Ecoacoustics

The Ecological Role of Sounds

Almo Farina, Stuart H. Gage, Almo Farina, Stuart H. Gage

• Publisher: Wiley
• Year: 2017
• ISBN:
  9781119230717
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

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.

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).

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-Euro...