Ecoacoustics: The Ecological Role of Sounds

By Almo Farina

The sounds produced by geophonic, biophonic and technophonic sources are relevant to the function of natural and human modified ecosystems. Passive recording is one of the most non-invasive technologies as its use avoids human intrusion during acoustic surveys and facilitates the accumulation of huge amounts of acoustical data.

For the first time, this book collates and reviews the science behind ecoaucostics; illustrating the principles, methods and applications of this exciting new field. Topics covered in this comprehensive volume include;

• the assessment of biodiversity based on sounds emanating from a variety of environments
• the best technologies and methods necessary to investigate environmental sounds
• implications for climate change and urban systems
• the relationship between landscape ecology and ecoacoustics
• the conservation of soundscapes and the social value of ecoacoustics
• areas of potential future research.

An invaluable resource for scholars, researchers and students, Ecoacoustics: The Ecological Role of Sounds provides an unrivalled set of ideas, tools and references based on the current state of the field.

• Language: English
• Publisher: Wiley
• Release date: May 22, 2017
• ISBN: 9781119230717

Book preview

List of Contributors

Anne C. Axel

Department of Biological Sciences

Marshall University

Huntington

USA

Giuseppa Buscaino

BioAcousticsLab

National Research Council (IAMC-CNR) - Detached Unit of Capo Granitola (TP)

Italy

Maria Ceraulo

Department of Pure and Applied Sciences

University of Urbino

Urbino

Italy

Almo Farina

Department of Pure and Applied Sciences

University of Urbino

Urbino

Italy

Francesco Filiciotto

BioAcousticsLab

National Research Council (IAMC-CNR) - Detached Unit of Capo Granitola (TP)

Italy

Susan Fuller

Queensland University of Technology

Brisbane

Australia

Stuart H. Gage

Department of Entomology

Michigan State University

East Lansing

USA

Wooyeong Joo

Choongnam

Seocheon-gun

Maseo-Myeon

Geumgang-ro

South Korea

Eric P. Kasten

Michigan State University

East Lansing

USA

Bernie Krause

Wild Sanctuary

Glen Ellen

USA

David Monacchi

Conservatorio Gioachino Rossini

Pesaro

Italy

Timothy C. Mullet

Ecological Services

US Fish and Wildlife Service

Daphne

Alabama

USA

Brian Michael Napoletano

Centro de Investigaciones en Geografía Ambiental

Universidad Nacional Autónoma de México

Morelia

Michoacán

México

Susan E. Parks

107 College Place

Syracuse

USA

Gianni Pavan

CIBRA

University of Pavia

Italy

Nadia Pieretti

Department of Pure and Applied Sciences

University of Urbino

Urbino

Italy

Marisol A. Quintanilla-Tornel

Plant and Environmental Protection Sciences

University of Hawaii

Manoa

USA

Lyndsay Rankin

Northern Illinois University

DeKalb

USA

Denise Risch

Scottish Association for Marine Science (SAMS)

Oban

Scotland

UK

Michael Towsey

Queensland University of Technology

Brisbane

Australia

Preface

Discovering the importance of sound in natural processes is an important legacy of bioacoustics and human acoustics, two disciplines that have developed in the second half of the twentieth century. At that time, Aldo Leopold and Rachel Carson used acoustics to describe relevant phenomena like animal migration or the effect of chemical pollution on reproductive success of breeding birds but acoustics technology methods were rare. Their heritage is an important baseline for a new ecological perspective in the scientific investigation of sound, known as ecoacoustics, a discipline that incorporates and integrates the study of sound in both ecological and human systems.

Sound is an important phenomenon including behavioral functions that range from mate performance to territory defense and social cohesion and has recently been shown to be a key issue in ecological processes. The Earth emits geological, biological, and human sounds within the biosphere, creating a sonic context that characterizes ecosystems at different spatial and temporal scales and has consequences that can affect many ecological processes. Vocal animals have a direct relationship with habitat suitability and the vocal performance of other organisms, further confirming the energy investment required to produce acoustic signals and the trade-off between such performances, other life traits, and the availability of resources needed for their survivorship.

All young disciplines, including ecoacoustics, have difficulty in tracing historical origins so there is no precise date allocated to its foundation. The use of the term ecoacoustics was suggested at a meeting in June 2104 at the Museum of Natural History in Paris where soundscape ecology was also suggested as an alternative. The assembly decided that ecoacoustics was all-inclusive in studies of ecologically based sound and thus included soundscape ecology.

With this book, we offer examples of studies, theoretical concepts, and methodologies that have evolved over the past decades in an attempt to provide a synthesis of the new discipline of ecoacoustics, although we emphasize that these are only a subset of possible examples. This book is not a celebrative edition of a consolidated ecological discipline but a contribution to transmit the principles and ideas of ecoacoustics to a wider audience. We believe that the examples of these aspects of ecoacoustics will provide an incentive for others interested in ecological sounds, including those in the sciences and the arts, to pursue their research, applying sound to solve ecological problems and to educate the next generation about the importance of ecological sounds to the survivorship of the human race.

The 18 chapters in this book cover important topics to assist others to understand the ecological significance of sounds. This introduction to ecoacoustics is intended for all who are interested in or concerned about the ecosystems in which we live and utilize for the resources that they provide.

Almo Farina and Stuart H. Gage

Chapter 1

Ecoacoustics: A New Science

Almo Farina¹ and Stuart H. Gage²

¹Department of Pure and Applied Sciences, Urbino University, Urbino, Italy

²Department of Entomology, Michigan State University, East Lansing, USA

1.1 Ecoacoustics as a New Science

Ecoacoustics is the ecological investigation and interpretation of environmental sound (Sueur and Farina 2015). It is an emerging interdisciplinary science that investigates natural and anthropogenic sounds and their relationships with the environment over multiple scales of time and space. Ecoacoustics is inclusive of the realms of ecological investigation including populations, communities, ecosystems, landscapes, and biotic regions of the Earth system. Studies of ecoacoustics in these realms can include terrestrial, freshwater, and marine systems. Ecoacoustics thus extends the scope of acoustic investigations, including bioacoustics and soundscape ecology.

Ecoacoustics studies involve the investigation of sound as a subject to understand the properties of sound, its evolution, and its function in the environment. Ecoacoustics also considers sound as an ecological attribute that can be utilized to investigate a broad array of applications including the diversity, abundance, behavior, and dynamics of animals in the environment. To facilitate this emerging new science and the investigators interested in the study of ecoacoustics, the International Society of Ecoacoustics (ISE) has recently been established and details can be found at https://sites.google.com/site/ecoacousticssociety/. For definitions of other acoustics disciplines, see Pijanowski et al. (2011) and Farina (2014).

1.2 Characteristics of a Sound

Sound is a flow of energy in the form of lateral vibrations through a medium capable of oscillation. Sound is additive, meaning separate waves combine to form a single signal. The ear and brain manually separate this into distinct waves. The number of vibrations a sound produces per second is called frequency with a unit measurement of hertz. A spectrogram, commonly used to see a sound recording, is shown in Figure 1.1 where time is on the x-axis (seconds), frequency is on the y-axis (kilohertz), and sound intensity (energy) is on the z-axis. The spectrogram shown is a visual representation of a sound. The creation of a sound image requires that the sound be processed using fast Fourier transform (FFT). Creating a spectrogram using the FFT is a digital process. Digitally sampled data, in the time domain, is divided into components, which usually overlap, and Fourier transformed to calculate the magnitude of the frequency spectrum for each component. Each component then corresponds to a vertical line in the image – a measurement of magnitude versus frequency for a specific moment in time. The spectra or time plots are then laid side by side to form the image. The sound shown in Figure 1.1 was recorded in monaural at 22 050 Hz at site LA00 (45.53320, –84.291960 decimal degrees) on May 4 2009 at 0600h. Most of the sound in this recording occurs between frequencies 2 and 6 kHz with some high-frequency sounds occurring about 8 kHz and some low-frequency sounds at about 0.5 kHz. For those interested in the details of a mathematical treatment of acoustic signal processing, please see Hartmann (1998).

Illustration of A spectrogram from a recording made at site LA00.

Figure 1.1 A spectrogram from a recording made at site LA00 (45.53320, –84.291960 in decimal degrees) on May 4 2009 at 0600h.

1.3 Sound and its Importance

Hearing is one of the five key senses (hearing, vision, touch, smell, and taste) that allow organisms in the animal kingdom to relate with the environment. Hearing is an intrinsic component of the life of many organisms, including humans. Many animals use hearing to receive signals made by the environment or by other organisms. They derive meaning from these signals, which can range from danger to courtship, and these sound signals can often mean survival or a source of food. The importance of sound to humans has diminished due to evolution, since we have built habitation and created technology that we think protects us from the outside world. As our world has become louder, due to our increasing population and technological development, we are becoming more sensitive to the importance of sound. Sound is the heartbeat of the biosphere, the places on Earth where life exists. If we can measure this heartbeat, we can determine the condition of the biosphere. When one scales from biosphere, to eco-region, to landscape, to ecosystem or to habitat, the sounds produced within each of these realms can determine the condition of that realm if we can determine the type of sounds being emitted.

1.4 Ecoacoustics and Digital Sensors

Ecoacoustics has been recognized as an approach to the study of species communication and census species over long periods of time. There have been significant changes in monitoring technology. Ecoacoustics has been developed thanks to instrumentation and analytical techniques. For instance, the microphone is an important sensor because this single instrument can serve many purposes for ecological investigations when connected to a recorder. The array of ecological attributes that can be determined by a microphone, which is an analog for hearing, is broad compared to other types of available sensors (smell, taste, vision, touch). Sensors which measure other senses are important but are not yet fully applicable to the field as is the microphone, mainly due to cost.

Studies of animal attributes by listening to their sounds can be a fruitful undertaking, especially if one enjoys listening to and documenting the occurrence of animal species during the dawn or nighttime chorus. However, there are many pitfalls, including change in species composition over season and time of day and the potential for misidentification of species. Errors in species identification are introduced because an observer cannot be at multiple places at the same time. Within the past decade, analog tape recorders have been replaced by digital recorders. Clocks have been added to recorders so that recordings can be made at specific times and other environmental sensors have been incorporated in the same recording machine. The length of a recording period was previously limited due to high power consumption by processors. Just a few years ago, it was not possible to record in a remote place without being there to manage the recording unit. Today, sound recorders can be programmed to suit a project’s objective, can store many recordings on removable digital media and can remain active in the field for months without intervention. This change in technology has given rise to the use of sound as an ecological attribute. Modern acoustic sensors can be used to investigate several attributes of ecological significance. These may include practical and theoretical aspects of the environment, including acoustic identification of species in terrestrial and aquatic ecosystems; the vocal behaviors of specific organisms and their physiology; the study of noise pollution; and measuring ecological processes under a climate change scenario.

1.5 Ecoacoustics Attributes

A microphone and an automated recorder can provide an array of attributes that can have significant implications for theoretical and applied ecology. Important processes can be remotely investigated, including the number of species present, phenology of sound, trophic interactions, biological diversity, level of disturbance, diurnal and seasonal change of acoustic activity, level of habitat health, acoustic interactions between species, and complexity of the soundscape.

1.5.1 Population Census

Sound as a tool to survey animals has been utilized for decades (Ralph and Scott 1981). Birds are monitored by listening to the morning chorus and identifying the species based their signals at prescribed listening posts. Gage and Miller (1978) describe a long-term study using this method. Similar monitoring methods have utilized sound to determine species occurrence and abundance of amphibians using nighttime signaling (Karns 1986). The Breeding Bird Survey of North America (BBS) has been ongoing since the 1960s (Robbins and van Welzen 1967); it uses sound to determine avian species occurrence and this eco-region assessment has provided one of the longest records of bird species occurrence in North America, thus enabling the assessment of change in avian species. The surveys conducted by the BBS take place during the peak of the breeding season. The BBS routes are 24.5 miles long and there are 50 stops at every 0.5 mile along the route. Routes are randomly located in order to sample habitats that are representative of the entire region (Sauer et al. 1997). Although surveys are conducted differently in Europe, sound is used to determine the occurrence of bird species in many countries. The Pan-European Common Bird Monitoring Scheme commenced in January 2002; its main goal is to use common birds as indicators of the general state of nature using scientific data on changes in breeding bird populations across Europe (Voříšek et al. 2008).

1.5.2 Biological Diversity

Biological diversity is a complex ecological attribute to measure because it requires documentation of all species that inhabit a place. In addition, seasonal change can change biological diversity. Therefore, vegetation is commonly used as a surrogate for biological diversity. Measurement of the sound diversity at a site can begin to add information to the determination of biological diversity (Farina et al. 2005; Fuller et al. 2015; Sueur et al. 2008; Tucker et al. 2014).

1.5.3 Habitat Health

Habitat health is a relative term, but when defined by the types of sounds emitted from the site, these signals can provide an indication of the quality of that place. In fact, sounds differ in type and character depending on the types of vegetation and food available to the organisms. Benchmarks need to be established for urban, forest, grassland, and desert systems so that sounds in arrays of these systems can be compared (Fuller et al. 2015; Qi et al. 2008).

1.5.4 Time of Arrival/Departure of Migratory Species

The changing global climate is causing shifts in the arrival and departure times of animals that inhabit terrestrial and marine ecosystems (MacMynowski et al. 2007). Shifts in the areal pathways used by migratory animals to move from wintering sites to breeding sites may also be determined by measuring sounds along these marine or terrestrial routes.

1.5.5 Diurnal Change

Daily patterns of change in animal behavior can be determined by measuring sounds emitted from a place (Farina et al. 2015). Many factors can cause diurnal change and the measurement of sound along with weather information can help to describe the magnitude of the change (Gage and Axel 2013).

1.5.6 Seasonal Change

Seasonal change caused by climate shifts or physical disturbance of the Earth system due to large-scale natural events or by land use change due to human development can be measured by recording sounds in a place. Seasonal change is also a natural occurrence. In temperate regions, there are shifts in animal behavior as seasons change. In spring, migratory populations of marine and terrestrial animals (mammals, fish, birds) move from overwintering habitats to breeding locations that can be far distant and require a great expenditure of energy. Food and habitat resources change and during this period, the sounds emitted from these organisms differ as they enter the breeding cycle (Gage and Axel 2013).

1.5.7 Competition for Frequency

The acoustic niche hypothesis (Krause 1993), an early version of the term biophony (sounds made by organisms), describes the acoustic bandwidth partitioning process that occurs in still wild biomes by which nonhuman organisms adjust their vocalizations by frequency and time-shifting to compensate for acoustic habitat occupied by other vocal creatures. Thus each species evolves to establish and maintain its own acoustic bandwidth so that its voice is not masked (Malavasi and Farina 2013). For instance, examples of clear partitioning and species discrimination can be found in the spectrograms derived from the biophonic recordings made in most uncompromised tropical and subtropical rainforests (Krause 1993).

1.5.8 Trophic Interactions

Many species of organisms do not emit audible sounds but those that do emit acoustic signals may depend on organisms that do not. Therefore, the presence of those that do not emit sounds may be deduced by quantifying the sounds for those that produce auditory signals. Consider birds and their food source. A wood thrush sings a beautiful song in undisturbed forests and searches and feeds on worms and other food that occurs on the forest floor. Although the food sources do not make audible sounds, the wood thrush would not occur in the habitat if it were not for the resources found there. When we hear the sound of the thrush, we can infer that there are food resources nearby and thus identify trophic interactions.

1.5.9 Disturbance

Disturbance can be caused by natural events (hurricanes, volcanoes, fires, floods) or by human-caused events (mining, urbanization, forest harvest, spraying). Such events are characterized by acoustic emissions. The measurement of sounds (noise) caused by disturbance can indicate the type and duration of the disturbance. The term technophony, the sounds made by machines, is used to characterize disturbance and can occur when an overabundance of machine sounds from aircraft, automobiles, watercraft, chain saws, etc. dominates a habitat. Usually technophony occurs at lower sound frequencies than biota so it is possible to use sound to quantify disturbance.

1.5.10 Sounds of the Landscape and People

Every landscape has a specific acoustic signature that is the result of the mixture of all the physical and biological acoustic agents. The measurement of the sounds emitting from a place can provide an enjoyable experience to the listener. Listening to recordings of the howl of a coyote, the yodel of a common loon or the song of a thrush can conjure up memories of a place long forgotten. Figure 1.2 provides a summary of the value of sound ranging from population census to quality assessment of the landscape for human well-being.

List showing Ecoacoustics attributes.

Figure 1.2 Ecoacoustics has several competencies in environmental surveys, ranging from population census to quality assessment of landscape for human well-being.

1.6 Ecoacoustics and Ecosystem Management

There are two aspects of sound that relate to ecosystem management:

as a response indicator by estimating the diversity of vocal organisms; determining the relative proportions of human and natural activity; characterizing the daily and long-term trends of human and biological activity; and measuring sound in response to changes in land use.

as a stress indicator by examining the effects of human activity on organism communication during critical functions (e.g. reproduction, food tracking, migration, etc.); determining the causes of natural population declines in organisms sensitive to human disturbance or to climate change (Krause and Farina 2016).

Sound can also be used as a management tool to regulate the amount of noise that is tolerable to humans (Farina 2014, pp. 263–296). Sound maps of urban areas, airports, manufacturing zones, and parks can be useful tools to guide the development of sound abatement regulations. Measurement of sound can be used to identify and characterize the amount of technology (trucks, cars, boats, ships, jet skis, snow machines) and the length and intensity of human-kept animals (dogs, roosters) which can be a local disturbance.

1.7 Quantification of a Sound

1.7.1 Species Identification

One can listen to the sounds in a recording and identify the entities recorded. Haselmayer and Quinn (2000) compared field observations using the point-count method of species identification by listening to recordings made at the time of the point-count and found that they are highly correlated. Joo (2009) conducted a breeding bird survey and also identified species in simultaneous recordings and found a high correlation as well. Kasten et al. (2012) provide a method to catalog species heard in a recording using a web-based tool. Automated species identification has been found to be complex due to the variability within species of songs and calls and the overlap in frequencies caused by sound emitters. Butler et al. (2007) used signatures extracted from spectrograms to search other spectrograms for that signature providing the probability of match to that signature. Match probabilities are closer to 1 for simple signatures (insects, amphibians) compared to more complex signatures (birds). However, new approaches to this problem have made major improvements in automation of species identification (Acevedo et al. 2009; Dong et al. 2015; Duan et al. 2013).

To quantify sounds recorded in the environment, the spectrogram representation can be used to create acoustics indices by dividing the spectrogram into frequency intervals and counting the pixels in each interval (Napoletano 2004). The spectrogram can also be used to select signatures of a species from the image and search a series of spectrograms for that signature (Butler et al. 2007). Since these studies were undertaken, there has been considerable improvement in the development of acoustics indices and species recognition algorithms.

1.7.2 Acoustic Indices

Acoustic indices are derived from environmental recordings that do not depend on the species that occur in the recordings but rather on the characteristics of the recording, including the diversity of the sounds in the recording, the complexity of the sounds, the degree of evenness of the sounds, or ratios of frequencies in the sounds.

Seewave, a package in R developed by Sueur et al. (2008), provides functions for analyzing, manipulating, displaying, editing, and synthesizing time waves. This package processes time analysis (oscillograms and envelopes), spectral content, resonance quality factor, entropy, cross-correlation and autocorrelation, zero crossing, frequency coherence, dominant frequency, analytic signal, 2D and 3D spectrograms. Seewave enables a user to compute acoustic indices including H (Sueur et al. 2008), the Acoustic Complexity Index (ACI) (Pieretti et al. 2011), and the Normalized Difference Soundscape Index (NDSI) (Kasten et al. 2012).

Soundecology, another R package focusing on acoustics, was developed by Villanueva-Rivera et al. (2011) and enables a user to compute values for acoustic indices where one can specify the acoustic index and its parameters. Acoustics indices in R-Soundecology include the ACI (Pieretti et al. 2011), the Acoustic Diversity Index (Villanueva-Rivera et al. 2011), the Acoustic Evenness Index (Villanueva-Rivera et al. 2011), the Bioacoustic Index (Boelman et al. 2007) and the NDSI (Kasten et al. 2012). These indices and other techniques used to interpret environmental recordings are discussed in Chapter 16. A procedure to detect and identify acoustic events, the Ecoacoustic Event Detection and Identification (EEDI) developed by Farina et al. (2016). is powered by free access software, the SoundscapeMeter 2.0 (Farina and Salutari 2016).

1.8 Archiving Ecoacoustics Recordings

The new types of automated recorders can be programmed to record sounds based on project objectives. Recording may be continuous or recorders may be programmed to sample the environment by having the recorder wake up, record for a length of time, then sleep until the internal clock tells the recorder to wake and record again. There are many recording options that were not possible just a few years ago. For instance, recorders can be set to record continuously for one hour before sunrise to one hour after sunrise. One can purchase such recorders from companies like Wildlife Acoustics (www.wildlifeacoustics.com), Lunilettronik (www.lunilettronik.it/) or Frontiers Lab (www.frontierlabs.com.au/) or one can construct automated recorders (Aide et al. 2013; Farina et al. 2014; Gage et al. 2015; Mason et al. 2008; Wimmer et al. 2013). These types of recorders can amass many recordings. For example, a project which has been in operation since 2009 has made over 500 000 recordings to date from 12 sites at 30-minute intervals, each one minute in length (www.real.msu.edu/projects/one_proj.php?proj=la). The start and end recording dates are different depending on the intent. This requires an infrastructure to enable computation of sound metrics, storage of the sounds and their associated metrics and then retrieval of the sounds and/or the metrics for analysis. The Remote Environmental Assessment Laboratory’s Digital Acoustic Library System has these features and is described in Kasten et al. (2012), while Villanueva-Rivera and Pijanowski (2012) described Pumilio, a web-based system to archive acoustic recordings.

One may ask Why keep all these recordings? The answer is simple: When the project began in 2009, automated species recognition was a dream. Now it is becoming a reality. We can then use these historical recordings to automatically identify the species in the database (Aide et al. 2013; Dong et al. 2015). To complement the issues involved in automated species identification, methods have been developed to search for specific frequency intervals within the digital database since vocal organisms often signal within a range of frequencies (Kasten et al. 2012).

1.9 Ecological Forecasting

We depend on the Earth’s natural resources to sustain our economies and our life support. However, we are exploiting these resources at an unprecedented rate and thus undermining our economies and life support systems. This is a critical time in human history and we have the responsibility to measure and assess the effects of biological, chemical, physical, and human-induced change on the Earth system and its function. Ecological forecasts predict the effects of biological, chemical, physical, and human-induced changes on ecosystems. The ecological science community is entering a new era in which forecasts of ecological change can become commonplace if we bring to bear new tools, monitoring and observing systems, and increased understanding available today and on the horizon. We are poised to capitalize on new opportunities as we significantly change the way we anticipate and manage ecological risk. Sound is one of the key ecological attributes that can be used to monitor the heartbeat of the biosphere and thus enable ecological forecasting. The advent of automated sensors is revolutionizing environmental monitoring and leading to new thrusts in environmental research and education, including ecological forecasting (NSF 2015).

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Chapter 2

The Duality of Sounds: Ambient and Communication

Almo Farina¹ and Stuart H. Gage²

¹Department of Pure and Applied Sciences, Urbino University,, Urbino, Italy

²Department of Entomology, Michigan State University, East Lansing, USA

2.1 Introduction

In this chapter we address the ontology of sounds, their nature and function. Sounds are often considered as a means to communicate, but in this chapter sound is considered as a component of the environment and a passive source of information for animals and humans. Every organism requires precise information from the external world to make the right choice at the right time and finally to intercept the necessary resources to maintain itself and to accomplish vital functions (Farina 2012). The perception of the environment is committed to a species-specific censorship and to a successive cognitive and cultural elaboration of the signals that are coming from the external world (Farina et al. 2005).

If visual information is dominant in diurnal species, olfactory, tactile, and magnetic information prevails in nocturnal animals, whereas the chemical information is common between many organisms, from plants to humans, regardless of the presence or absence of light. This information is mediated by olfactory and tasting sensors. Acoustic information is a further important source of knowledge utilized by diurnal and nocturnal organisms in terrestrial and aquatic systems in order to communicate and detect the surrounding environment. Acoustic information is very common in nature, and its origin may be geophonic, biofonic or technophonic.

Acoustic information to which animals are sensitive has been explored for a long time with bioacoustics and behavioral approaches that describe the anatomy of sounds by partitioning song and call sequences into elementary components. The role of ambient sound is a subject that is rarely considered in ecological research and remains more popular in human acoustics (Davies et al. 2013). In reality, every organism is embedded in a sonic environment, the characteristics of which represent reference points to enable the accomplishment of important functions.

Animals living in groups, such as titmice, use extensively heterospecific signals that inform individuals about the presence of a threat (predators, humans) (Langham et al. 2006) and avoid areas dominated by strong or permanent noise that could mask their acoustic signals (Francis et al. 2009). Acoustic communities, such as temporary aggregations of singing species, are created according to an interspecific self-organized communication design (Farina and James 2016). Acoustic communities are sonic broadcasting centers that create a temporary sonic environment that in part copes with environmental conditions such as aspect, humidity, wind, and human sounds and that is strongly affected by the presence of active species. Acoustic communities are distributed across a landscape in a variable geometry due to the uneven distribution of resources and of interacting individuals.

2.2 Vegetation and Ecoacoustics

There are three major components that enable a sound-producing species to survive: a place to live, a place to reproduce, and food resources. Different species of vegetation provide these opportunities but differ in different ecosystems. For example, there are more vocal species in the tropics because there are more species of vegetation than in temperate systems. In temperate systems, there are more species in ecosystems that have a diversity of vegetation. The same is true for desert systems. The more species of vegetation, the more vocal species there are. Many vocal organisms in northern ecosystems migrate to southern areas where there are more abundant resources for survival. Because vocal animals require food for survival, more species occur in ecosystems which produce a diversity of food.

The Earth system is losing both complex and simple ecosystems which contain vegetation upon which vocal species rely for existence. These losses are due to deforestation and habitat fragmentation caused by expansion of croplands and pastures. Biodiversity loss caused by humans is identified as a major and challenging problem globally (Pimm et al. 2006), and threats to species and ecosystems will continue (Pereira et al. 2010). Examples include areas in South America, where significant changes in cropland expansion occurred between 1960 and1990 (Ramankkutty et al. 2002). Most of the cropland expansion occurred in the Brazilian Cerrado (woodland savannah), a region that has recently lost more than 9 million km (Brasil 2009; Klink and Machado 2005). In Borneo, remote sensing shows that the forest area has declined by 30.2% since 1973 (Gaveau et al. 2014). Therefore, specific long-term datasets are required to assess the dynamics of biodiversity in the region, which at present remain largely unknown (Molleman et al. 2006). Canada, Russia, and Brazil contain 65% of all the world’s intact forest landscapes (IFL) but these forests are becoming increasingly disturbed. In Canada, four provinces, Quebec, Alberta, Ontario, and British Columbia, account for 71% of the 216 199 km² of human disturbances (Global Forest Watch Canada 2016). The fragmented forest remnants of south-east Queensland, Australia, are noted for high biodiversity value and increased pressure associated with habitat fragmentation and urbanization (Tucker et al. 2014).

How biodiversity responds to habitat loss and fragmentation is one of the key topics in ecology and conservation biology (Sala et al. 2000). There is little understanding about the response of species and communities to human-induced stress (Gardner et al. 2009). Considering the rapid deforestation rate observed, it is important to develop and apply methods that can be effective for biodiversity assessment. Ecoacoustics techniques have been used in behavioral studies, and now these are also being applied to problems in conservation biology (Farina 2014; Ritts et al. 2016; Sueur et al. 2008; Towsey et al. 2014).

2.2.1 Vegetation Quality and Ecoacoustics

Tucker et al. (2014) studied 10 sites defined by a distinct open eucalypt forest community dominated by spotted gum (Corymbia citriodora ssp. variegata), which were stratified based on patch size and patch connectivity. Each site underwent a series of detailed vegetation condition and landscape assessments, together with bird surveys and acoustic analysis using relative soundscape power. Univariate and multivariate analyses indicated that the measurement of relative soundscape power reflects ecological condition and bird species richness, and is dependent on the extent of landscape fragmentation. The authors concluded that acoustic monitoring technologies provide a cost-effective tool for measuring ecological conditions, especially in conjunction with established field observations and recordings.

Fuller et al. (2015) examined how soundscape patterns vary with landscape configuration and condition. The goal of the 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 19 forest sites in eastern Australia. The study revealed that two indices, the Acoustic Complexity Index (Pieretti et al. 2011) and the Bioacoustics Index (Boelman et al. 2007), presented a similar pattern that was linked to avian song intensity, but was not related to landscape and biodiversity attributes. Two soundscape diversity indices, acoustic entropy (Sueur et al. 2008) and acoustic diversity (Villanueva-Rivera and Pijanowski 2011), and the Normalized Difference Soundscape Index (NDSI) (Gage and Axel 2013) revealed a high incidence of nighttime sounds, as well as a peak occurrence of sound energy at dawn and dusk chorus. The three indices that best connected the soundscape with landscape characteristics, ecological condition, and bird species richness were acoustic entropy (Sueur et al. 2008), acoustic evenness (Villaneuva-Rivera and Pijanowski 2011), and the Normalized Difference Soundscape Index (Gage and Axel 2013; Kasten 2012). The study showed that remote soundscape assessment can be implemented as an ecological monitoring tool in fragmented Australian forest landscapes.

2.2.2 Soundscape Indices and Biodiversity

Gasc et al. (2015) examined the limitations and bias in acoustic biodiversity indices. They revealed that none of the indices tested was able to