscape level (the collection of biological, geophysical and anthropogenic sounds from a landscape), using acoustic indices to classify the study sites according to their ecological condition. To study the relationship among these variables, we selected two study sites with different ecological conditions (in terms of vegetation structure and traffic noise) within the Braulio Carrillo National Park (BCNP), Costa Rica. We sampled the soundscape and bird community using 12 sampling points and four visits to each study site from June 2017 to August 2018. We continuously recorded sounds at sunrise and sunset, and for 10 minutes every hour, during two consecutive days per visit. In addition, we performed four bird counts per visit (sunrise and sunset). We performed a correlation analysis between 11 acoustic indices and 4 community bird indices. We analyzed the ability of acoustic indices to predict bird indices. Furthermore, we used acoustic indices to classify the two sites according to their ecological condition. Bird abundance and richness were positively correlated with acoustic evenness indices and negatively correlated with the acoustic diversity index, but the whole set of acoustic indices predicted bird indices weakly. However, the classification of the sites using acoustic indices was conducted with a high average precision of 0.93 (sd = 0.08). Acoustic indices appear to be more promising for evaluating the ecological condition of a site than abundance, richness or diversity of specific animal groups, in this case birds, in tropical rainforests.

The Quiet Project – UK Acoustic Community’s response to COVID19 during the easing of lockdown

Abstract The COVID-19 lockdown created a new kind of environment both in the UK and globally, never experienced before or likely to occur again. A vital and time-critical working group was formed with the aim of gathering crowd-source high quality baseline noise levels and other supporting information across the UK during the lock-down and subsequent periods. The acoustic community were mobilised through existing networks engaging private companies, public organisations and academics to gather data in accessible places. In addition, pre-existing on-going measurements from major infrastructure projects, airport, and planning applications were gathered to create the largest possible databank. A website was designed and developed to advertise the project, provide instructions and to formalise the uploading of noise data, observations and soundscape feedback. Two case studies gathered in the latter stage of full lockdown are presented in the paper to illustrate the changes in the environmental noise conditions relative to transport activity. Ultimately the databank will be used to establish the relation to other impacts such as air quality, air traffic, economic, and health and wellbeing. As publicly funded research the databank will be made publicly available to assist future research.

城市公园春季声景观与植被结构的关系

城市公园是城市生态系统的重要组成部分和城市生物多样性热点地区，具有丰富的声景观资源。由于声景观及声学方法具有信息量大，成本低，低侵入的特点，因此其研究和应用对生态系统健康及监测具有较高价值。声景观研究通过总结生物声的活动或多样性来衡量生物多样性。记录了北京20个城市公园的春季声景观，使用定量方法描述了声景观特征与变化；测试三种了已被证明与生物多样性相关并被广泛使用的声学指数（BIO、ADI、NDSI）与植被群落关系，完成了城市环境中声景观与环境关系的初步探究。研究结果表明：（1）声学指数能够有效表征城市公园声景观信息，具有显著的时间动态特性，能准确反映鸟类黎明合唱等重要生物生态活动；（2）声学强度指数也具有显著的时间动态变化和沿频率梯度的变化，不同的频率区间反映了不同声学群落的活动信息；（3）植被结构尤其是垂直结构对声景观起着重要作用，垂直异质性越大，声学多样性越高。发现支持声景观作为公园植被状况的度量，强调了其作为生物多样性和生态系统健康状况监测方法，用于城市管理和可持续发展的巨大潜力。;Urban foresters are addressing the challenges of urban biodiversity loss through management plans to adapt to urbanization. Protecting the integrity of the urban ecosystem requires long-term monitoring and planning for resilience as well as effective management. Urban parks are important parts of the urban ecosystem and hot spots of urban biodiversity, with rich soundscape resources. Due to the informative, low-cost, and low-impact features, soundscape-related researches and applications have a great potential of monitoring ecosystem health. Acoustic indices have been commonly used in soundscape ecology researches to measure biodiversity conditions by summarizing the activity or diversity of biological sounds. In this study, we recorded the soundscapes of 20 city parks within Beijing urban area in spring, trying to describe the characteristics and changes of soundscape quantificationally. A total of 23,040 minutes of sound materials were automatically sampled from raw data using Python. Then we calculated three widely used acoustic indices (BIO, ADI, NDSI) that have been proven to be related to biodiversity. The soundscape intensity index, power spectral density (PSD), was calculated to measure acoustic features along every frequency interval. All the indices' calculation is based on R studio. Spearman rho correlation analysis and principal component analysis were carried out to explore how environmental vegetation structures affecting soundscape in park habitats. The results show that (1) acoustic indices can not only effectively characterize the soundscape information of urban parks, but also have significantly time-dynamic characteristics, which can accurately reflect important biological activities and ecological processes such as bird dawn chorus. (2) The acoustic intensity index also reflects significantly temporal variations and changes along the frequency intervals. Different frequency interval groups reflect the corresponding activity information of acoustic communities. These results also provide more supports to the acoustic niche hypothesis (ANH) theory. (3) Our PCA modelling results show that the vegetation structure, especially the vertical structure, plays an important role in urban soundscapes. More vertical heterogeneity or multilayered vegetation, is associated with more acoustic diversity in urban parks. In the absence of historical soundscape data, we systematically collected and analyzed the soundscape of urban parks in Beijing. This is a pilot study for soundscape in Beijing urban parks. Our findings support soundscape as a measurement of habitat vegetation status and emphasize its great potential for urban management and sustainable development in biodiversity and ecosystem monitoring, which will enable regular assessment of urban parks and forests to inform adaptive planning and management strategies.

Vegetation structure and temporality influence the dominance, diversity, and composition of forest acoustic communities

Bioacoustic methods analyze sounds to monitor wildlife in forests, providing novel perspectives to understand the relationship between forest vegetation structure and wildlife species. Bioacoustic studies differ from traditional field surveys that are often more visual and require work in the daytime. A sampling of acoustic signals is possible to explore the diurnal variation of the forest ecosystem. Normalized difference soundscape index (NDSI), acoustic diversity index (ADI), and power spectral density (PSD) were chosen as acoustic indices to quantify the dominance, diversity, and composition of the biophony of forest settings. Biophony was recorded in ten south subtropical evergreen broad-leaved forest sites in Shenzhen, China. Composition structure (species richness), horizontal structure (vegetation density and canopy cover), and vertical structure (tree height diversity and each layer height) were used to evaluate the structure of vegetation. Linear Mixed Models (LMMs) were applied to examine the effects of different vegetation structures on biophony between day and night. The relationships between various biophonic frequency bands and vegetation structural variables during day and night were estimated by redundancy analysis (RDA). Results showed that different sound frequencies and vocalization behavior of vocalizing species determine the variance between the forest sound environment during day and night. Forest canopy and understory have a significant influence on biophonic diversity and dominance separately. The vocalizing species' preferences for different habitats were affected by the same vegetation structure variables across diurnal variation. Canopy cover and understory species richness had a significant positive effect on low-frequency biophony, and tree height diversity was found to have a significant positive impact on high-frequency biophony. Finally, tree height diversity was the core variable in the forest acoustic environment, and higher tree height diversity resulted in a more dominant and diverse biophony. This study shows the potential of bioacoustic methods to reveal the day-night dynamics of vocalizing species, using easily measured acoustic variables that can help with the timely evaluation of potential impacts of vegetation structure on forest animal communities.

Graduate studies in acoustics and noise control in the School of Mechanical Engineering at Purdue University

The acoustics community at Purdue University will be described with special emphasis on the graduate program in Mechanical Engineering. Around 30 Purdue faculty study aspects of acoustics and closely related disciplines and so there are many classes to choose from as graduate students structure their plans of study to complement their research activities and to broaden their understanding of acoustics. In Mechanical Engineering, the primary emphasis is on understanding noise generation, noise propagation, and the impact of noise on people, as well as development of noise control strategies including active noise control, experimental techniques, and noise and noise impact prediction tools. The noise control research is conducted at the Ray W. Herrick Laboratories, which houses several large acoustics chambers that are designed to facilitate testing of a wide array mechanical systems, reflecting the Laboratories' long history of industry-relevant research. Complementing the noise control research, Purdue has vibrations, dynamics and electromechanical systems research programs and is home to a collaborative group of engineering and psychology professors who study human perception and its integration into engineering design. There are also very strong ties between ME acoustics faculty and faculty in Biomedical Engineering and Speech Language and Hearing Sciences.

Cognitive sampling: The power of harnessing sampling strategies with machine learning techniques for enhanced machine classification and machine interpretation of acoustic datasets

Machine learning has received increased popularity in the acoustical community for its ability to interpret, classify and predict information autonomously from large-scale datasets. Beyond traditional supervised and semi-supervised learning architectures such as deep learning, and ensemble approaches, unsupervised learning networks such as autoencoders are being used to discover efficient data codings that enable hitherto unforeseen feature spaces. Unrelated yet deeply significant to the success of these myriad approaches is the spectral resolution of the signal itself as it has implications on the richness of information used by the learning architecture. Furthermore, much remains to be done in interpreting machine-learnt feature representations by domain experts and linking the domain knowledge to the machine-learnt knowledge. This talk will introduce a new way of enabling this link, by harnessing the power of compressive sampling and more generally, non-uniform sampling strategies and information theory to popular machine learning techniques. Specific applications will include a variety of acoustical applications involving spectral feature generation and interpretation.

On the practical application of the impulse response measurement method with swept-sine signals in building acoustics.

Impulse response (IR) measurement methods with deterministic signals have been used in various fields of acoustics for decades, yet there is still a hesitancy to apply them by some practitioners, especially in the building acoustics community. This hesitancy is also the topic of discussion in ASTM standards committees because IR methods are not allowed in ASTM standards. The criticism that prevents a more widespread adoption is that the description of IR methods in existing standards such as ISO 18233 is not sufficient to enable practitioners and equipment manufacturers to reliably implement them. Previous publications have described the theoretical background well, but they have not given sufficient guidance for the practical application with respect to the parameters of the measurement signal. To provide more guidance and show the practical advantages of IR measurement methods, this paper investigates the effects of the design parameters of swept-sine signals. Measurements in a reverberant chamber are used to highlight potential problems and appropriate solutions derived from a theoretical background. Suggestions for the design of measurement signals and for the post-processing of the measured data are provided to achieve optimal and reliable results. This contribution hopefully gives practitioners more confidence in applying the method in the future.

Acoustic complexity indices reveal the acoustic communities of the old-growth Mediterranean forest of Sasso Fratino Integral Natural Reserve (Central Italy)

The Sasso Fratino Integral Natural Reserve (Central Italy), a rare example of climax Mediterranean forest, provides an extraordinary opportunity to create an important soundscape reference of old-growth forest. In this study, we describe the soundscape of three localities (Lama, Sasso 950, Sasso 1400) representative of a gradient of variety and complexity of habitats, recorded during the period 10 May to 9 June 2017. Our results reveal temporal partitioning into acoustically homogeneous periods across 24 h suggesting that soniferous species (mainly birds) adopt ecological routines in which their acoustic activity is organized according to specific transient physiological needs. We processed multi-temporal aggregates of 1, 5, 10, and 15 s recordings and calculated the Acoustic Signature (AS) with four new indices: Ecoacoustic Events (EE), Acoustic Signature Dissimilarity (ASD), and their fractal dimensions (DEE and DASD), derived from the Acoustic Complexity Index (ACI). The use of the EE and ASD greatly improved the AS interpretation, adding further details such as the emergence of a clear sequence of patterns consistent with the daily evolution of the overall soundscape. DEE and DASD confirm the patterns observed using the AS, but provide more clarity and detail about the great acoustic complexity that exists across temporal scales in this old-growth forest. The temporal turnover of different acoustic communities occurs as a result of a gradual shift of different homogenous acoustic properties. We conclude that soniferous species use distinct, species-specific temporal resolutions according to their physiological and ecological needs and that the fractal approach used here provides a novel tool to overcome the difficulties associated with describing multi-temporal acoustic patterns.

Customizing acoustic dirac cones and topological insulators in square lattices by topology optimization

Dirac point, the cornerstone of topological insulators, has been attracting ever-increasing attention due to its extraordinary properties. In this paper, a bottom-up topology optimization approach is established to systematically design the acoustic Dirac cones with customized double, triple and quadruple degeneracies at different wavelength scales. Using the proposed methodology, novel square-symmetric, chiral and orthogonal-symmetric sonic crystals (SCs) are constructed in a square lattice with tailored Dirac cones. The proposed design approach offers a unified framework to tailor SCs with exotic functionalities which are being widely researched in acoustic metamaterial community. As illustrative examples, zero-index acoustic cloaking and Talbot effect near the Dirac points of the optimized SCs are demonstrated numerically. Moreover, a novel acoustic pseudo-spin topological insulator is obtained, which entails a robust zigzag wave propagation and broadband, unidirectional, and topologically protected transport with a record-breaking relative bandwidth of 30.51%. The proposed design methodology shows promise and opens new horizons for customizing topological acoustics and conceiving high-efficiency wave devices.

Soundscape of urban-tolerant crickets (Orthoptera: Gryllidae, Trigonidiidae) in a tropical Southeast Asia city, Singapore

ABSTRACT Urbanisation impacts biodiversity tremendously, but a few species can still tolerate the harsh conditions of urban habitats. Studies regarding the impact of urbanisation on the soundscape and acoustic behaviours of sound-producing animals tend to overlook invertebrates, including the crickets. Almost nothing is known about their acoustic community in the urban environment, especially for Southeast Asia where rapid urbanisation is widespread. Grass verges in Singapore – characterised by complex mosaics of land-use types – were sampled as a microcosmic representation of the urban environment to address these questions: (i) What is the acoustic community of crickets in the urban environment? (ii) How do co-occurring species partition their calls? (iii) How do the call properties vary with environmental conditions and individuals? The calling songs of 10 species were recorded and they generally have distinct call signatures in both the time and frequency domains. The acoustic community was dominated by Polionemobius taprobanensis and Gryllodes sigillatus. They also showed repeatabilites in their call properties with static properties being more repeatable than dynamic properties, but these call properties were not associated with environmental variables. The presence of these crickets is relevant for a biophilic city as they represent what most urban dwelling humans could frequently hear.

A guild classification system proposed for anuran advertisement calls

Zoologists have widely acknowledged the utility of classification systems for characterising variation in anuran egg and clutch types, tadpole morphotypes, embryonic and tadpole development, amplexus types and reproductive modes. These classification systems have facilitated unambiguous communication between researchers, often working in completely different fields (e.g. taxonomy, ecology, behaviour), as well as comparisons among studies. A syntactic system, classifying anuran call guilds, is so far lacking. Based on examination of the calls of 1253 anuran species we present a simple, easy to use dichotomous key and guild system for classifying anuran advertisement calls – the call type most frequently emitted by anurans and studied by researchers. The use of only three call elements, namely clearly-defined calls, notes, and pulses, plus presence or absence of frequency modulation, allows assigning all currently known anuran advertisement calls to one of eight distinct call guilds defined here. This novel toolkit will facilitate comparative studies across the many thousand anuran species, and may help to unravel drivers of anuran call evolution, and to identify ecological patterns at the level of acoustic communities.